Introduction to Cisco Router

Introduction to the Cisco IOS 

The Cisco IOS (Internetwork Operating System) is a command-line interface used by nearly all current Cisco routers and Catalyst switches. The IOS provides the mechanism to configure all Layer 2 and Layer 3 functions on Cisco devices.  

The IOS is structured into several modes, which contain sets of commands specific to the function of that mode. Access to a specific mode (and specific commands) is governed by privilege levels. (Both modes and privilege levels are covered in great detail in this guide).  

The following is a representation of the IOS command-line interface, with an example command: 

Router# show startup-config

All commands throughout all guides on this site will be represented like the above. The following is an explanation of each component of the above command: 

1.IOS Version Numbers

The latest version of the IOS (as of this writing) is 12.4(11)T. To view the
IOS version of your Cisco device: 

Router# show version 

The Cisco IOS is stored in Flash on Cisco routers and Catalyst switches, in a .BIN file format. It can be upgraded using one of several methods: 

a) Replacing the existing Flash stick

b) Via a TFTP server
c) Via Xmodem
d) Via a PCMCIA slot (not supported by all Cisco devices) 

The IOS .bin file stored in flash follows a specific naming convention. Observe the following IOS image: 

                                    c2600-ik9s-mz.121-3.T.bin 

The following is an explanation of each component of the above file name:

The IOS supports a wide variety of feature sets. The following is a list of common feature sets (and is by no means comprehensive):  

a) is

b) ipbase
c) ipvoice
d) advsecurityk9
e) advipservicesk9
f) ik9s
g) jk9s
h) io3
i) bin 

2.IOS Modes on Cisco Devices 
As stated earlier, the Cisco IOS is comprised of several modes, each of which contains a set of commands specific to the function of that mode.

  

a) By default, the first mode we enter when logging into a Cisco device is User EXEC mode. User mode appends a “>” after the device hostname:
Router> 

No configuration can be changed or viewed from User mode. Only basic status information can be viewed from this mode. 

b) Privileged EXEC mode allows all configuration files, settings, and status information to be viewed. Privileged mode appends a “#” after the device hostname: 
Router#

To enter Privileged mode, type enable from User mode:
Router> enable
Router# 

To return back to User mode from Privileged mode, type disable:
Router# disable
Router> 

c) Very little configuration can be changed directly from Privileged mode. Instead, to actually configure the Cisco device, one must enter Global Configuration mode: 
Router(config)#

To enter Global Configuration mode, type configure terminal from Privileged Mode: 
Router# configure terminal
Router(config)# 

To return back to Privileged mode, type exit:
Router(config)# exit
Router# 

As its name implies, Global Configuration mode allows parameters that globally affect the device to be changed. Additionally, Global Configuration mode is sectioned into several sub-modes dedicated for specific functions. Among the most common sub-modes are the following: 

a) Interface Configuration mode - Router(config-if)#
b) Line Configuration mode - Router(config-line)#
c) Router Configuration mode - Router(config-router)# 

Interface Configuration mode - To configure an interface, one must specify both the type of interface, and the interface number (which always begins at “0”). Thus, to configure the first Ethernet interface on a router: 

Router(config)# interface ethernet 0
Router(config-if)# 

Line Configuration mode - Lines identify ports that allow us to connect into, and then configure, Cisco devices. Examples would include console ports, auxiliary ports, and VTY (or telnet) ports. 

Just like interfaces, to configure a line, one must specify both the type of line, and the line number (again, always begins at “0”). Thus, to configure the first console line on a router: 
Router(config)# line console 0
Router(config-line)# 

Multiple telnet lines can be configured simultaneously. To configure the first five telnet (or VTY) lines on a router: 
Router(config)# line vty 0 4
Router(config-line)# 

Remember that the numbering for both interfaces and lines begins with “0.”

Router Configuration mode - Router Configuration mode is used to configure dynamic routing protocols, such as RIP.  

2.IOS Command Shortcuts 

Shortcuts are allowed on the IOS command-line, as long as the truncated command is not ambiguous. For example, observe the following commands: 

Router# clear
Router# clock
Router# configure
Router# connect
Router# copy
Router# debug 

We could use de as a shortcut for the debug command, as no other command here begins with de. We could not, however, use co as a shortcut, as three commands begin with those letters. The following error would be displayed: 
Router# co
% Ambiguous command: “co” 

If we type a command incorrectly, the IOS will point out your error:
Router# clcok
                  ^
% Invalid input detected at “^” marker 

  

3.Keyboard Shortcuts

Several hotkeys exist to simplify using the IOS interface: 

     Keyboard Shortcut                                                    Result 

CTRL-B (or Left-Arrow)                            Moves cursor back one character

CTRL-F (or Right-Arrow)                          Moves cursor forward one character

CTRL-A                                                      Moves cursor to beginning of a line.

