Static Routes and Default Routes

What is a Static Route

A static route is a route that is created manually by a network administrator. Static routes are typically used in smaller networks. In static routing, the Router’s routing table entries are populated manually by a network administrator.

The opposite of a static route is a dynamic route. In dynamic routing, the the routing table entries are populated with the help of routing protocols.

The major advantages of static routing are reduced routing protocol router overhead and reduced routing protocol network traffic. The major disadvantages of static routing are network changes require manual reconfiguration in routers and network outages cannot be automatically routed around. Also it is difficult to configure static routing in a complex network.

What is a Default Route

A Default Route (also known as the gateway of last resort) is a special type of static route. Where a static route specifies a path a router should use to reach a specific destination, a default route specifies a path the router should use if it doesn’t know how to reach the destination.

Default Route is the network route used by a router when there is no other known route exists for a given IP datagram’s destination address. All the IP datagrams with unknown destination address are sent to the default route.

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Administrative Distance

Administrative Distance (AD) is a value that routers use in order to select the best path when there are two or more different routes to the same destination from two different routing protocols. Administrative Distance counts the reliability of a routing protocol. Administrative Distance (AD) is a numeric value which can range from 0 to 255. A smaller Administrative Distance (AD) is more trusted by a router, therefore the best Administrative Distance (AD) being 0 and the worst, 255.

Administrative Distance (AD) Route Type
0 Connected interface
0 or 1 Static Route
90 Internal EIGRP Route (within the same Autonomous System (AS))
100 IGRP Route
110 OSPF Route
115 IS-IS
120 RIP Route
255 Unknown Route

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Protocol, Routing

Dynamic Routing Protocol


In the previous chapter, we looked at static routing. We saw how the router finds the best path to a network. We configured static routes and traffic was able to flow between two points.

In this chapter, we will give an overview of dynamic routing protocols. We will define them and learn how they are different from static routes. We will discuss their advantages over static routes, learn the different categories of dynamic routing protocols as well as classless and classful nature. We will also talk about the administrative distance and the metric.

Consider the network diagram shown below.

The administrative overhead that would be needed to make communication between all these devices would be considerable. All the static routes would have to be configured.

Wouldn’t it be much easier, for the network administrator to just “Teach” the routers how to get from one point to another? The solution to this problem would be dynamic routing protocols.

Dynamic routing protocols are a solution that is used in large networks so as to reduce the complexity in configuration that would be occasioned by having to configure static routes. In most networks you will see a mix of both dynamic and static routes.

Definition of dynamic routing protocols

Routing protocols are used to enable the routers exchange routing information, they allow routers to learn about remotely connected networks dynamically. This information is then added to their routing tables as a basis for forwarding packets.


Dynamic routing protocols can be classified in several ways.

  • Interior and exterior gateway routing protocols,
  • Distance vector, path vector and link state routing protocols,
  • Classful and classless.

The table below shows the various categories of dynamic routing protocols and the ones highlighted inred
will be the focus of this course. Others will be discussed at the CCNP and the CCIE level.

In this course, we will look at EIGRP, OSPFv2 and OSPFv3. These topics will be crucial in passing both your ICND1 and ICND 2 exam, and the CCNA composite exams.

The table below shows more information on the routing protocols to be covered in this course.

Acronym Full name standard year RFC
EIGRP Enhanced Interior Gateway Routing Protocol CISCO 1992 NULL
OSPFv2 Open Shortest Path First version 2 Open 1991 5709
OSPFv3 Open Shortest Path First version 3 Open 1999 5838

Although you may not be examined on the information above directly, both exams will have questions that require knowledge of this information.

Operation of routing protocols

Now that we have an overview of routing protocols, we need to understand how they work.

Routing protocols are comprised of processes, messages and algorithms that are used by routers to learn about remotely connected networks from routers that have been configured with the same routing protocols, the routes that have been learnt are added to the routing table and used as a basis for forwarding packets.

  • Routing protocols function by:
  • Discovering remote networks
  • Maintaining current routing information
  • Path determination

The routing protocol is made up of these components.

  1. Data structures – this is information about remote networks. It is usually stored in the RAM and may be comprised of tables such as neighbor tables and topology tables.
  2. Algorithm – this is the sequential list of steps that the routing takes when determining the best path to a particular network.
  3. Routing protocol messages – these are messages that are used to maintain updated routing information. Examples include; hello messages, update messages among others.

The way routing protocols operate may differ depending on the routing protocol, however, there are certain characteristics inherent in every routing protocol.

  • Exchange of information on interfaces to discover neighboring routers
  • Exchange of routes that have been advertised
  • Running of the algorithm so as to determine the best path
  • Adding of best paths to the routing table
  • Detection of topology changes and making the necessary changes

These are the general steps routers will take. However, the processes differ with each routing protocol and will be discussed at a later stage.

Advantages and disadvantages

Now that we have seen the dynamic routing protocols to be covered in this course, we need to know the advantages and disadvantages of using dynamic routing protocols. We also need to compare them to static routes.


  • Exchange of routing information when there is a topology change is dynamic.
  • Less administrative overhead as compared to static routes which have to be manually configured
  • Less error prone than static routing which.
  • Scalability, since there is less administrative overhead than static routes.


  • Require more expertise by the administrator, they are not as simple to configure as static routes.
  • They use more of the routers resources; such as CPU and RAM.

Egp vs igp

As mentioned earlier, routing protocols fall into two main categories which are;

  • EGP – Exterior Gateway Protocols
  • IGP – Interior Gateway Protocols

This categorization, is based on the Autonomous Systems.

Autonomous systems also known as routing domains; are collections of routers under the same administration. This may mean the routers that are owned by one company.

For example, company XYZ, could have 1 branch connected to the headquarters through a leased line. The networks owned and managed by XYZ would be one autonomous system, while the leased line and interconnections between the branch office and the headquarters which are controlled by the ISP would be another autonomous system. This is shown in the exhibit below.

The networks controlled by XYZ are labelled as AS 100 while AS 650 represents the ISP.

Interior Gateway Protocols (IGP) are used for intra-autonomous system routing – routing inside an autonomous system.

Exterior Gateway Protocols (EGP) are used for inter-autonomous system routing – routing between autonomous systems.

In this scenario for example, routing between XYZ headquarters and the branch office would use and IGP, whilst routing between company XYZ and the ISP would use an EGP.

Distance vector routing protocols vs. link state routing protocols

Interior Gateway Protocols (IGPs) can be classified as two types:

  • Distance vector routing protocols
  • Link-state routing protocols

Distance vector means that routes are advertised as vectors of distance and direction. If we take an example of a tourist getting directions, distance vector protocols would be where the tourist would only use road signs to get to where they are going. They do not know the exact landscape and possible blocks, they only know of the next point towards their destination.

Distance vector protocols work best in situations where:

  • The network is simple and flat and does not require a special hierarchical design.
  • The administrators do not have enough knowledge to configure and troubleshoot link-state protocols.
  • Specific types of networks, such as hub-and-spoke networks, are being implemented.
  • Worst-case convergence times in a network are not a concern

On the other hand, if the tourist had an entire map of the desired destination, with details of different paths to where they were going, they would be using a link-state routing protocol.

Link state routing protocols usually have a complete view of the topology. They usually know of the best paths as well as backup paths to networks. Link state protocols use the shortest-path first algorithm to find the best path to a network.

Link-state protocols work best in situations where:

  • The network design is hierarchical, usually occurring in large networks.
  • The administrators have a good knowledge of the implemented link-state routing protocol.
  • Fast convergence of the network is crucial.

Classful and classless

Classful Routing Protocols

Classful routing protocols don’t include the subnet mask in their routing updates. This is because they were designed prior to the introduction of CIDR and VLSM. RIPv1 is an example of such protocols.

Since they do not include the subnet mask in their routing updates, they cannot work where the networks have been subnetted.

Classless routing protocols

Classless routing protocols include the subnet mask with the network address in routing updates.

In this course, we will focus on the classless routing protocols since the use of classful routing protocols is outdated and no longer used in most modern networks.

Administrative distance and metric


Suppose a router has more than 1 destination to a network, how would it determine the best path to that network?

The metric, is the mechanism used by the routing protocol to assign costs to reach remote networks. In the tourist example, this may be the amount of fuel the tourist has to use to get to their destination. The metric is used to determine the best path to a network when there are multiple paths.

The table below shows the various metrics used by routing protocols which will be covered in this course.

Routing protocol Metric Description
RIPv1 Hop count The number of routers between the source and destination network.
RIPv2 Hop count The number of routers between the source and destination network.
EIGRP Composite metric A combination of several values used to determine the best path. The composite metric will be discussed in the chapter on EIGRP.
OSPFv2 Cost The bandwith or cost configured from the router to the destination network
OSPFv3 Cost The bandwith or cost configured from the router to the destination network

Understanding the different costs types will be crucial in your final exam.

Administrative distance

What if we had configured several routing protocols on one router, how would the router determine the best path to the desired network?

The administrative distance is the way routers use to give preference to routing sources. For example if a router learns of the same route via EIGRP and RIP, it will prefer the route it learnt via EIGRP.

All routes in the routing table are prioritized. With the best and most preferred paths being the directly connected routes. The AD is the trustworthiness of a route.

The AD is usually a value from 0 to 255, the lower the value the better the routing source, a route with an administrative distance of 255 will never be trusted.

If we use the tourist example, the administrative distance would be the trust placed on each means of transport, for example an airline would be more trusted over walking.

The table below shows the various administrative distances for the routing protocols which will be covered in this course.

Routing protocol Administrative distance
RIP 120
OSPF 110
Static routes 1


In this chapter, we have learnt about dynamic routing protocols. We defined and classified the various routing protocols. We explained how they work as well as their advantages and disadvantages. We also looked at the various classifications of routing protocols such as; EGP and IGP and distance vector and link state routing protocols. We also looked at classful and classless routing protocols as well as explained what the metric and administrative distance mean.

NOTE: The concepts learnt in this chapter are crucial in understanding routing. These concepts are usually examined in both ICND 1 and ICND 2 as well as the CCNA composite exam. These concepts will also be useful at the CCNP and CCIE levels.

In the next chapter, we will look at the first routing of this course which is EIGRP.

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Protocol, Routing

Static Routing Protocol


Welcome to the world of routing. In the next few chapters, we will look at how packets find their way in networks through routers. In this chapter, we will learn static routing.

Routers in our networks discover remote networks in one of two ways;

  1. Statically configured routes
  2. Dynamic routing protocols

We will learn various concepts on static routes such as how to configure static routes, how the routing table bases its decisions, routing interfaces among other concepts.


as you may already know, the work of the router is to forward packets from the source device to the destination device. In between there may be several routers. The router uses a database known as the routing table to forward these packets.

In previous chapters, we connected a router to computer and verified communication by using ping. However, refer to the topology shown in the exhibit below.


