Tag Archives: ios

10 Useful Cisco IOS Commands – Part 1

This is not a complete list of all the commands found in the Cisco IOS, instead I intend this page to be a simple reference of the commands I frequently come across when working with Cisco products.

Although, I tried to write a description for most of the commands found below some of them are self explanatory.

Schedule Router to Reload in X amount of minutes:

You can schedule a Cisco device to reload at a predetermined amount of time. The example below will reload a router in 25 minutes.

Router# reload in 25

System configuration has been modified. Save? [yes/no]: yes
Building configuration...
[OK]
Reload scheduled in 25 minutes by console
Reload reason: Reload Command
Proceed with reload? [confirm]

To cancel the reload just issue:

Router# reload cancel

Router#

***
*** --- SHUTDOWN ABORTED ---
***

Display CPU load:

Router# show proc cpu

CPU utilization for five seconds: 0%/0%; one minute: 0%; five minutes: 0%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
   1           0         2          0  0.00%  0.00%  0.00%   0 Chunk Manager
   2           4       192         20  0.00%  0.00%  0.00%   0 Load Meter
   3           0         1          0  0.00%  0.00%  0.00%   0 chkpt message ha
   4           0         1          0  0.00%  0.00%  0.00%   0 EDDRI_MAIN

Display available memory:

Router# show proc mem

Processor Pool Total:  162187652 Used:   20502480 Free:  141685172
      I/O Pool Total:   16777216 Used:    2831648 Free:   13945568
Transient Pool Total:   16777216 Used:      16584 Free:   16760632

 PID TTY  Allocated      Freed    Holding    Getbufs    Retbufs Process
   0   0   28163076    6754612   19372876        351         84 *Init*
   0   0      12052      79384      12052          0          0 *Sched*

Clear interface configuration:

Clear a specific interface of all configuration and return to a default state.

Router(config)# default interface fastEthernet 0/0

Building configuration...

Interface FastEthernet0/0 set to default configuration

Change hostname:

Router(config)# hostname R12BNY

Disable host to IP translation:

While harmless frequent “Translating…. domain server (255.255.255.255)” messages can result in waste of valuable time. The logical solution is to disable Host to IP Address Translation. After disabling the message will no longer appear.

Router(config)# no ip domain-lookup

Test network throughput with TTCP:

TTCP is hidden IOS command designed to measure network throughput. In order to use TTCP you need to configure a sender and a receiver. Keep in mind this will result in increased Router load.

R2# ttcp transmit 192.168.1.1

ttcp-t: buflen=8192, nbuf=2048, align=16384/0, port=5001  tcp  -> 192.168.1.1
ttcp-t: connect (mss 1460, sndwnd 4128, rcvwnd 4128)
ttcp-t: 16777216 bytes in 75696 ms (75.696 real seconds) (~215 kB/s) +++
ttcp-t: 2048 I/O calls
ttcp-t: 0 sleeps (0 ms total) (0 ms average)
R1# ttcp receive

ttcp-r: buflen=8192, align=16384/0, port=5001
rcvwndsize=0, delayedack=yes  tcp
ttcp-r: accept from 192.168.1.2 (mss 1460, sndwnd 4128, rcvwnd 2668)
ttcp-r: 16777216 bytes in 75696 ms (75.696 real seconds) (~215 kB/s) +++
ttcp-r: 8330 I/O calls
ttcp-r: 0 sleeps (0 ms total) (0 ms average)

Banner MOTD:

Change the message with which users will be greeted when logging in.

Router(config)# banner motd #

Enter TEXT message.  End with the character '#'.
You are entering the vicinity of an area adjacent to a location. The kind of place where there might be a monster,
or some kind of weird mirror. These are just examples; it could also be something much better.
Prepare to enter: The Scary Door.
#

Display IOS version:

Router# show version

Cisco IOS Software, 7200 Software (C7200-JK9S-M), Version 12.4(13b), RELEASE SOFTWARE (fc3)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2007 by Cisco Systems, Inc.
Compiled Wed 25-Apr-07 03:18 by prod_rel_team

ROM: ROMMON Emulation Microcode
BOOTLDR: 7200 Software (C7200-JK9S-M), Version 12.4(13b), RELEASE SOFTWARE (fc3)

Disable Cisco Discovery Protocol (CDP):

CDP allows a Cisco device to see an adjacent Cisco device along with the protocols and IP addresses it uses. While useful CDP is considered by some to be a risk because it provides information to potential attackers.

Router(config)# no cdp run

Back Up And Install The Cisco IOS Image

In order to back up the IOS you need a TFTP server, SolarWinds offers a Free TFTP Server.

If you have no idea what version of the IOS you are using use the show flash command.

Router#show flash
System flash directory:
File Length Name/status
1 3289170 d1206.bin
[3289236 bytes used, 905068 available, 4194304 total]
4096K bytes of processor board System flash (Read/Write)

Backup

From the console in privileged EXEC mode enter the copy flash tftp command. When requested enter the IP address of the TFTP server.

Router#copy flash tftp
Source filename []? d1205.bin
Address or name of remote host []? 192.168.1.21
Destination filename [d1205.bin]? y
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
3289170 bytes copied in 47.668 secs (69982 bytes/sec)

Restore

To copy the IOS from a TFTP server use the copy tftp command. When requested enter the IP address of the TFTP server containing the IOS.

Router#copy tftp flash
Address or name of remote host []? 192.168.1.21
Source filename []? d1206.bin
Destination filename [d1206.bin]?
Accessing tftp://192.168.1.21/d1206.bin...
Erase flash: before copying? [confirm]
Erasing the flash filesystem will remove all files! Continue? [confirm]
Erasing device... eeeeeeeeeeeeeeee ...erased
Erase of flash: complete
Loading d1206.bin from 192.168.1.21 (via Ethernet0): !!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
[OK - 3289170/6578176 bytes]
Verifying checksum... OK (0xB6BD)
3289170 bytes copied in 89.272 secs (36956 bytes/sec)

Password Recovery For The Cisco IOS

Connect a PC with a terminal emulation software to the console port on the Cisco router. Cisco 2620 router, IOS 12.2.

Settings for the terminal

9600 baud rate
No parity
8 data bits
1 stop bit
No flow control

Turn off the router, then back on.

After the router is on press the BREAK key(Alt + b on Tera Term) within 60 seconds of start to have the router in ROMMON.

The prompt will show.

rommon 1>

Then type confreg 0x2142 to boot from flash (this will bypass startup configuration).

rommon 1>confreg 0×2142

Type reset at the prompt (ignores saved configuration, then reboots).

rommon 2>reset

Press Ctrl-c to skip the initial procedure.

Type enable at the prompt.

Router>enable

Then the prompt changes to Router#.

Now type.

Router#configure memory

or

Router#copy startup-config running-config

commands will copy NVRAM in to memory.

To show the current configuration on the router use.

Router#show running-config

The output will be :
enable passwords
enable secret
vty
console password

which will be in encrypted or unencrypted format, encrypted passwords should be change to a new one.

To change encrypted or enable secret password do the following.

Router#
Router#configure terminal
Router(config)#enable secret 
Router(config)#exit

Issue the no shutdown command on every interface.

Router#
Router(config)#interface serial 0/1
Router(config-t)#no shutdown
Router(config-t)#exit

Type config-register use the value 0×2102.

Router(config)#config-register 0×2102

Press Ctrl-z to leave configuration mode.

Router#

Type write memory or copy running-config startup-config to commit all of the new changes and configurations.