CTRL-E                                                      Moves cursor to end of a line

ESC-B                                                         Moves cursor back one word

ESC-F                                                         Moves cursor forward one word

CTRL-P (or Up-Arrow)                              Returns previous command(s) from history                                                                                buffer

CTRL-N (or Down-Arrow)                        Returns next command from history buffer

CTRL-Z                                                      Exits out of the current mode

TAB                                                            Finishes an incomplete command (assuming it is

                                                                    not ambiguous)

4.Terminal History Buffer  

The Cisco IOS keeps a history of previously entered commands. By default, this history buffer stores the previous 10 commands entered. To view the terminal history buffer:  

RouterA# show history 

enable
config t
hostname RouterA
exit
show history

 

The Up-Arrow key (or CTRL-P) allows you to scroll through previously entered commands. To scroll back down the list, use the Down-Arrow key (or CTRL-N).  

To adjust the number of commands the history buffer stores (range 0-256): 

RouterA# terminal history size 30

 

5.Enable Passwords  

The enable password protects a router’s Privileged mode. This password can be set or changed from Global Configuration mode:  

Router(config)# enable password MYPASSWORD
Router(config)# enable secret MYPASSWORD2 

The enable password command sets an unencrypted password intended for legacy systems that do not support encryption. It is no longer widely used. 

The enable secret command sets an MD5-hashed password, and thus is far more secure. The enable password and enable secret passwords cannot be identical. The router will not accept identical passwords for these two commands. 

6.Line Passwords and Configuration
Passwords can additionally be configured on router lines, such as telnet (vty), console, and auxiliary ports. To change the password for a console port and all telnet ports:

Router(config)# line console 0
Router(config-line)# login
Router(config-line)# password cisco1234

Router(config)# line vty 0 4
Router(config-line)# login
Router(config-line)# password cisco1234

Router(config-line)# exec-timeout 0 0
Router(config-line)# logging synchronous

Router(config-line)# exec-timeout 0 0
Router(config-line)# logging synchronous

The exec-timeout 0 0 command is optional, and disables the automatic timeout of your connection. The two zeroes represent the timeout value in minutes and seconds, respectively. Thus, to set a timeout for 2 minutes and 30 seconds: 

Router(config-line)# exec-timeout 2 30

The logging synchronous command is also optional, and prevents system messages from interrupting your command prompt. 

By default, line passwords are stored in clear-text in configuration files. To ensure these passwords are encrypted in all configuration files: 

Router(config)# service password–encryption 

7.Router Interfaces

To configure an interface, one must specify both the type of interface, and the interface number (which always begins at “0”). Thus, to configure the first Ethernet interface on a router:  

Router(config)# interface ethernet 0
Router(config-if)#  

Certain router families (such as the 3600 series) are modular, and have multiple “slots” for interfaces. All commands must reflect both the module number and the interface number, formatted as: module/interface 

Thus, to configure the third Fast Ethernet interface off of the first module:
Router(config)# interface fastethernet 0/2
Router(config-if)#

By default, all router interfaces are administratively shutdown. To take an interface out of an administratively shutdown state:
Router(config)# interface fa 0/0
Router(config-if)# no shutdown  

Notice the use of fa as a shortcut for fastethernet in the above example. To manually force an interface into a shutdown state:
Router(config-if)# shutdown  

  

To assign an IP address to an interface:
Router(config-if)# ip address 192.168.1.1 255.255.255.0

An additional secondary IP Address can be assigned to an interface:
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Router(config-if)# ip address 192.168.1.2 255.255.255.0 secondary 

Serial interfaces require special consideration. The DCE (Data Communication Equipment) side of a serial connection must set the speed, or clock rate, for the DTE (Data Terminal Equipment) side. Clock rate is measured in BPS (bits-per-second).

To set the clock rate, if you are the DCE side of a serial connection:
Router(config)# interface serial 0
Router(config-if)# clock rate 64000 

Note:- The clock rate serves to synchronize the receiver on the other side of the link. Each clock pulse signals the transmission of a bit. Note that it is mainly used in lab setups.

 

When we set the clock rate for a serial interface, we are setting the speed of the interface, in other words, the bandwidth (bandwidth meaning rate of data transfer). When using this command it's in the form of bits: 64000 bits = 64 kb.