The network above shows a small network consisting of 3 routers and 2 hosts. As discussed earlier, each connection to a router should have its own network segment and this is shown in the diagram.

The network administrator also configured R1’s and R3’s serial interfaces as the DCE and all other configurations are correct.

In this scenario, R1 can ping HOST A, R1 can ping R2 s0/0/0 interface but not interface s0/0/1.

R3 can ping HOST B, R3 can ping R2’s s0/0/1 interface ONLY. HOST A and HOST B cannot communicate. As shown in the exhibit below.

In this chapter, we will explain the reasons as to why these two computers cannot communicate and resolve this problem.


Directly connected networks

The routing table is the database that contains information about various networks, we have said that these remote networks may either be learnt through routing protocols or manually configured routes.

The output of the “show ip route” command on a router, shows the routes that a particular router can reach. By default, a router will only know of directly connected routes.

Directly connected routes in our scenario, from R1’s perspective are the network connected to HOST A and the network between R1 and R2.

Since no other configuration has been made on these routers, R2 and R3, should only have directly connected routes.

The directly connected networks are the only networks that can be reached by a particular router. In our scenario, this means that;

  • Host A can ping R1
  • R1 can ping R2’s s0/0/0 interface but not interface s0/0/1
  • R2 can ping R1’s s0/0/0 interface but not interface fa0/0 or HOST A
  • R2 can ping R3’s s0/0/0 interface but not interface fa0/0 or HOST B
  • R3 can ping R2’s s0/0/1 interface but not interface s0/0/0
  • HOST B can ping R3.
  • Neither hosts can ping each other
  • R1 and R3 cannot ping each other.

The figure shown below shows all the directly connected networks.

Static routing

Static routes are one way we can communicate to remote networks. In production networks, static routes are mainly configured when routing from a particular network to a stub network.

stub networks are networks that can only be accessed through one point or one interface.

In the above scenario, the and networks are stub networks. This means that for hosts in these network segments only have one way to communicate with other hosts, which is R1 and R3 for the and networks respectively.

Understanding stub networks is crucial in understanding static routing.

The command needed to configure a static route is shown below.

Router(config)# ip route (network-address) (subnet-mask) (next-hop ip address/ exit interface)

The table below explains the meaning of each of the parameters in the ip route command as well as an example of the command which would be used on R1 to configure a static route to R3’s LAN network (

Parameter Meaning example
Ip route State that the route being configured is a static route Ip route
Network-address The network address of the destination network. This is the network I am trying to reach.
Subnet-mask The network address of the destination network that I am trying to reach
Next hop ip address This is the ip address of the router that is connecting me to the desired network
Exit interface This is the exit point interface on my router that connects to the router that will take me to the desired network s0/0/0


Refer to the exhibit. Therefore to configure a static route on R1 for network, the command to be issued on R1 is:

R1(config)# ip route

R1(config)# ip route


R1(config)# ip route s0/0/0

R1(config)# ip route s0/0/0

NOTE: When configuring static routes
you should only use either the exit interface or the next hop ip address and not both. This will be explained later.



Highlighted in
at the bottom of the show ip route output on R1, is the static route that we just added. The “S” at the beginning means that the routing table got this route as a result of a static route configuration.

In the braces, “1”, is the administrative distance for static routes, and “0” is the metric.

From this we can assume that pings from HOST A to HOST B should work. Right?

Let’s try a ping from HOST A TO HOST B and see what happens.


As you can see from the exhibit above, all four pings to HOST B are shown as request timed out. Further, highlighted in red
at the bottom, no packets were received by HOST B. this means that they could not communicate.

In the next section, we will explore why the two hosts could not communicate yet R1 was correctly configured with a static route.

Routing table principles

There are three routing table principles that dictate how routers communicate.

Principle 1:

routers forward packets based on information contained in their routing tables ONLY.”

R1 has 2 routes which is the connection between R2 and R3, and, which is the network on which HOST B is located. Therefore, based on the first principle, R1 will make its forwarding decisions based on this information only. It will not consult R2 or R3.Nor does it know whether or not those routers have routes to other networks. As a network administrator, it is your responsibility to make sure that all the routers in a network know about remote networks.

Principle 2:

” Routing information on one router does not mean that other routers in the domain have the same information.”

R1 doesn’t know about the information in R2’s routing table. The same can be said of R2 and R3. Therefore, the fact that R1 has a path to the networks connected to R2 and R3 does not mean that R2 and R3 have the same information.

For example, can reach the network on R3 through R2. R1 does not know whether R2 can reach the network connected to R3. Therefore, we need to configure routes from R2 to the LAN connected to R3.

Using Principle 2, we still need to configure the proper routing on the other routers (R2 and R3) to make sure that they have routes to these three networks.

Principle 3:

“Routes on a router to a remote network do not mean that the remote router has return paths.”

This principle means that when a route is configured on one router, the remote router must be configured with a return route. In our networks, most of the communication is bidirectional, this means that for every message we send, a reply is expected.

If we use the analogy of the post office, it would be like sending a letter without a return address. The recipient cannot reply to a letter without a return address, and the postman would not know where to send the letter.

In our scenario, this means that, when we configure a route to network on R1, we need to configure a route on the remote routers that leads to the LANs connected to R1.

Using Principle 3 as guidance, we will configure proper static routes on the other routers to make sure they have routes back to the network.

Applying the principles:

In this scenario, we need to apply all the three principles on all the routers so that the static routes can work.

Principle 1

R1 knows how to get to network, and network, however, R2 and R3 do not know how to get there. Therefore, we need to configure a static route on R2 so that it can know how to get to

Principle 2

We configured a static route on R1, however, this does not mean that R2 knows a path to network. Therefore this router needs to know about that network.

Principle 3

Even though R1 and R2 have a route to network, a ping would still fail because both R2 and R3 would not know how to get to R1. Therefore, we need to configure a route that gets back to network on this case we are using the next-hop ip address on both R2 and R3.

From this. We can now make the necessary configurations on all the routers to make communication between HOST A and HOST B possible.

On router R2:

R2(config)# ip route

R2(config)# ip route

On router R3:

R3(config)# ip route

R3(config)# ip route

When all the configurations have been made on all the three routers, communication between HOST A and HOST B should be possible. The figure below shows the routing tables of all the three routers, the static routes have been highlighted in red.







As a result of this output. We should be able to ping from HOST A to HOST B. the output below shows the results of the ping from HOST A to HOST B.


The output shows that there are replies coming from HOST B which has the ip address, the highlighted section in red shows that 4 packets were sent and all 4 were received by HOST B, with 0% loss.

Therefore, we have successfully configured static routing on the routers.

Resolving the next- hop ip address

Suppose we configured R2 with the next-hop ip address not an exit interface, how would the router know which interface to send the packets through?

Refer to the output of the show ip route command on R2, below.


When the router wants to send a packet to the network, it will look at the routing table.

There is a route to that network via Then the router checks to see whether it has an interface that to the network. In this scenario, that would be the network highlighted in blue. The exit interface is serial 0/0/0.

Routes that only have the next-hop ip address and no exit interfaces, must have resolve the next hop ip address using a route on their routing table that connects to the remote network.

In most cases, the route that the next hop is resolved to is usually a directly connected network.

As such, this is usually an issue, since the router has to process a packet twice before it can determine where to forward it. This is known as a recursive lookup.

It is recommended that static routes have an exit interface as opposed to the next hop ip address.

Summary and default routes

Suppose a router has more than 1 LAN connected to it. It would be more practical to use an address that covers all the LANS, and configure 1 static route. Take this scenario, R1 has 5 LANs connected to it;


Summarizing these routes is shown in the table below.


The first 2 octets and the first 5 bits from the left, in the third octet.

Therefore the new summary network address and subnet mask for the 5 networks will be: with the subnet mask as

When configuring a static route to the summary network out serial0/0/0 on R2, the command would be;

R2(config)# ip route s0/0/0

Refer to the exhibit shown below. Suppose HOST A wants to send an email to a friend or wants to view a website on the internet, how would the router know where to send the packets?

The internet has many ip addresses, and configuring one static route to a specific network would not work. Therefore, a default route is needed.

A default static route is a route that will match all packets. Default static routes are used:

When no other routes in the routing table match the packet’s destination IP address. In other words, when a more specific match does not exist. A common use is when connecting a company’s edge router to the ISP network.

When a router has only one other router to which it is connected. This condition is known as a stub router.

The syntax for configuring a static default route is:

Router(config)# ip route [next-hop ip address/ exit interface]

A route to this network would tell the router to forward any packet for which it does not have a route to the indicated next-hop ip address or exit interface.

In this scenario, to configure a default static route, the command sequence on R1 would be.

R1(config)# ip route


R1(config)# ip route s0/0/0


In this chapter, we have learnt how a router finds a path to a remote network, we have configured static routes using the principles of the routing table, learnt about the recursive lookup, as well as configured summary routes and default static routes.

In the next chapter, we will get into the world of dynamic routing protocols.

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Difference between Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (EGP)

Interior Gateway Protocol (IGP) is a Routing Protocol which is used to find network path information within anAutonomous System.

Known Interior Gateway Protocol (IGP) Routing Protocols are Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS)

Exterior Gateway Protocol (EGP) is a Routing Protocol which is used to find network path information between different Autonomous Systems. Exterior Gateway Protocol (EGP) is commonly used in the Internet to exchange routing table information. There is only one Exterior Gateway Protocol (EGP) exists now and it is Border Gateway Protocol (BGP).

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Autonomous System | Autonomous System Number

                        An Autonomous System (AS) is a group of networks under a single administrative control which could be an Internet Service Provider (ISP) or a large Enterprise Organization. An Interior Gateway Protocol (IGP) refers to a routing protocol that handles routing within a single autonomous system. IGPs include RIP, IGRP, EIGRP, and OSPF. An Exterior Gateway Protocol (EGP) handles routing between different Autonomous Systems (AS). Border Gateway Protocol (BGP) is an EGP. BGP is used to route traffic across the Internet backbone between different Autonomous Systems.

When BGP (Border Gateway Protocol) was at development and standardization stage, a 16-bit binary number was used as the Autonomous System Number (ASN) to identify the Autonomous Systems. 16-bit Autonomous System Number (ASN) is also known as 2-Octet Autonomous System Number (ASN). By using a 16 bit binary number, we can represent (2 16) numbers, which is equal to 65536 in decimals.

The Autonomous System Number (ASN) value 0 is reserved, and the largest ASN value 65,535, is also reserved. The values, from 1 to 64,511, are available for use in Internet routing, and the values 64,512 to 65,534 is designated for private use.

