CISCO IOS in a Nutshell

show Commands

As you work with IOS, you’ll become intimately familiar with the show commands. They are among the most useful commands you will ever use; they allow you to view just about any settings within the router. Issuing the command show ? produces output like this:

Router>show ?
  clock     Display the system clock
  history   Display the session command history
  hosts     IP domain-name, lookup style, nameservers, and host table
  sessions  Information about Telnet connections
  snmp      snmp statistics
  terminal  Display terminal configuration parameters
  users     Display information about terminal lines
  version   System hardware and software status

The show command has many different subcommands. However, notice that we are in user mode. In privileged mode, the show command has a lot more subcommands, which would take up a few pages if we listed them here. The important thing to remember is that show commands often have more than one keyword. For example, the command show ip route works by itself, but there are also many other options that can be applied to it. For example:

router#show ip route ?
  Hostname or A.B.C.D  Network to display information about or hostname
  bgp                  Border Gateway Protocol (BGP)
  connected            Connected
  egp                  Exterior Gateway Protocol (EGP)
  eigrp                Enhanced Interior Gateway Routing Protocol (EIGRP)
  igrp                 Interior Gateway Routing Protocol (IGRP)
  isis                 ISO IS-IS
  odr                  On Demand stub Routes
  ospf                 Open Shortest Path First (OSPF)
  rip                  Routing Information Protocol (RIP)
  static               Static routes
  summary              Summary of all routes
  supernets-only       Show supernet entries only
  <cr>

I certainly haven’t explained routing enough for you to understand the output of this command. However, you can see how to find show keywords with the question mark. The <cr> shown in the previous example indicates that you can hit Return at this point and the command will work. In other words, show ip route is a valid command. The other keywords are optional.

In each section of this book, I emphasize the appropriate show commands for the topic. For the topics covered in this chapter, the following show commands are extremely useful:

• show version

• show history

• show users

The show version command gives a lot more information than just the version of IOS that the router is currently running. You will see this command pop up a few more times later in this book. For now, you can see that it tells us the router type, the IOS image, the system uptime, the current IOS version, all the available interfaces, and the amount of memory on the router:

Router#show version
Cisco Internetwork Operating System Software 
IOS (tm) 2500 Software (C2500-AJS40-L), Version 11.3(5)T,  RELEASE SOFTWARE (fc1)
Copyright (c) 1986-1998 by cisco Systems, Inc.
Compiled Wed 12-Aug-98 05:53 by ccai
Image text-base: 0x0305770C, data-base: 0x00001000

ROM: System Bootstrap, Version 11.0(10c), SOFTWARE
BOOTFLASH: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c),
RELEASE SOFTWARE (fc1)

Router1 uptime is 1 week, 2 days, 8 hours, 48 minutes
System restarted by reload
System image file is "flash:c2500-ajs40-l_113-5_T.bin", booted via flash

cisco 2520 (68030) processor (revision M) with 6144K/2048K bytes of memory.
Processor board ID 10353279, with hardware revision 00000003
Bridging software.
X.25 software, Version 3.0.0.
SuperLAT software copyright 1990 by Meridian Technology Corp).
TN3270 Emulation software.
Basic Rate ISDN software, Version 1.1.
1 Ethernet/IEEE 802.3 interface(s)
2 Serial network interface(s)
2 Low-speed serial(sync/async) network interface(s)
1 ISDN Basic Rate interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read ONLY)

Configuration register is 0x2102

The show history command gives a log of the router commands you have used. The length of this history log depends on the size set by the terminal history command. The default is 10 lines.

Router#show history
  show history
  show terminal
  show users
  enable
  show version

The show users command gives a complete listing of all currently connected users:

Router#show users
    Line     User      Host(s)               Idle Location
   2 tty 2   steve1    idle
   5 tty 5   john2     Async interface          2