8. Managing Configuration Files

Cisco IOS devices employ two distinct configuration files

• running-config – stored in RAM, contains the active configuration
  
• startup-config – stored in NVRAM (or flash), contains the saved
  configuration
  

Any configuration change made to an IOS device is made to the runningconfig. Because the running-config file is stored in RAM, the contents of this file will be lost during a power-cycle. Thus, we must save the contents of the running-config to the startup-config file. We accomplish this by using the copy command from Privileged mode:

Router# copy running-config startup-config

The copy command follows a very specific logic: copy [from] [to]. Thus, if we wanted to copy the contents of the startup-config file to running-config:

Router# copy startup-config running-config

We can use shortcuts to simplify the above commands:

Router# copy run start

Router# copy start run

To view the contents of the running-config and startup-config files:

Router# show run

Router# show start

To delete the contents of the startup-config file:

Router# erase start

If the router is power-cycled after erasing the startup-config file, the router will enter Initial Configuration Mode (sometimes called Setup Mode). This mode is a series of interactive questions intended for quick reconfiguration of the router.

Initial Configuration Mode can be exited by typing CTRL-C.

9.Some useful commands

-Piping Commands 

In newer versions of the Cisco IOS, the output of show commands can be filtered to remove irrelevant lines, through the use of the pipe “ | ” character. The following command will display the contents of the startup-config, beginning with the first line containing the text ethernet:

Router# show startup | begin ethernet 

The following command will exclude all lines containing the text ethernet:
Router# show startup | exclude ethernet

The following command will include all lines containing the text ethernet:
Router# show startup | include ethernet

To change the hostname of your router:
Router(config)# hostname MyRouter
MyRouter(config)# hostname MyRouter

To assign a description to an interface for documentation purposes:
Router(config)# interface serial 0
Router(config-if)# description SBC T1 connection to India
Router# show interfaces

To create a banner message which users will see when logging into an IOS
device:
Router(config)# banner motd # 

The # symbol is used as a delimiter to indicate the beginning and end of the banner. Any character can be used as a delimiter.

-The Configuration Register 

The configuration register (config-register) is a hexadecimal value that controls various aspects of how a router boots, including:

a) Baud Rate
b) Boot Messages (enable/disable)
c) Break (disable/ignore)
d) Flash (read-only, read-write)

e) NVRAM (use startup-config/bypass startup-config) 

The default config-register is 0x2102. To view your router’s current config-register setting:
Router# show version  

Common config-register settings include: 

Remember, 0x2102 is the default config-register value on Cisco routers. In order to upgrade the Cisco IOS, the config-register must be changed to 0x2101, so that the Flash memory becomes writeable.  

To change the config-register from the IOS:
Router(config)# config-register 0x2142
This configuration change does not take affect until the next reboot. 

10.Backing up and Restoring the Cisco IOS

The Cisco IOS is stored in flash. Multiple IOS files can be loaded into flash, assuming there is enough free space. WE can view available free space, and the name of any file(s) in flash, by typing  

Router# show flash  

To backup the IOS, a TFTP server is required. The TFTP server must have IP connectivity to the router.
To backup the IOS file from the router’s flash to the TFTP server:
Router# copy flash tftp  

We will be prompted for the following information:

a) Address of remote host (the TFTP server)
b) Source file name (the name of the file in flash)
c) Destination file name

To load an IOS file from a TFTP server to the router’s flash:
Router# copy tftp flash

The process is nearly identical to copy a startup-configuration file to or from a router’s NVRAM:
Router# copy startup tftp
Router# copy tftp startup

11.CDP (Cisco Discovery Protocol) 

CDP is a Cisco propriety protocol used to collect information about locally attached Cisco switches and routers. CDP is enabled by default on all IOS enabled routers and switches, and sends out updates every 60 seconds.

CDP will provide the following information about directly connected neighbors: 

a) Device ID – hostname of remote router/switch
b) Local Interface – interface that remote router/switch is directly connected to
c) Holdtime – amount of time before remote device information is purged from CDP table
d) Capability – Type of remote device (router, switch, host)
e) Platform – Model of remote device 

To view CDP timers and hold-down information:
Router# show cdp

To display neighbor information:
Router# show cdp neighbors

To display traffic statistics:
Router# sh cdp traffic

To display port and interface information:
Router# sh cdp interface

To disable CDP on an interface:
Router(config-if)# no cdp enable

To globally disable CDP:
Router(config)# no cdp run 

12.Telnet
It is possible to telnet from a router into a remote device, using either the hostname or IP address of the remote device:
Router# telnet Router2
Router# telnet 172.17.1.2

To exit a telnet session:
Router2# exit

To return to the router we telnetted from, without exiting the session:

a) Hold CTRL+SHIFT+6 and then release

b) Type the character x
To view all open telnet sessions:
Router# show sessions 

13.Privilege Levels
IOS devices have a total of 16 privilege levels, numbered 0 through 15. User Exec mode is privilege level 1. Privileged Exec mode is privilege level 15. 

