Thursday, January 31, 2008

Cisco Router as DHCP Server

All Cisco Layer3 switches & routers, have the capability to run a DHCP server. Sooner or latter you will find yourself with the need to configure a router as a DHCP Server.

The configuration is quiet straight forward. Lets say we have the following interface to our LAN:
interface FastEthernet 0/0
 description Uplink to Users Segment
 ip address

Monday, January 14, 2008

Cisco's Core Dumps to an FTP

There are times when you will need to capture a core dump of a Cisco device that has been crashing.

Core dumps contains a copy of the router's entire memory contents. In some circumstances this will help technical support to determine what is causing the crash of your network device or will help the developers to pin-point bugs.

Cisco provides a simple way for doing this. In our case we are going to configure and FTP server as the destination for the core dumps.

My Cisco Virtual Lab Topology I

I have real Cisco routers and switches but most of the time I rather use virtual devices based on Dynamips. They are portable with my laptop, don't consume additional electricity and provide me with and environment to test features anywhere I go with my laptop. I use it to test QoS, MPLS, IP routing (with OSPF, EIGRP, BGP), gatekeepers configurations, load-balancing, etc. It is just as having the real thing with you.

For example, during my last trip I found myself running 15 routers on my laptop, doing a BGP load balancing configuration validation for a service provider. (Well, I managed to do the job but my laptop's battery was totally drained in little bit more than an hour). But the idea is that, it is a really flexible solution. (BTW, I run Linux so I don't have the memory limitations that the Windows instances have.)