Available 16-bit (2-Octet) Autonomous System Numbers (ASN) were in verge of depletion by middle of 2011. To provide more Autonomous System Numbers (ASN), IETF published RFC 4893 in May 2007, which introduced 32-bit AS numbers. 32-bit Autonomous System Number (ASN) is also known as 4-Octet Autonomous System Number (ASN). 32-bit (4-Octet) AS numbers are represented as either as simple integers, or in the form x.y, where x and y are 16-bit numbers. Numbers of the form 0.y are exactly the previous 16-bit AS numbers.

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Difference Between Routable Protocol and Non-Routable Protocol

Routable protocol

A Routable protocol is a network protocol which can carry data from one network and can pass through the router to reach another network and be delivered to a computer in that remote network.

Examples of routable protocols: Internet Protocol (IP -IPv4 and IPv6), IPX, AppleTalk, VINES Internetwork Protocol (VIP), DECnet

Routable Protocol

Non-routable protocols

A non-routable protocol’s data cannot be passed through a router to reach a remote network. This is mainly because of the lack of capability of protocol (almost all non-routable protocols are designed long back which will not fit well in current networks) and the addressing scheme the non-routable protocol is using.

Non-routing protocols reachability limit is its own network and they are designed in such a way to think that all computers they communicate are on the same network as the source computer.

Non Routable Protocol

Examples of non-routable protocols: Local Area Transport Protocol (LAT), NetBios Extended User Interface (NetBEUI).

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Router Interface Naming Convention

Cisco Routers different types of interfaces like Serial, Ethernet, Fast Ethernet, Gigabit Ethernet, Tokenring,  FDDI are some of them (A single router may not have all these). The speed of Ethernet, Fast Ethernet and Gigabit Ethernet are different. The speed of Ethernet is 10 Mbps (Megabits per second), Fast Ethernet is 100 Mbps (Megabits per second) and Gigabit Ethernet is 1 Gbps (Gigabits per second)

Most of the latest routers are modular routers. Modular routers are expandable routers by using plug-in components.

The following naming convention is followed for a Cisco Router.


Slot numbers begin with 0 and port numbers begin with 0. Hence the name of the first interface of a WIC2T (modular card with two smart serial interfaces) is serial0/0 and the name of the second port is serial0/1. The short form of the two interface is s0/0 and s0/1.

Old 2500 series routers are not modular, and they had fixed ports. The interface naming convention of these routers is

<Interface_Type>< Port_Number>

Hence the name of the first Ethernet interface for non-modular router is ethernet0 or e0, and first Serial interface is serial0 or s0.


Important Key Combinations of Cisco IOS Command Line Interface (CLI), Cisco IOS Shortcut Keys

Following keys combinations are very useful while working with Cisco IOS Command Line Interface (CLI). Most important Cisco IOS Shortcut Keys are

Key Combination



Cursor moves to the “Beginning” of the Line.


Cursor moves to the “End” of the line


Cursor moves back “Back One Character”. (or Left Arrow)


Cursor moves forward “Back One Character”. (or Right Arrow)


Cursor moves “Backward to the Beginning of the Next Word”.


 Cursor moves “Forward to the Beginning of the Next Word”.


Erases the line completely


Erases the word the cursor is under


Move  from Configuration mode back to Privilege EXEC mode



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Basic Cisco Router Configuration Commands

How to Configure a Router Hostname

To configure a name for router, use hostname command from Global Configuration mode.

Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#hostname router1

How to Configure a MOTD Banner for Router

Users will be presented with a MOTD (Message of the DAY) banner every time they attempt a connection via the console port, auxiliary port, or a telnet session to router. Use the following commands to configure a MOTD message. Here the “#” character is known as a delimiting character. The banner message should be sorrounded by delimiting character and the message should not contain the delimiting character.

router1#configure terminal
router1(config)#banner motd #Welcome to

How to enable DNS lookup

To configure a DNS server for your router, follow these steps.

router1#configure terminal
router1(config)#ip name-server

How to turn off the automatic name resolution

The router is set by default to try to resolve any word that is not a command to a DNS server at address limited broadcast IP Address We can turn off this by using the following command.

router1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
router1(config)#no ip domain-lookup

How to assign a Local Name to an IP address

Following command assigns a host name to an IP address. Once this is completed, we can use the configured host name for telnet or ping.


router1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
router1(config)#ip host PC001

How to Turn on synchronous logging

If the router sends a message to the console while you’re entering a command, by default the router will interrupt your work to show the message.

If you want the information sent to console not interrupt the command you are typing, turn on synchronous logging.

router1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
router1(config)#line console 0
router1(config-line)#logging synchronous

How to configure an inactivity time-out for automatic log-off

Sets time limit when console automatically logs off. Set to 0 0 (minutes seconds) means console never logs off.


router1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
router1(config)#line console 0
router1(config-line)#exec-timeout 3 0

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Configure Passwords to Secure Cisco Router

How to password protect Console Port

To configure the console password, follow these steps.

Router(config)# line console 0
Router(config-line)# password CISCO
Router(config-line)# login

How to password protect Auxilary (AUX Port) Port

To configure the auxilary password, follow these steps.

Router#config t
Router(config)#line aux 0
Router(config-line)#password cisco
Router(config-line)# Ctrl-Z

How to password protect VTY Ports (Telnet Ports)

Configuring the VTY password is very similar to doing the Console and Aux ones. The only difference is that there are 5 VTY virtual ports, which are named 0, 1, 2, 3, and 4. You can use the shortcut 0 4 (a zero, a space, and 4) to set all 5 passwords at the same time. To configure the VTY password, follow these steps.

Router#config t
Router(config)#line vty 0 4
Router(config-line)#password cisco
Router(config-line)# Ctrl-Z

How to password protect Privileged Mode

The Enable Password is the old form of the password for “Privileged Mode”. Here the password is stored un-encrypted.

Router#config t
Router(config)#enable password cisco
Router(config-line)# Ctrl-Z

Enable Secret provides better security since password is kept encrypted using irreversible encryption algorithm.

Router#config t
Router(config)#enable secret cisco
Router(config-line)# Ctrl-Z

 Posted By – RamCruiseWalker


Cisco IOS Command Lines Modes

Cisco IOS Command Lines Modes, What is User mode, Privileged mode and Global Configuration mode

         Cisco IOS has a Command Line Interface (CLI) and it has three command line modes. Each mode has access to different set of IOS commands.

User mode (User EXEC mode)

User Mode is the first mode a user has access to after logging into the router. The user mode can be identified by the > prompt following the router name. This mode allows the user to execute only the basic commands, such as those that show the system’s status. The router cannot be configured or restarted from this mode.

The user mode can be identified as shown below


Privileged mode (Privileged EXEC Mode)

Privileged mode mode allows users to view the system configuration, restart the system, and enter router configuration mode. Privileged mode also allows all the commands that are available in user mode. Privileged mode can be identified by the # prompt following the router name. From the user mode, a user can change to Privileged mode, by running the “enable” command. Also we can keep a enable password or enable secret to restrict access to Privileged mode. An enable secret password uses stronger encryption when it is stored in the configuration file and it is more safe.

The Privileged mode can be identified as shown below


Global Configuration mode

Global Configuration mode mode allows users to modify the running system configuration. From the Privileged mode a user can move to configuration mode by running the “configure terminal” command from privileged mode. To exit configuration mode, the user can enter “end” command or press Ctrl-Z key combination.

The Global Configuration mode can be identified as shown below.


Global Configuration mode has various submodes, starting with global configuration mode, which can be identified by the (config)# prompt following the router name. Following are the important Global Configuration submodes.

Interface mode (Router physical interface configuration mode)


Subinterface mode (Router sub-interface configuration mode)


Line mode (Router line configuration mode – console, vty etc.)


Router configuration mode (Routing protocols configuration mode.)



Posted By – RamCruiseWalker


Upgrade or install IOS from Trivial File Transfer Protocol (TFTP) Server

To install IOS from TFTP server, follow these steps.

1) If you want a fresh install, erase the contents of the flash memory using the “erase” command as shown below.

Router01#erase flash
Erasing the flash filesystem will remove all files! Continue? [confirm]y
Erasing device... eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
<outout omitted>
eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee ...erasedee
Erase of flash: complete

2) Copy an IOS file from TFTP server to flash memory. Make sure that you have the IOS file available in the root of the TFTP server.

To copy an IOS file from TFTP server to the flash memory, use the following command from privilege mode.

Router01#copy tftp flash
Address or name of remote host []?
Source filename [C2600-Adventerprisek9-Mz_124-2_T.bin]?
Destination filename [C2600-Adventerprisek9-Mz_124-2_T.bin]?
Accessing tftp://
Erase flash: before copying? [confirm]y
Erasing the flash filesystem will remove all files! Continue? [confirm]y
Erasing device... eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
  <output omitted>
Erase of flash: complete
Loading C2600-Adventerprisek9-Mz_124-2_T.bin from (via FastEthernet0/0): !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  <output omitted>
[OK - 29771296 bytes]
Verifying checksum...  OK (0xECA5)
29771296 bytes copied in 376.332 secs (79109 bytes/sec)

After the IOS image file is copied to flash, you must reboot your router in order for it to use the new image. There are two ways you can reboot your router.

Power if off and then power it on (Hard reboot)

Run the “reload” IOS command from privilege mode (Soft reboot)


Backup IOS and configuration files to Trivial File Transfer Protocol (TFTP) Server

How to copy the contents of flash memory to TFTP Server

To copy the contents of the flash (IOS file is stored in flash memory) memory to TFTP server, use the following command from privileged mode.

Router01#copy flash tftp
Source filename []? C2600-Adventerprisek9-Mz_124-2_T.bin
Address or name of remote host []?
Destination filename [C2600-Adventerprisek9-Mz_124-2_T.bin]?
<output omitted>
29771296 bytes copied in 139.732 secs (213060 bytes/sec)

The file will be copied to the root folder of the TFTP server.

How to backup Running Configuration File to TFTP Server

To back up Running Configuration File to TFTP server, use the following command.

Router01# copy running-config tftp



Naming Convention of Cisco IOS Image Files

              IOS is the Operating System software used on Cisco routers and current Cisco Network Switches.Cisco IOS (Internetwork Operating System) image file is normally stored in flash memory and it has a naming convention.

Following output shows the “show-flash” command from privileged mode.

Ramanece #show flash
System flash directory:
  File  Length   Name/status
  3   5571584   c2600-i-mz.122-28.bin
  2   28282     sigdef-category.xml
  1   227537    sigdef-default.xml
                    [5827403 bytes used, 58188981 available, 64016384 total]
                    63488K bytes of processor board System flash (Read/Write)

The name of the Cisco IOS (Internetwork Operating System) file is c2600-i-mz.122-28.bin.

