Configure Router Serial Interfaces, DTE (Data Terminal Equipment) and DCE (Data Communications Equipment)

When connecting a serial cable to the serial interface of the router, clocking is provided by an external device, such as a CSU/DSU device. A CSU/DSU (Channel Service Unit/Data Service Unit) is a digital-interface device used to connect a router to a digital circuit. The router is the DTE (Data Terminal Equipment) and the external device is the DCE (Data Communications Equipment), where the DCE provides the clocking. However, in some cases we might connect two routers back-to-back using the routers’ serial interfaces (Example: Inside the router labs). Each router is a DTE by default. The cable decides which end to be DCE or DTE and it is usually marked on the cable. The picture below shows back to back cable.

Smart Serial to Smart Serial back to back cable

If is not marked, we can use the Cisco IOS show command “show controller” command to determine the interface is DTE or DCE. Since clocking is required to enable the interface, one of the two routers should function as DCE and should provide clocking. This can be done by using the “clock rate” command, from the interface configuration mode.

To find the possible clock rate values, get the command help by using a question mark after the “clock rate” from the serial interface configuration mode, as shown below.

Router(config-if)# clock rate ?

The output for above command is shown below.

R1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#interface serial 1/0
R1(config-if)#clock rate ?
With the exception of the following standard values not subject to rounding,

          1200 2400 4800 9600 14400 19200 28800 38400
          56000 64000 128000 2015232

  accepted clockrates will be bestfitted (rounded) to the nearest value
  supportable by the hardware.

  <246-8064000>    DCE clock rate (bits per second)

These values are in bites per second. You can find the possible values by using help.

Router(config)# interface s0/1
Router(config-if)# clock rate 64000

All interfaces have a bandwidth value assigned to them. This is used by certain routing protocols, such as IGRP,OSPF, and EIGRP, when making routing decisions.

For LAN-based interfaces, the speed of the interface becomes the bandwidth value (In kilobits per second (Kbps)). However, on synchronous serial interfaces, the bandwidth defaults to 1,554Kbps and this is not related with the clock rate set. To change the bandwidth value for an interface, use the bandwidth Interface Subconfiguration mode command:

Router(config)# interface  s0
Router(config-if)#bandwidth 64


Posted By – RamCruiseWalker


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


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

Communicate With Router

Connect and Access a Router or Switch

How to Connect and Access a Router or a Switch using Console connection

                       Every Cisco router or a switch has a console port (also known as the management port) on its back side.  Console port is used to connect a computer directly to a router or switch and manage the router or switch since there is no display device for a router or switch . The console port must be used to initially to install routers onto because there is no network connection initially to connect using SSH, HTTP or HTTPS. Normally router console port is a RJ45 port. The following picture shows a console port on a router.

        * The Console Port has to be Blue Color of all Router and Switch



A special type of cable, known as roll over cable is used to connect the Serial/COM port of the computer to the router or switch console port. One end of the cable is RJ49 type and a DB9 to RJ45 converter is molded on the other end. A picture of the console cable is shown below.


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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.
Posted By – RamCruiseWalker