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Debugging on Cisco Nexus

I had an issue where I had a need to do some PIM debugging recently on the Nexus platform in an MPLS environment and there are some nice features that make it pretty handy to use.

First off I did what I usually do and forgot to specify the VRF I wanted to actually debug PIM in so received no log messages. I looked for a bit to see where I could specify the VRF but there wasn’t any option under the debug command:

n7k-dis2# debug ip pim ? assert PIM Assert packet events bidir PIM Bidir DF packet events data-register PIM data register packet events ha PIM system HA events hello PIM Hello packet events internal PIM system internal events join-prune PIM Join-Prune packet events mvpn MVPN related events null-register PIM Null Register packet events packet PIM header debugs policy PIM policy information rp PIM RP related events vpc VPC related events vrf PIM VRF creation/deletion events

That VRF option is not the one to specify the VRF, it debugs just what the description says it does.

Then I found you can specify debug-filters! Here is where you can specify which VRF to actually apply the debugging command to, along with alot of other filtering options:

n7k-dis2#debug-filter ip pim ? group Debug information for a particular Group interface Debug information for a particular Interface vrf Debug information for a particular VRF n7k-dis2# debug-filter ip pim vrf user

As you can see, you can filter your debugs to a specific multicast group and/or interface as well. Now that we have applied the debug filter to the user VRF, now we can turn on the specific PIM debugging we want to see:

n7k-dis2# debug ip pim join-prune 2013 Aug 13 13:04:18.022567 pim: [7034] (user-base) No (, route exists, not to us 2013 Aug 13 13:04:18.022615 pim: [7034] (user-base) No (, route exists, not to us 2013 Aug 13 13:04:18.022627 pim: [7034] (user-base) ----- 2013 Aug 13 13:04:18.084726 pim: [7034] (user-base) Received Join-Prune from on mti5, length: 34, MTU: 1376, ht: 420 2013 Aug 13 13:04:18.084758 pim: [7034] (user-base) Upstream address:, group count: 1, holdtime: 420 2013 Aug 13 13:04:18.084770 pim: [7034] (user-base) Group:, join-list count: 1, prune-list count: 0 .....

Now this produced a lot of output so you could have applied another debug-filter to filter on a specific address, packet direction, interface, etc. It is pretty easy to extract exactly what you want to see in the debug output.

You can also send the output of a debug to a file like so (I named the file “test”):

n7k-dis2# debug logfile test size ? 4096-4194304 Enter the logfile size in bytes

Categories: cisco, nexus
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