• The “c2600” means that this IOS image is for a 2600 series router. Other values which may appear here for different router platforms are listed below.

c1005 – For 1005 platform

c1600 – For 1600 platform

c1700 – For 1700 series platforms

c2500 – For 2500 series platforms

c2800 – For 2800 series platform

c2900 – For 2900 series platforms

c3620 – For 3620 platform

c3640 – For 3640 platform

c4000 – For 4000 series platform

c4500 – For 4500 and 4700 platforms

• The “i” indicates  that this is the IP routing version of the IOS.

Normal values which may appear here are

a – appn

a2 – atm

a3 – SNA switching

b – appletalk

c – communications servers etc

i – ip

j – enterprise

l – IPX

n – Novell

o – firewall

p – service provider

v – voice

• The “mz” indicates that this version of the IOS runs from RAM and the IOS file is compressed.

• The “122-28” indicates that this is IOS version 12.2, patch level 28.

 Posted By – RamCruiseWalker


Cisco Router Configuration Files

Cisco Router Configuration Files, startup-config, running-config, Start-up Configuration file, Running Configuration file

               Cisco Router configuration files hold the commands to configure the router. There are two main copies of Cisco Router configuration file. The configuration file where router stores the configuration changes when the router is up and running is called the “running-config” file. The running configuration file stores the configuration changes made while the router is up and running. The “running-config” file is stored in RAM. The “running-config” file is NOT persistent, which means that the changes made in the “running-config” while the router is running are not retained after a reboot. You can back up, or save, “running-config” file to either NVRAM or a TFTP (Trivial File Transfer Protocol) server.

A persistent copy of Cisco Router configuration file is called as “startup-config” file. The “startup-config” file is kept in NVRAM and the contents of the “startup-config” file are retained after a reboot. To save the changes of “running-config” file to “startup-config”, run the following IOS command.

OmniSecu03# copy running-config startup-config

The “running-config” can also be saved in a TFTP (Trivial File Transfer Protocol) server if you have a TFTP (Trivial File Transfer Protocol) server in your network. To save “running-config” file to a TFTP (Trivial File Transfer Protocol) server, run the following IOS command.

OmniSecu03# copy running-config tftp


Remember, “startup-config” is a persistent copy of configuration file, which is kept normally in NVRAM.


Configure Solarwinds Trivial File Transfer Protocol (TFTP) Server to backup IOS and configuration files

                  Solarwinds Trivial File Transfer Protocol (TFTP) Server is a free TFTP Server product from Solarwinds. After the installation of Solarwinds Trivial File Transfer Protocol (TFTP) Server in a computer, you need to configure it to backup IOS and configuration files of Cisco Routers and Switches.

Follow these steps to configure Solarwinds Trivial File Transfer Protocol (TFTP) Server

1) Make sure that the computer on which Solarwinds Trivial File Transfer Protocol (TFTP) Server is on the same network and the TCP/IP settings of the computer is on the same network where the router interface is connected. In our environment, the IP Address of the fa0/0 interface

If you want to configure the IP address for the routers fa0/0 interface, connect the router and follow these steps.

OmniSecuRouter01#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
OmniSecuRouter01(config)#interface fa0/0
OmniSecuRouter01(config-if)#ip address
OmniSecuRouter01(config-if)#no shutdown

To configure TCP/IP settings of the computer similiar as below. Here the IP address of the computer where Solarwinds Trivial File Transfer Protocol (TFTP) Server installed is

Solarwinds tftp server tcpip settings

Test the connectivity by pinging to the router.

Remember that the standard UDP port number for Trivial File Transfer Protocol (TFTP) is 69. Make sure that the firewall on the computer where Solarwinds Trivial File Transfer Protocol (TFTP) Server is installed is NOT blocking UDP port 69.

2) Run the Solarwinds Trivial File Transfer Protocol (TFTP) by clicking it from Start > Programs. Click menu File > Configure.

Solarwinds TFTP server configure menu

3) Start TFTP server by clicking the “Start” button and make sure the service is started by checking the status. Also verify the default root directory location of the TFTP Server.

Solarwinds TFTP server configure dialog box

Posted By – RamCruiseWalker


Install Solarwinds Trivial File Transfer Protocol (TFTP) Server

                              Many Trivial File Transfer Protocol (TFTP) server software products are available for free download on the Internet. Solarwinds Trivial File Transfer Protocol (TFTP) server is one of the leading free Trivial File Transfer Protocol (TFTP) server software. Click the following link to download Solarwinds Trivial File Transfer Protocol (TFTP) server. You need to register on Solarwinds web site to download the Solarwinds Trivial File Transfer Protocol (TFTP) server product.

After downloading the Solarwinds Trivial File Transfer Protocol (TFTP) server, complete the following steps to install and configure it.

Remember, these steps may vary depending on version.

1) Double click the setup file to run the Solarwinds Trivial File Transfer Protocol (TFTP) server installation wizard. Click “Next” to continue.

2) Click the “I accept the terms of the license agreement” radio button and click “Next” to continue.

3) Enter the customer information and click “Next” to continue.

4) Select the installation location and click “Next” to continue.

5) Click “Install” to start the installation of Solarwinds Trivial File Transfer Protocol (TFTP) server.

 Solarwinds TFTP server installation-install

6) Click the “Finish” button to complete the installation.

Posted By – RamCruiseWalker


Trivial File Transfer Protocol (TFTP)

Trivial File Transfer Protocol (TFTP) is a file transfer protocol, which is the basic form of File Transfer Protocol (FTP).

Trivial File Transfer Protocol (TFTP) has a very simple design and it requires only a very small amount of memory.

Trivial File Transfer Protocol (TFTP) is mainly used for network booting of computers and network infrastructure devices such as routers and switches.

Trivial File Transfer Protocol (TFTP) is used in Cisco networking environment to back up Cisco IOS (Operating System) image file, configuration files, Network Booting and for an IOS upgrade.

Trivial File Transfer Protocol (TFTP) is a simple file transfer protocol and it is implemented on top of the User Datagram Protocol (UDP). The standard UDP port number for Trivial File Transfer Protocol (TFTP) is 69.

Many Trivial File Transfer Protocol (TFTP) server software products for windows Operating System are available for free download on the Internet. Some are listed below.

Solarwinds Trivial File Transfer Protocol (TFTP) server

tftpd32 Trivial File Transfer Protocol (TFTP) server

Open Trivial File Transfer Protocol (TFTP) server

Posted By – RamCruiseWalker


Collision Domain and Broadcast Domain

Collision Domain

                                                A term collision is described as an event that usually happens on an Ethernet network when we use a “Shared Media” to connect the devices in an Ethenrnet network. A “Shared Media” is a type of connecting media which is used to connect different network devices, where every device share the same media. Example: 1) Ethernet Hubs, 2) Bus Topology

In a “Shared Media” there are no separate channels for sending and recieving the data signals, but only one channel to send and recieve the data signals.

We call the media as shared media when the devices are connected together using Bus topology, or by using anEthernet Hub. Both are half-duplex, means that the devices can Send OR Recieve data signals at same time. Sending and recieving data signals at same time is not supported.

Collisions will happen in an Ethernet Network when two devices simultaneously try to send data on the Shared Media, since Shared Media is half-duplex and sending and recieving is not supported at same time. Please refer CSMA/CD to learn how Ethernet avoid Collision.

Collisions are a normal part of life in an Ethernet network when Ethernet operates in Half-duplex and under most circumstances should not be considered as a problem.

A Collision Domain is any network segment in which collisions can happen (usually in Ethernet networks). In other words, a Collision Domain consists of all the devices connected using a Shared Media (Bus Topolgy or usingEthernet Hubs) where a Collision can happen between any device at any time.

Collision Domain

For Example, if “Computer A” send a data signal to “Computer X” and “Computer B” send a data signal to “Computer Y”, at same instance, a Collision will happen.

As the number of devices in a collision domain increases, chances of collisions are also more. If there is more traffic in a collision domain, the chances of collisions are also more. More collisions will normally happen with a large number of network devices in a Collision domain.

Increased collisions will result in low quality network where hosts spending more and more time for packet retransmission and packet processing. Usually switches are used to segment (divide) a big Collision domain to many small collision domains. Each port of an Ethernet Switch is operating in a separate Collision domain.

In other words, Collision cannot happen between two devices which are connected to different ports of a Switch.

No need to worry much about collision and related network problems now because we are not using Network Hubs to connect our devices. Ethernet Network Hubs are replaced with Ethernet Network Switches long way back.

Broadcast Domain

                                             Broadcast is a type of communication, where the sending device send a single copy of data and that copy of data will be delivered to every device in the network segment. Brodcast is a required type of communication and we cannot avoid Broadcasts, because many protocols (Example: ARP and DHCP) and applications are dependent on Broadcast to function.

A Broadcast Domain consists of all the devices that will receive any broadcast packet originating from any device within the network segment.

          In above picture, “Computer A” is sending a broadcast and switch will forward it to every ports and all the switchs will get a copy of broadcast packet. Every switch will flood the broadcast packet to all the ports. Router also will get a copy of broadcast packet, but the Router will not forward the packet to the next network segment.

As the number of devices in the Broadcast Domain increases, number of Broadcasts also increases and the quality of the network will come down because of the following reasons.

1) Decrease in available Bandwidth: Large number of Broadcasts will reduce the available bandwidth of network links for normal traffic because the broadcast traffic is forwarded to all the ports in a switch.

2) Decrease in processing power of computers: Since the computers need to process all the broadcast packets it recieve, a portion of the computer CPU power is spent on processing the broadcast packets. Normally a Broadcast packet is relevent to a particular computer and for other computers that broadcast packet is irrelevant (For example, DHCPDISCOVER message is relevent only for a DHCP Server. For other computers DHCPDISCOVER is irrelevant and they will drop the packet after processing). This will reduce the processing power of computers in a Broadcast domain.

By design, Routers will not allow broadcasts from one of its connected network segment to cross the router and reach another network segment. The primary function of a Router is to segment (divide) a big broadcast domain in to multiple smaller broadcast domains.

Posted By – RamCruiseWalker


Configuring And Testing The Network


In this chapter, we will learn how to configure the various internetwork devices such as the router and the switch. We will also cable the network correctly according to the requirements and learn the various   CISCO IOS – CISCO internetwork operating system basics that we will use throughout the course. As we mentioned in the beginning of the course, this will be a lab oriented course and therefore, you are expected to have lab equipment. If you do not have the physical devices, do not worry because we will discuss an alternative that can be used for learning purposes in this course.

Upon completion of this chapter, you will be able to:

  • Understand the role of the CISCO IOS
  • understand the config file on routers and switches
  • Understand the IOS command structure
  • Configure basic configuration of a router or a switch
  • Verify the configuration on a router using show commands.

    Internetwork operating system

    I am sure that you already know that computers have operating systems. The operating system allows the computer to function and also allows us to input and receive output. The operating system is the intermediary between us and the computer’s internal components. Similarly, the router also has an operating system.

