Category: Network Management

In a previous post, I've described how you could generate a (almost) continuous ping from a router using the extended ping command. While that approach is extremely simple to implement, it ties up a line (and if you're working from the console, it's highly impractical). You could get the same results (as Tom has already pointed out) using IP SLA feature of Cisco IOS. Configure the ping request with commands similar to these:

IOS release 12.2(13)T (integrated in IOS release 12.3) has added the capability to redirect output of an IOS show command to a file. This feature uses Unix-style pipes (similar to the include, exclude and section keywords) and adds append, redirect and tee (redirect + print) keywords.

The show output can be redirected to a local filename (in flash, on usb token or even in NVRAM) or sent to a remote server (currently only FTP and TFTP servers are supported). For example, the show ip interface brief | redirect ftp://student:[email protected]/ifstatus command will store the current interface status to an FTP server.

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.

One of my readers has asked an interesting question: can you reload a router when pinging a specific IP address from it fails? While there are other ways of dealing with stuck interfaces or routing processes, sometimes such a drastic measure is the only workaround, so here's how you do it:

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.

In certificate-based IPSec deployments, the router has to establish an approximately valid date and time before it can use a certificate to establish IPSec session (as most certificates were issued after March 1st 2002, which is the default initial value, they are not valid until the router has acquired an approximately correct date-and-time).

This requirement is not a problem for most router models, as they have battery-backed hardware clock that continues running even when a router is reloaded or powered down. The low-end models, though, have a problem, as they always start with the default date/time after the reload. These devices have to get their time from an NTP/SNTP server before being able to establish the IPSec session. If the (S)NTP server is only accessible across the VPN, you have a nice chicken-and-egg problem.

With IOS file system (IFS) introduced in IOS release 11.3AA (integrated in 12.0), IOS got the more command that displays any local or remote file that you could specify with IFS. The obvious use of the more command would be display of startup configuration (more nvram:startup-config), but you could also display built-in Tcl EEM policies (for example, more system:lib/tcl/http.tcl) or remote router configurations (for example, more tftp://host/cfg-file). But that's not all, you could even troubleshoot web servers and display HTML generated by the web server (for example, more http://192.168.0.2/index.html).

If you need interface counters on subinterfaces or virtual interfaces, you can emulate them with an empty policy-map, for example:

policy-map Count
 class class-default
!
interface Serial0/0/0.100 point-to-point
 service-policy input Count
 service-policy output Count

The IP Service Level Agreement (SLA) measurement feature of Cisco IOS is extremely SNMP-oriented. For example, there is no easy way to generate a logging message when an SLA operation fails (or exceeds the threshold). However, Embedded Event Manager reading SNMP variables can help you get there.