Sometimes we have a need for debugging and Cisco has a lot of options for debugging, this is one of the things why I definately prefer Cisco to HP or other network vendors.
I did some vol2 labbing yesterday and had a need to debug OSPF packets to verify that an adjacency was being form over unicast and not multicast. Sounds easy but when running labs with many neighbors there can be a lot of packets flowing and we might miss some important information when debugging. If we are debugging IP packets we can specify an ACL to narrow down the selection but I am not aware of such an option when debugging routing protocols, at least not for the IGP’s. What I found out is that there is an option for settings conditions on what to debug. This is how we do it.
So we have some different options we can used, the two most obvious are ip and interface. I will show how to debug OSPF packets coming in or out a specific interface, this will narrow down traffic a lot if we have multiple neighbors.
Only traffic coming in or out Serial 0/1 will be debugged. Use show debug condition to see what conditions has been set.
Lets debug OSPF packets.
So this is a very handy command to use when the need for debugging arises. As every CCIE candidate we should avoid using Google to find this information and you can find the document describing this feature by going to Cisco.com -> Configure -> Products -> Cisco IOS and NX-OS Software -> Cisco IOS -> Cisco IOS Software Release 12.4 Family -> Cisco IOS Software Releases 12.4T -> Reference Guides -> Command References -> Debug
The direct URL is here.