    CISCO uses the IOS (internetwork operating system) to allow us to use the various capabilities in the routers.

    The CISCO IOS allows us to perform functions such as:

    • Routing
    • Security for the network
    • Expand the network based on requirements among others.

    Unlike other operating systems that you may be accustomed to however, the CISCO IOS is accessed using a CLI (Command Line Interface). If you have used programs such as DOS™ then you are familiar with the CLI prompt.

Access methods

The CLI on routers may be accessed using one of the following ways:

  • Console port
  • Auxiliary port
  • Virtual terminal lines.

There are several programs that we can use to access the CLI on routers.

  1. The console port is the main port that is used to configure a router. When the router is new and out of the box, this is the interface that is used to configure the router. After the initial configuration, we can use other configuration methods. The console port is also used for disaster recovery in case the router is unusable or as a way to troubleshoot the router when other connectivity means are unavailable.
  2. The second way we can configure a router is using an auxiliary port. The auxiliary port is used to configure the router through the use of a modem. This port is rarely used and as such we will not discuss its use further.
  3. The third way we can configure a router is by using the virtual terminal lines. As the name suggests, the virtual terminal lines are configured as a way to access the router remotely.

The administrator can configure the router to be accessed from a remote location using these lines.

In this course, we will learn how to configure the two types of VTY lines, either through telnet or the more secure SSL.

NOTE: the operation of the router depends on the commands that we issue during configuration as well as the IOS functioning.

Configuration files on the router

As mentioned earlier, the router is a computer and it the configuration we do determines its operation. The router has two types of memory; volatile and non-volatile memory. The configuration we make is stored in one of these two types of memory depending on the commands we issue.

There are two types of configuration files on the router.

The startup configuration file (startup-config) – this is the file that is used during the startup of the router. It is stored in the non-volatile memory which is called the NVRAM. The startup configuration consists of all the commands we have issued and saved in the router. Once the router boots up, this file is loaded from the NVRAM to the RAM where it is used as the running configuration file.

The running configuration the operation of the router is determined by the running configuration. Any command that we issue on a router is immediately executed and stored in the running- configuration. This file is stored in the RAM or the volatile memory. This means that if the router loses power, any unsaved changes in this file will be lost. When the running- configuration is saved, it is stored in the NVRAM and becomes the startup-config.


The CISCO CLI is structured hierarchically. The modes are executed from the top to bottom. Each mode gives access to certain commands that can be issued. The list below shows the CISCO IOS modes from the top to bottom.

  • User exec mode
  • Privileged exec mode
  • Global config mode
  • Other specific configuration modes

On gaining access to the router, there will be various prompts that will denote the specific level in which the administrator is in. however, the beginning of the prompt will be the router’s name. The various prompts are discussed below.

  1. User executive mode

This is the main or the first mode that one can access on a router. It is limited to few verification and troubleshooting commands. By default, authentication is not required but as best practice we will configure security so as to ensure protection of our routers.

On accessing the router, you will notice the prompt that ends with this symbol “>” after the router’s name. By default the name of the router is usually “Router“. This prompt is shown below.


In this mode, we can view basic information using the “show” command.

  1. Privileged executive mode

This is the second mode in the IOS CLI. In this mode, we can view various troubleshooting and verification commands such as “show and debug“. By default, this mode is also not secured, as best practice we will also secure this mode using a password.

This mode is denoted by the HASH (#) symbol preceeded by the name of the router. To enter this mode, we issue the command “enable” from the user exec mode.


NOTE: To move from the user exec mode to the privileged mode the command – “enable” should be entered from the user exec mode.

The “disable” command is used to exit the privileged exec mode and return to the user exec mode.

  1. Global configuration mode

The main configuration on a router is executed in this mode. Parameters such as the router’s name, ip domain lookup, banners among others can be configured. In this mode, we can also gain access to other specific configuration parameters such as interface configuration.

The global configuration mode is shown by the prompt: (config)# as shown below:


NOTE: To enter this mode from the privileged exec mode we enter the command: “Configure terminal”

To exit we to the privileged mode we enter the command: “exit”

  1. Specific configuration mode.

There are other specific configuration modes on the router. These are entered in the global configuration mode and are used to configure various functions and options on the router such as the interfaces, routing options, console lines among others. The specific configuration mode commands will be discussed progressively throughout the course.

commands format

When configuring the router, we need to understand the format used in configuration. The image below shows the IOS command structure.

We can also obtain help when typing a command we are unsure of in CISCO IOS. This is done by using a question mark “?” followed by the <enter> key. As shown in the image below.

We can use this command when we are unsure of the correct command to use or we have made an error.

We can also use the <tab> key to autocomplete commands. This may be useful when the command is too long and used frequently. However, we recommend that as we are beginning to learn the IOS, we should use the full command till at a later stage.

There are other shortcut keys used and these are shown below.

  1. Ctrl-R – to re-display a line
  2. Ctrl-Z – exit the configuration mode and returns the user to the user exec mode.
  • Down and up arrows – these are used to scroll through previously entered commands.
  • Ctrl-Shift-6 – this command is used to interrupt a command that has been issued.
  • Ctrl-C – this command can be used to abort a configuration line and return to the privileged mode.

There are other basics that are used in CISCO IOS, however, these we will learn as we continue in this course.

NOTE: you will be expected to know and memorize all the commands used in this course for the exam. In the ICND 1, ICND 2 and CCNA composite exams, the use of these commands will be frequent and you will NOT have anywhere to refer to.


Examination commands

When configuring a router, you may need to troubleshoot different configurations. The use of examination commands is vital in this respect. The examination commands are viewed in the privileged executive mode and will start with “show” in the prompt. Some of these commands and their functions are shown below.

  1. Show version – shows information on the CISCO IOS running on a router or a switch. Such as the version, release date.
  2. Show startup-config – this command shows the configuration file that is stored in the NVRAM.
  3. Show running-config – the commands that are currently being used by the router for its operation can be viewed using this command. This information is usually stored in the router’s RAM.

Network simulation using packet tracer

As mentioned earlier, access to physical network devices may at some times be difficult, and since this course is based mainly in a lab environment where we need to access and configure these devices, we need an alternative.

Your instructor should be able to give you access to packet tracer. A program that can be used to simulate networks in the lab environment. This software will give you access to most if not all, commands and devices needed in CCNA. In this course, we will use packet tracer and real devices in configurations.

After installation, the main window of packet tracer will be as shown below.

Familiarize yourself with the software. At the bottom left, we have the various categories of devices that may be used in the network. These include routers, switches, and connections among others. Clicking on any of these icons will bring a list of more devices in each category.

To use a device, simply click on its icon and drag it to the main work area shown in white.

On the right hand side, near the bottom, there are two icons in the shape of envelopes. These icons are used to capture packets and you will use them at a later stage. As you continue to use this software, you will become more and more experienced and gradually you will know all the capabilities and functions.

The scenario

In this chapter, we will configure 2 routers and 1 host PC in packet tracer. This will be basic configuration, aimed at showing you the main features of IOS and immersing you into the CISCO configuration environment using packet tracer.

The topology shown below shows 2 routers and a PC. The connection from the PC to router R1 is done using a crossover cable while the interconnection between the two routers is done using a serial cable.

The serial interface on R1 is the DCE side while the connection on router R2 is the DTE side. If you are using physical devices you should be aware of this cabling.

In this topology, we have 2 routers labeled R1 and R2. We have a connection between them which is S0/0/0 DCE on R1 and S0/0/0 on R2.

Router R1 is connected to PC A through 2 interfaces. One is the console port which will be used to configure the router, while the other will be the network port to PCA’s NIC via Fa0/0 on R1.

In packet tracer, the diagrams shown below are a guide to making this topology.


Drag and drop into the main work area the devices that will be used in the configuration as shown in the topology. In this case we use 2 1841 CISCO ISR routers. By default they are labeled Router0 and Router1. Also in the end device section drag and drop a PC icon, as shown in the diagram.


Click on the router0 icon. A new panel opens up and details the back panel of the router. At the top, there are three tabs – physical, config, CLI. In this case we are interested in the physical. This router, does not have a WAN connection interface as shown in the part highlighted by the red arrow. We need to install the WAN interface module on both routers so that we can interconnect them using serial links.

To do this, we have to shut down the router and look for the appropriate module on the left which can be used for serial WAN connections. To turn off the router, you need click the switch button shown by the blue arrow in the diagram above.


We need to add the correct WAN module. From the left to the panel on the right highlighted by the red arrow in the previous diagram. In this case and most other scenarios, we will be using the WIC-2T module highlighted in red. Drag and drop it to the empty space as shown above.

NOTE: the router goes off when the power button is switched. After installing the module you need to switch it back on.


Next we need to connect the devices with the correct cable. The connection from the PC to Router0 uses a crossover cable while the connection between the two routers uses a serial DCE cable. In the connections tab at the bottom make sure you use the correct cable.

To connect devices:

  1. Select a cable by clicking on it.
  2. Click on the device you want to connect to
  3. Choose the correct interface number
  4. Repeat process on the other end of the cable by dragging it to the opposite device and clicking on the correct interface.

These steps are shown in the diagrams below

The connections shown are for router0 and router1.


Connection on Router0 shown above using serial0/0/0

Connection on Router0 shown above using serial0/0/0

The connection on Router1 using serial0/0/0 there are two connections from PC0 to Router0. One connection shown by the black dotted line is the LAN interface on PC0’s fastethernet interface while the blue one is the console cable used to configure Router0 as shown below.

As you can see from the diagram above, the interface labels are visible. To enable this, go to options, then click on preferences and in the preferences tab select the option that says “always show device labels” as shown below marked by a red arrow.

The console cable connects to the RS 232 port on the PC and the console port on the router.

Now that we have interconnected the devices, we need to access the CLI interface on the router from the PC0.

To do this, we need to click on PC0’s icon. Whereby we will receive this output.

As mentioned earlier, packet tracer simulates the operation of different network devices, in we click on the desktop tab, we will see the same options as we would a physical computer.

In this tab, we have several options such as the ip address configuration, the terminal and command prompt among others. In this case we will use the prompt which will connect us to the routers CLI.

After clicking the terminal tab, leave the configurations options on default and click OK. This will connect you to the router in its boot-up process shown by the several “#” output.

After the boot-up process is complete, you should receive a command prompt shown below. Type in “no” and press enter.

After this prompt, we will enter the user exec mode. As we mentioned earlier, this is the first access point in the CISCO IOS CLI.

It is denoted by the output:


To enter the privileged configuration mode we should type in “enable” and enter. This will take us to the privileged executive mode denoted by the output shown below.


In this mode we can do various troubleshooting commands such as show and debug commands.

Next we need to access the global configuration mode so that we can begin our configuration. To do this, we need to type in:

“configure terminal” followed by ENTER. This will take us into the global configuration mode which is shown in the prompt output as:


NOTE: if you are using real devices, the steps followed should be the same, and the output received should not be different. However, if you need more information, contact your trainer.


