If you want to have your own Tcl functions available when you start tclsh, you could use the scripting tcl init file configuration command that I've briefly mentioned in one of the previous posts. This command specifies a source file that is executed every time you start Tcl shell. The source file can contain function definitions, package declarations or any other Tcl code.

If you need to, you can specify multiple initialization files.

In a previous post I've described how you can use neighbor local-as feature to fix AS-number mismatch between adjacent autonomous systems. However, without additional options, the local-as is inserted in the AS-path of incoming BGP updates before any inbound filters. Your inbound filters thus have to match the local-as as well.

Marcus Jensen asked me a very interesting question:

I want to send 3 lines of configuration to a remote router, but I know the first line will kill my connection. Can I save these 3 lines of code to a text file, and then issue a Tcl command to add those to the running config?

The solution is much simpler and does not have to involve Tcl at all. The copy something system:running-config command merges the configuration commands in the source file with the current running configuration.

If you're running NTP and SNTP on the same router, SNTP will never synchronize with a configured SNTP server, as the NTP process captures the reply packet before SNTP has the chance to react.

SNTP multicast/broadcast client mode works in combination with NTP

NTP process could be running even if your running configuration has no NTP-related commands. It starts automatically whenever you enter NTP-related configuration (ntp logging configuration command is enough) and is not stopped when the last NTP-related configuration command is removed. You have to reload the router to kill it.

In a previous post, I've described how you can detect high CPU load with the Embedded Resource Manager (ERM). If you want to respond to these events, you could use the syslog event detector within EEM, but it's more reliable to use the new event resource detector available in EEM version 2.2 (introduced in IOS release 12.4(2)T). The resource detector is best used in Tcl policy; if you use it in EEM applet, the same applet is triggered every time a resource policy threshold (minor/major/critical, rising or falling) is crossed. Within the EEM applet it's almost impossible to detect which threshold was crossed.

Mike Nipp has wondered which syslog message to use to reliably detect router reload under all circumstances:

The problem I had with the SYS-5-RESTART message is I don't think you will get one if the power is suddenly pulled from the router. It does do a SNMP-5-COLDSTART and SYS-6-BOOTTIME on boot up.

I did an actual power-cycle test of a router and the SYS-5-RESTART message is reliably generated at every startup, be it from the power cycle or the reload command (I was not able to provoke an on-demand crash ;).

Cisco documentation has always claimed there were four well-known communities (the Internet community being one of them), while the RFC 1997 lists three well-known values. Unfortunately, many people blindly copy the IOS documentation without asking themselves “what the heck is the Internet community”.

David Winter wanted to detect high-CPU spikes and act on them. The first part (high CPU utilization) could be done with SNMP, but since IOS release 12.3(14)T, the right tool for the job is the Embedded Resource Manager (ERM).

The ERM syntax is a bit baroque (and not well documented), so let's work through the example: this is the configuration you need to detect high overall CPU utilization on the main CPU in the box:

I’m probably getting old … I keep forgetting the exact names (and capitalization) of route-maps I’ve configured on the router. The show route-maps command is way too verbose when I’m simply looking for the exact name of the route-map I want to use, so I wrote a Tcl script that displays the names of the route-maps configured on the router. If you add the -d switch, it also displays their descriptions (specifically, the first description configured in the route-map).

cpmf14 has left an interesting comment documenting how to perform a periodic back up of a file in router's flash to an FTP server:

event manager applet backup-crl
 event timer watchdog time 86400 maxrun 4294967295
 action 1.0 cli command "enable"
 action 2.0 cli command "copy flash:/iosca.crl ftp://username:[email protected]/" pattern "a.b.c.d"
 action 3.0 cli command "a.b.c.d" pattern "iosca.crl"
 action 4.0 cli command "iosca.crl"
 action 5.0 syslog msg "FTP backup successful"