We can create a custom Privilege level, including the commands users are allowed to input at that mode:
Router(config)# privilege exec all level 3 show interface
Router(config)# privilege exec all level 3 show ip route
Router(config)# privilege exec all level 3 show reload 

To then enter that privilege level from User Mode:
Router> enable 3 

14.Observing Performance Statistics on Cisco Routers
To view the processor load on a Cisco Router:
Router# show processes cpu

15.IOS Troubleshooting Commands

The show tech-support command prints to screen every configuration file, and the output of several important show commands. This can be redirected to a file and either viewed or sent to Cisco for troubleshooting purposes:
Router# show tech-support 

The debug command is a powerful tool to view real-time information and events occurring on an IOS device. As with the show command, there are a multitude of arguments for the debug command. An example debug command is as follows:
Router# debug ip rip events

To disable a specific debugging command, simply preprend the word no in front of the command:
Router# no debug ip rip events

To enable all possible debugging options on an IOS device:
Router# debug all

Using the debug all command is not recommended, as it will critically impair router performance.  

To disable all possible debugging options on an IOS device:
Router# no debug all 

  

  

  

  

   

  

  

Introduction to Router

1.Router

Router is a internetworking device which connect the multiple device with geographical.

Router is a device which provides communication between two or more network. Router finds the the best path (route).

2.Function of Router

1. Internetwork router

2. Best Path selection

3. Packet switching

4. Packet forwarding

3.Router Interface

1. Ethernet:- It is a LAN interface some of the  router's have RJ45 port for 10Base-T and some have other 15 pins female port which is called (Attachment unit interface)

2. AUI - Attachment unit interface

    It is a 15 Pin female interface to connect the LAN. Transceiver is used for connecting AUI port to LAN, Hub/Switch.

3. Serial Port

IT is a 60 pin female interface for leased line connection. Serial port is used for WAN connectivity. Smart serial port is 26 pins V.35 cable used to connect between leased line modem of serial router.

4. BRI/PRI -  Basic Rate interface

   It is RJ45 WAN interface for ISDN line. It is known as remote administrative port.

   This is used for remote administrative/configuration. In it console/rollover cable is used.

5. Console Port- It is a RJ45 port used to configure router for first time. It is  known as local administrative port. This port is used for initial configuration, password recovery and advanced trouble shooting. It is most important port for router.

6. Auxiallary Port- It is RJ45 port which is used to connect or used for remote access administrator It is known as remote administrative port. In this Rollover and Console cable is used..

7. Asyn Port - 

4.Cisco Hierarchical Model

There are three layer in cisco hierarchical model 

(i) Access layer 

(ii) Distribution layer

(iii) Core layer

Access layer - Router which are used at branch office known as access layer or [ROBO] Remote office branch office. Access layer series [700_ _ _ _ _2500]

Distribution layer - Routers which are used at head office are known as distribution layer/Enterprises layer.

Distribution layer [2600_ _ _ _ _ _ _5000]

Core layer - Router which are used by internet service provide are known as core on backbone routers.

Core layer series [7000_ _ _ _ _ _12000 or above] 

5.Router Categories

Modular Router - These type of routers have upgradable slots and the number of ports can be increased just by adding cards in the slots. 

Modular Router Series 2600 - 12000 or Above

Non Modular Router - These types of routers have fixed numbers of ports.

Non Modular Router Series 700-2500

6.Router Memory Element

1. Boot ROM -  It stores the MINI IOS [Internetworking Operating System] image with limited capabilites and post routines and core level OS for maintenance.

A boot strap programe's  is located here. It is same as BIOS [Basic Input Output System] of PC.

2. Flash - It is an erasable programmable ROM chip, that holds most the [IOS] image. It maintains everything when router is turned off.

Note:- IOS is stored here. IOS is command line interface.

3. Non-volatile memory - It is a rewritable memory that holds router configuration files NVRAM retains the information whenever router is reboot once configuration is saved.

Note:- Router configuration saved in NVRAM and this saved configuration is called as 'startup configuration'. NVRAM similar to hard disk. It is also known as permanent storage.

4. RAM (Random Access Memory) - RAM holds IOS running IOS configuration RAM is a volatile memory and looses its information when the router is turned off. The configuration present in RAM is called running configuration. It is also known as temporary storage.

IOS Version

7.Working mode of Cisco Router

1.  User Mode [Default mode] - User mode is the first default mode. It means that whenever router boots successfully. It land into the user mode.