In this section, we should configure the following.

  1. Hostname on router0
  2. Limit access to the router
  3. Configure banners
  4. Disable ip domain lookup
  5. Configure the interfaces
  6. Verify the configuration
  7. Test local network connectivity
  8. Document the network

The commands used will be done mainly from the global configuration mode on router0. We will not configure Router1 but the same concepts will be used. Keep this in mind.

Hostname on Router0

In the topology diagram, the first router was R1 not Router0, when naming routers, remember to only use alphanumeric symbols and the underscore only. There should be no space between the names because this will return an error.

To change a hostname of a router or a switch the command needed in the global configuration mode is:

Router(config)# hostname <NAME_OF_ROUTER>

The parameter shown in angle braces will be the name used on the router or switch.

In this scenario, In the global configuration mode on Router0, the command needed to change the name of this router from Router0 to R1 will be:

Router(config)#hostname <R1>

After entering this command, you should be able to see the change reflected immediately from:

“Router(config)# ” to “R1(config)#

Now with that command we have successfully changed the name of the router.

Limit access to the router

The next thing we need to do is to limit access to the router. We need to do this so as to strengthen the security. Every device should have locally configured passwords to limit access.

We have seen that the CISCO IOS is organized hierarchically. One of the reasons behind this is to enhance security. In this respect we need to configure security on our router. The passwords we will configure are to require authentications at various points on our routers. The passwords we will configure are:

  • the console line password – to limit connection to the router using the console port
  • the enable password – to limit access to the privileged Executive mode
  • enable secret password – to configure encrypted passwords to protect the privileged EXEC mode
  • VTY lines password – to protect access to the router via telnet
  1. Console line

We first need to secure the console lines. As we saw earlier, the console lines allow access to configuration of the router through the router’s console port. To do this, we need to access the console line in the global configuration mode.

The command to access the console line is:

Router(config)# <line console 0>

The first line is usually 0 as shown above. After entering this command, we will enter the specific configuration mode for the console line which is shown below:


From this mode, we need to enter a password and also a command to require authentication before accessing the console line. The commands needed to do this are:

Router(config-line)#password <cisco>

Router(config-line)# login

The first line specifies that the password for the console on this router is “cisco” and the second line – “login” states that for anyone to access this router, you will need to enter a password to access the CLI using the console port.

To verify this command, the next time someone tries to access this router after it is rebooted, they will be required to enter this password.

In this scenario, we will use the password “cisco123” and the commands needed on R1 will be

  1. Privileged exec mode – enable password

The privileged executive mode allows us to access the global configuration commands, therefore, it is important to secure this mode so as to limit access.

To do this, we need to configure the “enable password” on the router’s global configuration mode. This will require the use of a password to enter the privileged executive mode.

In the global configuration mode enter the following:

Router(config)#enable password cisco

The above command specifies that to be able to access the privileged access mode, the user has to enter the password cisco in the user exec mode.

On R1, we configure the password “cisco1” for the privileged executive mode using the following command.

R1(config)#enable password cisco1

To verify this command, enter the command “end” to return to the privileged exec mode, then enter the command “disable” to return to the user exec mode.

To login to the privileged exec mode on R1, you will be required to enter the password “cisco1”.

  1. Enable secret command

The use of the enable password, is not secure since the password is stored in the flash memory as plain text and it can be easily cracked. To enable a more secure password for the privileged exec mode, we use the enable secret command.

The enable secret command will create an encrypted password.

To enter this command on a router use the following command:

R1(config)#enable secret <cisco12>

This specifies that we should use an encrypted password of “cisco12

If we use this command on R1, it will override the enable password and replace it with the secure password. To do this on R1 enter the following command.

R1(config)#enable secret cisco12

  1. Vty lines

We also need to limit remote access to the router, the vty lines allow access to a router via Telnet. By default, many Cisco devices support five VTY lines that are numbered 0 to 4. A password needs to be set for all available vty lines.

To enable a password for the telnet lines, we need to enter the specific configuration mode for these lines. To do this, we enter the command shown below:

R1(config)#line vty 0 4

The above command specifies that we want to configure the 5 telnet lines on this router. After entering this command, we will enter the vty lines configuration mode shown by the prompt below.


In this mode, we can configure the password and require authentication when a user wants remote access to a router. The commands needed to accomplish this are:

R1(config-line)#password <telnet_password>


The commands above specify that this router should be configured with a password and should require authentication with said password for access.

On R1, to secure the vty lines using the password cisco1234, the commands needed to accomplish this will be:

  1. Encrypting Password Display

The commands that we have used to configure the passwords are insecure since the passwords are stored in plain text. To enhance the security of the passwords that we have configured, we use the command “service password-encryption“. When this command is executed, the plain text passwords will be encrypted. This means that they one cannot see the password in plain text from the running- config.

To configure this on router R1, enter the command shown below in the global configuration mode:

R1(config)#service password-encryption

This will ensure that no password can be viewed from the running configuration.

Configure banners

Configuring passwords is a good measure to protect the router from unauthorized access. However, we also need to warn would be attackers.

Banners are a way in which we notify unauthorized personnel who would want to access the router. In some cases, failure to apply banners can cause attackers to escape legal ramifications since they can argue that there was no information against unauthorized access.

One way to configure the banner is using the MOTD (message of the Day). To do this, we need to enter the command shown below in the global configuration mode:

R1(config)#banner motd <# insert message in here #>

The # in the banner motd command denotes the beginning and end of the message to be displayed.

On R1, to configure a banner that states “!!!! WARNING, AUTHORIZED ACCESS ONLY!!!!” the command shown below will be used.

R1(config)banner motd #!!!! WARNING, AUTHORIZED ACCESS ONLY!!!! #

Once the command is executed, the banner will be displayed on all subsequent attempts to access the device until the banner is removed.

Configure the interfaces

In this scenario, there are 2 interfaces on R1 and 1 on the PC0 that we need to configure. The addressing scheme used is shown below.

Device Interface Ip address Subnet mask Default gateway
PC0 FastEthernet
R1 FastEthernet0/0

We will not configure Router1. When configuring the PC, the following steps should be taken:

  1. Click on the PC0 icon
  2. Click on the desktop tab
  3. Click on the ip configuration tab
  4. Enter the values shown above
  5. Close the ip configuration tab

On the router, we need to configure the interfaces and also activate them. By default, interfaces on routers are usually deactivated.

To configure the interface on a router, the following commands will be used.

Router(config)#interface <interface_name><interface_number>

Router(config-if)#ip address <interface_ip_address> <subnet_mask>

Router(config-if)#no shutdown


  • In the above configuration, the first line is used to enter into the specific interface configuration mode. This will allow us to enter various interface configuration options.
  • The second line will assign the ip address and the subnet mask according to the specifications
  • The third line will activate the interface and make it usable.

In this scenario, we have 2 interfaces on R1. To configure R1’s FastEthernet0/0 interface, the following commands will be used:

To configure the serial interface the following commands will be used.

As you can remember, we connected the router R1 using a serial DCE cable, this means that this interface must have a clocking signal simulated as you would using a CSU/DSU. The command:

Clock rate 64000 above, specifies that this interface is the DCE side and it has a clock rate of 64000.

In packet tracer, after configuring the interfaces and executing the “no shutdown” command, the end points on the fast Ethernet link from the PC0 to R1, should turn from red to green as shown in the figure below:

Verifying the configuration

After all these configurations are done, we need to verify that they have been executed as well as save the configuration to the NVRAM from the RAM.

To save the configuration, we need to exit to the privileged executive mode and enter the following command:

Router#copy <running-config> <startup config>

The command above when executed will save the running configuration to the NVRAM of the router, this will make the running configuration the startup-configuration in the next boot-up of the router.

On R1, the command needed to save the running configuration to the flash memory will be as shown below.

R1#copy running-config startup-config

After saving the configuration, we also need to verify the operation of the router, as well as check for connectivity to our host PC.

The verification commands we will use will also be used when troubleshooting. More on troubleshooting will be discussed in subsequent chapters.

In this chapter, we will check for the interface configuration, the running configuration, and the connectivity to the PC using ping command.

The running-configuration

After configuring the router, we need to check all the configurations used, to do this we need to check the running configuration. The running configuration as we mentioned earlier is stored in the RAM and therefore, any additional commands we make will need to be saved to the startup configuration.

The running configuration will show us all the commands that we have used while configuring a device.

The command used to check the running configuration is executed in the privileged executive mode and it is shown below.

router# show running config

When executed, this command will show us all the configuration commands used on a router or a switch.

The output of the show running-config on R1 is shown in the exhibit below:

Verify interface operation

When verifying the interfaces on routers, we need to check whether they are operational and whether they have been assigned the correct ip addresses. To accomplish this, we will use the commands shown below in the privileged executive mode:

  • Show ip interface brief
  • Show interface <interface name> <interface number>

Show ip interface brief

The output of this command will show the operational status of an interface at layer 1 and layer 2. The output shows the interface, the ip address assigned, the status, and the status of the protocol which is connectivity at layer 2. If the interface is operational, the status and protocol should be up/up.

Show interface <interface name> <interface number>

The output of this command shows the status of the specific interface as shown in the output below for interface FastEthernet 0/0.

As you can see from the above output, the interface is shown as on and it is operational. This is another way we can verify the status of an interface.


In this chapter, we have looked at the basic configuration in CISCO IOS. We have configured a router in packet tracer given the requirements of the lab. We have also looked at the command structure of IOS. In the next chapter, we will begin routing by looking at how routing works and configuration of static routes.


                                           Posted By – RamCruiseWalker


Connecting To Cisco Device

Planning And Cabling To The Network


                                        There are many considerations to make when planning the network. In this section we will consider the LAN connections and the WAN. The choice of which router to deploy is determined by the Ethernet interfaces that match the technology of the switches at the center of the LAN. The internetwork devices that we will be using in this course will be primarily routers and switches.


                                      The routers in our networks are used to interconnect the various LAN networks. Each LAN is usually connected to others using an interface on the router. The router has various LAN interfaces that it connects to these segments. Therefore, when choosing a router, you should consider the number of LANs in your global network. The router should also have interfaces that connect to outside interfaces such as to an ISP.

The figure shown below shows the various ports that can be found on a router as well as explanations on their use.

Image result for cisco router port specification

  • The fast Ethernet interface will be used to connect to our LAN networks while the serial interface will be used to connect to the WAN.
  • The console port is the main configuration port on a router, and it is where we will connect to the router and issue configuration commands through. The auxiliary port shown as aux port is used as an alternative to the console port.
  • The power button on a router is used to turn on and off the router.


