CCNA Study Guide

This tutorial explains color coding standards for cross cable and straight cable including general guideline for cabling Cisco devices.

Without configuration Routing device is a driverless car. It is expensive, adorable but without driver it is useless. Think configuration as driver of Routing device. Configuration guides it to take proper action. Routing device does not have any display interface. You have to connect it with PC, tablet , laptop or other device in order to configure it.

Connecting cisco devices

Cisco makes a lot of devices, from those in this article we will discuss only the devices which are covered in CCNA exam. Whenever we will use word "Cisco device" in this article, take that for router, switch and PC collectively.

Router

A router supports many interface among those Serial, Ethernet and console are the must have interface. Every router has at least these interfaces.

Serial interface

Serial interface connects router with wan network. In wan network, communication takes place between two types of device DTE and DCE.

DTE

DTE is an end device. It stands for Data Terminal Equipment. It ends communication line. It converts data in signal and vice versa.

DCE

DCE stands for Data Communication Equipment. It provides a path for communication.

For example you want to access a website. For it you have to connect the computer with Internet through the modem. Modem will connect PC with ISP. ISP will make connection with hosting server.

DCE and DTE Devices
  • In this example PC and Server are the DTE, as both ends communication line.
  • Two modems (yours and providers) are DCEs, as they make the communication between you and provider

The COM port on a PC is a DTE port.

The COM ports on modems are configured as DCE port.

Any device that connects to a computer's COM port using a straight through serial cable is a DCE device.

Remember

  • DCE: Provides clock rate
  • DTE: Receives the clock rate
  • Clock Rate: Speed of data transmission

In job environment, when you connect serial cable to the serial interface of router, most probably other end of cable would be connected to CSU/DSU device. A CSU/DSU (Channel Service Unit/Data Service Unit) device connects router with digital circuit (Wan Network). By default all Cisco routers work as DTE. In this situation clocking is provided by CSU/DSU device.

In lab environment, we usually connect two routers back to back using serial interface. As we know that all routers are configured by default as DTE device. We have to change one serial interface as DCE. Serial cable decides which end would be DCE or DTE. It is usually marked on the cable.

DCE DTE Serial cable

Some time it is not marked on cable, still you can determine the interface. For that you have to use "show controller" command from privilege exec mode.

show controller

Third line of output will tell us whether connected side of cable is DCE or DTE.

Ethernet interface

Ethernet interface is used to connect local network to router, PC to switch, switch to switch, switch to router. Ethernet interface uses UTP cable for connection. UTP (Unshielded twisted pair) cable has four pairs of wires twisted inside it.

UTP Cable

UTP cable used for

  • Ethernet connections
  • Serial connections
  • Console connections
  • ISDN (Integrated Service Digital Network) connections
  • Modular and fixed interface connections

Different type of connections need different type of configuration including

  • Straight-through
  • Crossover
  • Rollover

Straight-Through Cable

Straight-through cable is used to connect DTE to DCE devices. It has same pin assignments on each end.

Side ASide B
Green WhiteGreen White
GreenGreen
Orange WhiteOrange White
BlueBlue
Blue WhiteBlue White
OrangeOrange
Brown WhiteBrown White
BrownBrown
Straight Cable

A straight-through cable connects

  • PC to Switch
  • PC to Hub
  • Router to Switch
  • Switch to Server
  • Hub to Server
Use of Straight cable

Crossover Cable

In crossover cable, TX and RX wires are cross connected. TX and RX wires are connected at opposite position on the end of cable.

Side A Side B
Green WhiteOrange White
GreenOrange
Orange WhiteGreen White
BlueBlue
Blue White Blue White
Orange Green
Brown White Brown White
Brown Brown
Crossover cable

Crossover cable is used to connects

  • Two computers
  • Two hubs
  • A hub to a switch
  • A cable modem to a router
  • Two router interfaces
Use of crossover cable

Console interface

All interfaces except console, are by default administratively down on router and switch. You have to connect with device (router or switch) via console interface, form where you can configure other interfaces and make them active to accept connection. Rollover ( also known as Console ) cable is used to connect console interface with PC. In rollover cable all wires have opposite position on each end.

Rollover cable

RJ-45

RJ-45 (Registered Jack) is a connector used to make straight-through, crossover, rollover cables.

RJ-45 Connector

While connecting cable in RJ-45 connector keep the clip in opposite direction.

Summary

Device ADevice BInterfaceCable
Router RouterSerialSerial Cable
Router RouterEthernetCrossover Cable
Router SwitchEthernetStraight-through Cable
Switch SwitchEthernetCrossover Cable
Switch Hub EthernetCrossover Cable
Switch PC EthernetStraight-through Cable
HubPC EthernetStraight-through Cable
Router PC ConsoleRollover Cable
Switch PC ConsoleRollover cable
Modem Router EthernetCrossover cable

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