Category: Command Line Interface

I've almost started writing a Tcl procedure to display top-10 CPU-intensive processes on a router ... and then discovered the sorted option of the show processes cpu command. Even more, starting in IOS release 12.2T, the show processes cpu history command gives you a nice CPU utilization graph.

The Warm Reload functionality introduced in IOS release 12.3(2)T significantly reduces the reload time. In my test lab, the reload time of a Cisco 2800 router booting from flash was reduced from 135 to 54 seconds as measured by the %SYS-6-BOOTTIME: Time taken to reboot after reload ... syslog message.

The theory behind warm reload is simple: the router saves initial data (as stored in IOS image) in a separate memory region and reuses saved data together with IOS code already residing in RAM to restart IOS. Of course, the IOS code (depending on platform's memory management capabilities) or saved data could get corrupted, therefore the warm reload cannot be used continuously (and the router falls back to traditional reload if the router crashes before a specified time interval).

Warm reload is configured with the warm-reboot count number uptime minutes configuration commands. After it has been configured, a router reload (or power-up) is needed to initialize the saved data region. When the warm reboot is operational (as verified with the show warm-reboot command), you can use reload warm command to start it.

In a previous post, I’ve described how to execute a Tcl file with the tclsh command.

You can do even more than that: you can pass parameters to the executed file. Every word you enter after the file name in the tclsh command line is passed as a parameter to the Tcl code you execute. To get these parameters in Tcl, use Tcl commands similar to the code below:

The more command display the specified file as a hex dump if the contents don't look like a text file. In my example, it didn't like the CR/LF pairs in the Autorun.inf file written on an USB token by a Windows PC, but you could also dump an IOS image or a tar archive used by SDM (or other web-based applications). To force the display format, use the /ascii, /binary or /ebcdic (for IBM/SNA gurus) parameters. Cool feature ... IOS is obviously full of hidden gems :)

router#more usbflash1:Autorun.inf
00000000:  5B617574 6F72756E 5D0D0A6F 70656E3D    [aut orun ]..o pen=
00000010:  496E7374 616C6C65 722E6578 650D0A69    Inst alle r.ex e..i
00000020:  636F6E3D 496E7374 616C6C65 722E6578    con= Inst alle r.ex
00000030:  650D0A41 6374696F 6E3D4C61 756E6368    e..A ctio n=La unch
00000040:  20496E73 74616C6C 65722066 6F722047     Ins tall er f or G
00000050:  6F6F676C 65204170 706C6963 6174696F    oogl e Ap plic atio
00000060:  6E73200D 0AXXXXXX XXXXXXXX XXXXXXXX    ns . .XXX XXXX XXXX

I've always wanted to be able to execute a show command while configuring a router (I'm never good at remembering subinterface numbers). A while ago Cisco introduced the do configuration command that allows you to execute any exec-level command (including telnetting to another device) without leaving the current configuration mode.

There are two ways you can configure local usernames without a password:

• By using the username user command without the password option, you create a username that has a blank password (the operator has to press ENTER at the Password: prompt)
• With the username user nopassword command, you create a user where the operator will not be prompted for the password at all.

Hopefully, you would use such usernames only with the autocommand option to give guest users a short overview of the router's operation (for example, display the interface status).

Note: this article is part of You've asked for it series.

Hard-core IOS oldtimers could probably remember the sequence of parameters in the extended IP ping dialog even when woken up in the middle of the night. However, another venerable tradition has been made obsolete in one of the IOS 12.x releases: the ping command now accepts parameters like data, repeat, size, timeout or source.

For example, to send 500 long pings with data pattern 0000 to 10.0.0.10, you could use the ping ip 10.0.0.10 data 0000 repeat 500 size 18000 validate command.

Starting in IOS release 12.3(2)T, Tcl shell is accessible from the command line interface with the tclsh command. After entering this command, you get the Router(tcl)# prompt and can enter individual Tcl commands (the help is confusing, though – you get help on exec-mode commands, but none of them work).

Cisco IOS long had the autocommand option by which you could attach any command to a username and have it execute after successful login. For example, username x autocommand show ip interface brief command would configure the router to display the interface status after someone would log in as user x.

After the autocommand is executed, the user is logged out and the session is disconnected, unless you configure the username user nohangup option, which causes the session to remain active, giving the operator another login prompt.

Displaying configuration of a single interface can be a time-consuming task if your router has extremely long configuration (for example, high-end device with hundreds of interfaces, route-maps, access-lists etc.). In this case, the interface keyword of the show running-config command becomes extremely useful.