The switch will be used to connect to the various end user devices in our network. These may be PCs, notebooks, IP phones among others. The switch is connected to the router using one of its interfaces so that other networks can be reached through the router.

The image shown below shows a 48 port CISCO switch.

Device selection factors

In our networks, there are several factors that will affect which devices we will install. These factors may affect network performance and may be influenced by the factors shown below.

Cost – the various models of CISCO routers and switches, the choice of router or switch may be influenced by the budget that the organization may have.

The speed of the ports on a device may influence the decision to install a particular device. We will learn about the various speeds and how they influence the network performance in upcoming chapters.

Other factors that may influence our choice of device are the manageability of a device, support, durability, whether it has expansion bays, among others.

Whatever device is chosen for your network, however, the successful implementation of the network will depend on the configuration and careful planning that has been done.

Cabling The Network

Cabling factors

When cabling the network there are several factors to consider.

  • The length of the cable
  • Telecoms room
  • Backbone and distribution cabling
  • Environmental factors

The length of the cable is one of the most important factors to consider. In most networks we will use the UTP (Unshielded Twisted Pair) cable. This cable is made of copper the range should be limited to 100 meters.

Telecommunications room – in many organizations, this is the central area where intermediary devices such as routers, backbone switches, among others are located. The cabling in this room should be correctly labeled so as to avoid misconfiguration and other problems.

Backbone cables are the cables used to connect to devices such as servers, distribution cables connect to end user devices and are mainly straight through UTP cables.


When cabling the network, there are several types of cables that may be used. We will discuss the use of the UTP cable and the serial cables.

UTP cable

The UTP cable will be used to connect the following devices

  1. Router to router – depending on scenario
  2. Router to switch
  3. Router to PC – or other hosts end devices
  4. Switch to switch
  5. Switch to hosts.

These configurations use three main types of UTP cable configurations which are.

  • Straight through
  • Cross over
  • Rollover cable

TIA/EIA governs the UTP cabling standards, the figure below shows an example of the UTP cable. It has four pairs of cables with different color codes.

There are 8 wires in pairs. These are

  1. Blue
  2. White+blue
  3. Orange
  4. White+orange
  5. Green
  6. White+green
  7. Brown
  8. White+brown

The two T568 standards i.e T568A and T568B, determine the arrangement of these wires so as to suit the various configuration needs.

T568A and T568B arrangements are shown in the image below.

Image result for ethernet cable color code

These configurations are constant and cannot change.

  1. Straight through configuration – both sides of the UTP cable have the same standard i.e both are either T568A or T568B.
  2. Crossover cable configuration – one end is T568A the other end T568B.

Where to use these cables

The straight through cable is used to connect devices that work on different layers of the OSI models. i.e

  • Routers and hosts such as PCs work on layer 3 – logical addressing
  • Switches work on layer 2 – physical or MAC addressing

Therefore, to interconnect a router to a switch or a switch to a PC, we use a straight through cable.

To interconnect devices working on the same layer in the OSI model, we use crossover cables. Ie – switch to switch, router to router and router to PC.

The table below shows the various connections used in the LAN using these standards.

Device 1 Device 2 Cable type
Router Router Crossover cable
Router Switch Straight through cable
Router PC Crossover cable
Switch Router Straight through cable
Switch PC Straight through cable
Switch Switch Crossover cable

Posted By – RamCruiseWalker

IPv4 Addressing

IPv4 Addressing Mode

IPv4 supports three different types of addressing modes.:

Unicast Addressing Mode:

In this mode, data is sent only to one destined host. The Destination Address field contains 32- bit IP address of the destination host. Here the client sends data to the targeted server:


Broadcast Addressing Mode:

In this mode, the packet is addressed to all the hosts in a network segment. The Destination Address field contains a special broadcast address, i.e. When a host sees this packet on the network, it is bound to process it. Here the client sends a packet, which is entertained by all the Servers:


Multicast Addressing Mode:

This mode is a mix of the previous two modes, i.e. the packet sent is neither destined to a single host nor all the hosts on the segment. In this packet, the Destination Address contains a special address which starts with 224.x.x.x and can be entertained by more than one host.


Here a server sends packets which are entertained by more than one servers. Every network has one IP address reserved for the Network Number which represents the network and one IP address reserved for the Broadcast Address, which represents all the hosts in that network.

Hierarchical Addressing Scheme

IPv4 uses hierarchical addressing scheme. An IP address, which is 32-bits in length, is divided into two or three parts as depicted:

IP Addressing

A single IP address can contain information about the network and its sub-network and ultimately the host. This scheme enables the IP Address to be hierarchical where a network can have many sub-networks which in turn can have many hosts.

Subnet Mask

The 32-bit IP address contains information about the host and its network. It is very necessary to distinguish both. For this, routers use Subnet Mask, which is as long as the size of the network address in the IP address. Subnet Mask is also 32 bits long. If the IP address in binary is ANDed with its Subnet Mask, the result yields the Network address. For example, say the IP Address is and the Subnet Mask is then:

IP Subnet Mask

This way the Subnet Mask helps extract the Network ID and the Host from an IP Address. It can be identified now that is the Network number and is the host on that network.

Binary Representation

The positional value method is the simplest form of converting binary from decimal value. IP address is 32 bit value which is divided into 4 octets. A binary octet contains 8 bits and the value of each bit can be determined by the position of bit value ‘1’ in the octet.

Binary RepresentationPositional value of bits is determined by 2 raised to power (position – 1), that is the value of a bit 1 at position 6 is 2^(6-1) that is 2^5 that is 32. The total value of the octet is determined by adding up the positional value of bits. The value of 11000000 is 128+64 = 192. Some examples are shown in the table below:

IP Bit Patterns

IPv4 Addressing

Addressing of IPv4


                                     In the previous chapter, we looked at the network layer and its involvement in communication. in this chapter, we will look at ipv4 addressing. This is one of the most important concepts in networking and will be critical in your overall success in networking. Understanding this chapter is critical to the rest of your studies.

                                    Internet Protocol version 4 (IPv4) is the fourth version in the development of the Internet Protocol (IP) and the first version of the protocol to be widely deployed. IPv4 is described in IETF publication RFC 791 (September 1981), replacing an earlier definition (RFC 760, January 1980).

IP – Internet Protocol

  • IP has two types
                                                                1. Internet Protocol Version –  4
2. Internet Protocol Version  – 6

It is a Connection less Protocol

IP Address : Numbers are Seprated By Dot


IP Address : 192.168.100. 101

Every IPv4 is consist of Four Octet

octet means group of eight bit


Every IP has Two Information field

  1.  Network Field

  2.  Host Field

IP Address has 5 classes :

  • Class A  =  1     – 126
  • Class B  =  128 – 191
  • Class C  =  192 – 223
  • Class D  =  224 – 239
  • Class E  =  240 – 255

Class Of IP Address decided by First Octet

CCNA would be only deciding with Class A,B,C

Class D is used for Multi-cast

Class E is Reserved For Experimental  Purpose

More Than 255 decimal number is Invalid Ip

Addressing Classes – IPv4

The first octet referred here is the left most of all. The octets numbered as follows depicting dotted decimal notation of IP Address:


The number of networks and the number of hosts per class can be derived by this Formula:


When calculating hosts’ IP addresses, 2 IP addresses are decreased because they cannot be assigned to hosts, i.e. the first IP of a network is network number and the last IP is reserved for Broadcast IP.

Class A Addressig

1 –  Network field 

3 – Host Field

Ex :                                    ( 1- 126 = class A)

The first bit of the first octet is always set to 0 (zero). Thus the first octet ranges from 1 – 127, i.e.

Class A Addresses

Class A addresses only include IP starting from 1.x.x.x to 126.x.x.x only. The IP range 127.x.x.x is reserved for loopback IP addresses.

The default subnet mask for Class A IP address is which implies that Class A addressing can have 126 networks (27-2) and 16777214 hosts (224-2).

Class A IP address format is thus:   0NNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHHH

Class B Addressing

2 – Network Field

2 – Host Field

Ex : 172.123.100 225                                  ( 128 – 191 = Class B)

An IP address which belongs to class B has the first two bits in the first octet set to 10, i.e.

Class B Addresses

Class B IP Addresses range from 128.0.x.x to 191.255.x.x. The default subnet mask for Class B is 255.255.x.x.

Class B has 16384 (214) Network addresses and 65534 (216-2) Host addresses.


Class C Addressing

3 – Network field

1 – Host Field

Ex :                                            (192 – 223 = Class A)

The first octet of Class C IP address has its first 3 bits set to 110, that is:

Class C Addresses

Class C IP addresses range from 192.0.0.x to 223.255.255.x. The default subnet mask for Class C is 255.255.255.x.

Class C gives 2097152 (221) Network addresses and 254 (28-2) Host addresses.


Class D Address

Very first four bits of the first octet in Class D IP addresses are set to 1110, giving a range of:

Class D Addresses

Class D has IP address rage from to Class D is reserved for Multicasting. In multicasting data is not destined for a particular host, that is why there is no need to extract host address from the IP address, and Class D does not have any subnet mask.

Class E Address

This IP Class is reserved for experimental purposes only for R&D or Study. IP addresses in this class ranges from to Like Class D, this class too is not equipped with any subnet mask.

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Communicate With Router

Communicate With Router

Communicate with a Router using Console, Auxiliary, Telnet, SSH, HTTP and HTTPS connections

                            Routers are special computers built to handle internetwork traffic. Routers are very important network infrastructure devices and they serve many users at same time. The end users ho not communicate with the routers, but the network traffic generated by the end users communicate through the router.

                      There are no input devices for router like a monitor, a keyboard, or a mouse. An administrator can choose any of the following methods to communicate with the router.

Connection by using Console Port:

                            By connecting the router’s console port to a workstation through a console cable. The console port is the management port which is used by administrators to log into a router directly-that without using a network connection. You require a terminal emulator application like Hyperterminal or PuTTY to connect to router. Console port connection is a way to connect to the router when a router cannot be accessed over the network.  

Connection by using Auxiliary Port (AUX Port):

                         By using a remote computer through a modem that calls another modem connected to the router with a cable using the Auxiliary Port on the router. Auxiliary Port (AUX Port) allows a direct, non-network connection to the router, from a remote location. The Auxiliary Port (AUX Port) uses a connector type to which modems can plug into, which allows an administrator from a remote location to access the router like a console port.

Connection by using protocols like telnet, SSH, HTTP or HTTPS:

                          The routers can be managed over the network by using standard TCP/IP protocols like Telnet, SSH, HTTP or HTTPS. Telnet was developed in the early days of the UNIX operating system to manage computers remotely. A Telnet client and server application ships with Cisco’s IOS software and most computer operating systems. SSH is a more secure way to configure routers, since the SSH communication is encrypted. Cisco IOS also has a HTTP server to managed web based communication with the router.
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TCP/IP And OSI Model

         TCP/IP and the OSI Model


                      In the previous chapter we were introduced to computer networks and we got to know their importance in everyday lives. In this chapter, we will look at the layered models that are used in communication over networks.