Note:- Router cannot be configured from this mode. It is only for monitoring purpose.

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

2. Privileged mode - It is the administrative mode. We can check whether setting and configuration which have implemented on router.

Privileged mode  allow the users to view the system configuration, restart the system and enter the router configuration mode. Privileged mode also allows all the commands that are the available in the user mode. Privileged mode can be identified by the Router#  From the usermode, a user can change to privileged mode by enter the >Enable command.

3. Global configuration mode - From this mode we can configure router interface and settings, implements security level, authentication, password, Telnet etc.

Global configuration mode allows the user to modify the running system configuration. From the privileged mode a user can move to configuration mode by running the command #configure terminal 

Global configuration mode can be identified by Router(config)# 

4. ROMMAN (ROM Mon) MODE - If our router or access server does not find a valid system image to load, the system will read only memory (ROM) monitor mode. ROM Monitor (ROMMON) mode can also be accessed by interrupting the boot sequence during startup.

ROMMON (ROM Monitor) Mode can be identified by  the ROMMON1>

5. Line configuration mode:-

6. Router mode :-

7. Subinterface mode:-

8.Routing

It is a process which transfer the data one router to another router.

-Types of Routing

1.  Static Routing

2.  Dynamic Routing

3.  Default Routing

Static Routing - This static routing entry is created manually by the network administrator in the routing table of a router. All the routers path is predetermined in the network by the network designer which entered line by line in the routing table of each other. Once all the router in the internetwork have been programmed with the static routes they do not need to try to automatically discover new routes.

We can configure  route by manually into routing table. Static routing is used in small network, not in large network.

Dynamic Routing - Dynamic routing is configured on network where the router can learn the changes in the network topology automatically without on administrator intervention in configuring routes on the router. 

We can configure route by protocol. Like RIP, IGRP, EIGRP, OSPF, BGP, IS-IS. Dynamic routing is used in large network.

Default Routing - Default routing is defined as the route that is not present in the network. Default routing is possible with the routers that have only one exit path from network.

9.Routing Table 

A routing table contains series of entries called routes that the information about location of different network ID in the internetwork.

It is a database which stores the information of about the network or network path.

Use #show ip route command to check the route.

Loops-

Split Horizon - It is a method of preventing a routing loop in a network. The basic principal is simple information about the routing for a particular packet is never sent back in the direction from which it was received.

Routing Loops - A routing loop is a serious network problem which happens when a data packet is continuously routed through the same routers over and over. The data packets continue to be routed within the network in an endless circle.

Types of Protocol

1. Routing Protocol :- Routing protocols are the set of guideliness that determine the appropriate path the packet should take to forward data.

The routing protocol play a major role  by automatically updating the table whenever the change the network.

These protocol are those protocol which defines the best route for the data transmission and update routing table. Like:- RIP, IGRP, EIGRP OSPF and IS-IS.

2. Routed Protocol :- These protocols are those protocol which define the routing and addressing.

Like : - IP, IPX and Apple Talk

Types of Routing Protocol

1. Interior Routing Protocol :- These are the protocol that designed for the use of  inside single AS.

Like:- RIP, IGRP, EIGRP OSPF and IS-IS.

2. Exterior Routing Protocol :- These are the protocol that designed for the use of between and different AS. Like :- BGP

Types of Interior Routing Protocol

1. Distance Vector Protocol - Where the router communicate with each other and update the network information in the routing table. RIP and IGRP are the example of distance vector routing protocol. These protocol update neighbour's routing table after a particular time.

a) RIP update timer 30 sec

b) IGRP update timer 90 sec

2. Link State Protocol :- In the link-state routing, the router which communicating share the status of  the links on the network. This includes a connection type , speed of the links and metric cost. This way protocol know the state or map of the entire network. The protocol send link state advertisement (LSA) that contain routing information and details of the router that send the information. LSA are generated when there are some changes in the network. Eg:- OSPF and IS-IS

3. Hybrid Protocol :- It is the combination of Distance Vector Routing Protocol and Link State Routing Protocol. It can look at bandwidth, load, delay, reliability and hop count to make a decision on what is the best route. Eg:- EIGRP

Serial Port and Cable

Serial ports like USB and RS-232 are for connecting peripheral devices directly to the computer. 

In computer networking, a serial port enables external modems to connect to a PC or network router via a serial cable. The term 'serial' signifies that data sent in one direction always travels over a single wire within the cable.

A serial cable is a cable that used to transfer information between two devices using a serial communication protocol. The form of connectors depends on the particular serial port used. A cable wired for connecting two DTEs directly is known as a null modem cable.

Fastethernet Port and Cable

DCE