Layer Models

To better understand the various protocols and how they work with each other, we use layered models. A layered model shows how the protocols work at each layer as well as how the layers interact with the layers either above them or below them. The layered models that are used in modern computer networks are two; the OSI model (Open Systems Interconnection) and the TCP/IP model (Transmission Control Protocol/ Internet Protocol)

 There are several benefits that to using the OSI and TCP/IP models in explaining how network protocols work and these include the following.

  • Each layer in a model defines different protocols, therefore by using a layered model, network engineers can be able to define and design protocols which conform to the specific layer.
  • Competitions between different vendors is increased, this is because the models define standards and therefore product superiority is not based on the use of certain protocols since all products support them.
  • The layered model is useful since it allows for independence between other layers. This means that if a change in technology or capabilities is made in one layer, it will not affect another layer either above it or below it.
  • Since the layered model is an open standard, it provides for conformity and interoperability between different networking devices.

OSI Model

The OSI model provides an extensive list of functions and services that can occur at each layer. It also describes the interaction of each layer with the layers directly above and below it.

TCP/IP Model

                                        This model was first introduced in the 1970’s. There are four categories as you can see from the output above. Network communications were first defined using this model and for successful communication to occur, the functions of each layer must be in place in a network.

     From the output below, you can see the function of each and every layer of this model. The application layer, is the component that interfaces with the user, when you are using a web browser, this is a component of the application layer

The transport layer defines the various ports and helps differentiate the different types of communication from a single user. You may be sending an email, browsing and listening to internet radio on one computer. It is the work of the transport layer to differentiate the different types of communications. The transport layer also helps in interoperability between different network devices such as a PDA and a computer.

 The internet layer is meant to provide the best path to remote networks, this differentiates the different devices on a network. If a message is to be sent from one computer to another on a remote network, it is the work of the internet layer to make sure the message gets to the intended recipient. You may compare the internet layer to an address you use when you want to send a letter.

  The network access layer acts as an interface between the hardware and software components in the network. The application, transport and internet layers are all implemented by software, however, the network access translates the messages from these layers to a form that can be transmitted over various media such as fiber optic cables, copper wire and wirelessly.

 The protocols that are defined in the TCP/IP model describe the various functions and processes at each layer. This means that the protocols at each layer have to have specific functions as described by the TCP/IP model.


1. At the application layer, we would create the email and this would be the data that would be communicated over the network.

2. The transport layer would then break this data into segments and add information in a process known as encapsulation.

3.The segments would then be passed down to the internet layer and encapsulated into packets, in this layer, logical addressing would be added. (more on logical addressing will be discussed later)

4.The packets would then be passed to the network access layer, the network access layer would then prepare the packets for transmission over the physical media such as fiber optic cable by converting the data to light signals.

5.When the data is received at the destination, the reverse process would happen, i.e., removal of protocol specific information – decapsulation as well as reassembly into the application data would be carried out.

6.The data would then be passed to the user. This process is illustrated below.

TCP/IP and OSI Model

  1. Data – the end user information, this may include, email content, website information among others. This is the information presented to the user.
  2. Segment – as mentioned earlier, this is the PDU at the transport layer.
  3. Packet – in the internetwork layer, the packets are the PDUs and they include the logical addressing for remote delivery.
  4. Frame – this is the form that data at the network access layer takes, there is also addressing at this layer which is physical addressing such as the MAC address.
  5. Bits – the form that is carried over the physical media form is Bits, these may be in many forms such as electrical signals, light signals and others.

PDUs and communication over a layered mode

The OSI model defines how messages are encoded, formatted, encapsulated, and segmented so that they can be transmitted over networks. As we mentioned earlier, the data is usually broken down into different PDUs and the layers in the OSI model define how each PDU is controlled so as to make communication successful.

Addresses are one of the ways that communication is made successful in the network. If we can use the post office analogy, you can imagine how difficult it would be if not impossible to send letters without a destination address or how difficult it would be if the recipient would not know who to reply to. The diagram below shows the various addresses that are used in communication over the network.


                               In this chapter, we have discussed how communication works over the layered model. We have looked at the TCP/IP and OSI reference models and how they define communication at each layer. We have also looked at the protocol data units and compared the two models. In the next chapter, we will look at the application layer.

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Different Types Of Router Memory, Introducion

Different Types Of Router Memory


Different Types Of  Router Memory



               ROM is read-only memory available on a router’s processor board. The initial bootstrap software that runs on a Cisco router is usually stored in ROM. ROM also maintains instructions for   Power-on Self Test (POST) diagnostics. For ROM Software upgrades, the plugable chips on the motherboard should be replaced.
Flash Memory

                                         Flash memory is an Electronically Erasable and Re-Programmable memory chip. The Flash memory contains the full Operating System Image (IOS- Internetwork Operating System). This allows you to upgrade the OS without removing chips. Flash memory retains content when router is powered down or restarted.


            RAM is very fast memory that loses its information when the router is shutdown or restarted. On a router, RAM is used to hold running Cisco IOS Operating System, IOS system tables and buffers RAM is also used to store routing tables, keep ARP cache, Performs packet buffering (shared RAM). RAM Provides temporary memory for the router configuration file of the router while the router is powered on.

RAM Stores running Cisco IOS Operating System, Active program and operating system instructions, the Running Configuration File, ARP (Address Resolution Protocol) cache, routing tables and buffered IP Packets.

NVRAM (Non-volatile Random Access Memory)

              NVRAM is used to store the Startup Configuration File. This is the configuration file that IOS reads when the router boots up. It is extremely fast memory and retains its content when the router is restarted.


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CCNA -Introduction

The Networking World

CCNA :Cisco


CISCO Certified CCNA

The CCNA certification has been devised by CISCO and stands for Cisco Certified Network Associate. The certificate validates a professional’s ability to understand, configure, operate, configure and troubleshoot medium-level switched and routed networks and also includes the verification and implementation of connections via remote sites using WAN.


Communication has evolved greatly. Traditional communication methods such as mail have been overtaken by more sophisticated forms. Electronic Communication methods offer higher speeds; more efficiency, reliability, integrity, security; scale across larger geographical areas and require less resources to use. Tools and services such as e-mail, blogs, podcasts, instant messaging, and social networks among other multimedia methods have changed the way we communicate to a great extent.

In this chapter, we give an overview of the world of networks: we will discuss the following:

  1. The role of networks in our lives
  2. Explain the qualities and elements of a network
  3. Define key terms and diagrams used in this course
  4. Explain what a converged network is
  5. Give a brief history of computer network

Elements of a network

In order to understand networks we need to understand the elements of a network. There are four main elements that define how communication over networks works.

  • Rules or agreements to govern how the messages are sent, directed, received and interpreted – examples include protocols.
  • The messages or units of information that travel from one device to another – these may be packets, frames among others.
  • A means of interconnecting these devices – a medium that can transport the messages from one device to another – such as copper cables, fibre optic among others.
  • Devices on the network that exchange messages with each other – these may include ip phones, computers, servers, routers among others.

Cisco Certificate

Certification Track

CCNA Job-Role Salary


Cisco – Router

Cisco – Switch

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Router interface naming convention

Cisco Routers different types of interfaces like Serial, Ethernet, Fast Ethernet, Gigabit Ethernet, Tokenring,  FDDI are some of them (A single router may not have all these). The speed of Ethernet, Fast Ethernet and Gigabit Ethernet are different. The speed of Ethernet is 10 Mbps (Megabits per second), Fast Ethernet is 100 Mbps (Megabits per second) and Gigabit Ethernet is 1 Gbps (Gigabits per second)

Most of the latest routers are modular routers. Modular routers are expandable routers by using plug-in components.

The following naming convention is followed for a Cisco Router.


Slot numbers begin with 0 and port numbers begin with 0. Hence the name of the first interface of a WIC2T (modular card with two smart serial interfaces) is serial0/0 and the name of the second port is serial0/1. The short form of the two interface is s0/0 and s0/1.

Old 2500 series routers are not modular, and they had fixed ports. The interface naming convention of these routers is

<Interface_Type>< Port_Number>

Hence the name of the first Ethernet interface for non-modular router is ethernet0 or e0, and first Serial interface is serial0 or s0.


Difference Between Routing Protocols and Routed Protocols

Routed Protocols

A Routed Protocol is a network protocol which can be used to send the user data from one network to another network. Routed Protocol carries user traffic such as e-mails, file transfers, web traffic etc.

Routed protocols use an addressing system (example IP Address) which can address a particular network and a host (a computer, server, network printer etc) inside that network. In other words, the address which is used by a Routed Protocol (Example IP (Internet Protocol)) has a network address part and a host (a computer inside a network) part.

IP (Internet Protocol) is the most widely used Routed Protocol. Internet is using IP (IPv4 or IPv6) as its Routed Protocol. Other Routed protocols are vanishing from network industry.

A Routed Protocol is an integral part of network protocol suit and it is available in every device which is participating in network communication (Example, Routers, Switches, Computers etc).

Routing Protocol

A Routing Protocol learns routes (path) for a Routed Protocol and IP (Internet Protocol), IPX (Internetwork Packet Exchange) and Appletalk are the examples of Routed Protocols.

Routing Protocols are network protocols used to dynamically advertise and learn the networks connected, and to learn the routes (network paths) which are available. Routing protocols running in different routers exchange updates between each other and most efficient routes to a destination. Routing Protocols have capacity to learn about a network when a new network is added and detect when a network is unavailable.

Routing Protocols normally run only in Routers, Layer 3 Swithes, End devices (firewalls) or Network Servers withNetwork Operating Systems. Routing Protocols are not available in a normal computer or a printer.

Examples of Routing Protocols are RIP (Routing Information Protocol) , EIGRP (Enhanced Interior Gateway Routing Protocol) and OSPF (Open Shortest Path First).

Following table lists important Routing Protocols related Routed Protocols.

Routed Protocol Routing Protocols

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Difference Between Static Route and Dynamic Route

Routing is the process of selecting paths in a network along which to send network traffic and route is the path to send the network traffic.

There are two ways a router learn a route: static and dynamic. The difference between static route and dynamic route is as below. A static route is a route that is manually configured on the router. Simply we can say a static route is a route that is created manually by a network administrator. The information about the networks that are directly connected to the active router interfaces are added to the routing table initially and they are known as connected routes. The second way that the router can learn static routes are by configuring the routes manually.

Dynamic routes are routes that a router learns by using a routing protocol. Routing protocols will learn about routes from other neighbouring routers running the same routing protocol. Dynamic routing protocols share network numbers a router knows about and how to reach these networks. Through this sharing process, a router can learn about all of the reachable network numbers in the network.

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