Viewing SPF Information

Viewing SPF Information
Frequent SPF calculations can indicate a problem in your network. Periodic SPF calculations
occur every 15 minutes. If you are encountering more frequent calculations than the periodic
calculations, you could have a problem in your network. You can view SPF calculations with
the command show isis spf-log:
Austin#show isis spf-log
Level 1 SPF log
When Duration Nodes Count Last trigger LSP Triggers
00:36:38 3124 40 1 Austin.00-00 TLVCODE
00:33:25 3216 41 5 Austin.00-00 TLVCODE NEWLSP
00:31:40 3096 41 1 Dallas.00-00 TLVCODE
00:29:01 3004 41 2 Austin.00-00 ATTACHFLAG LSPHEADER
Verifying and Troubleshooting IS-IS 231
00:29:46 3384 41 1 Austin.00-01 TLVCODE
00:28:01 2932 41 3 Austin.00-00 TLVCODE
00:27:30 3140 41 1 PERIODIC
00:24:30 3144 41 1 Austin.01-00 TLVCODE
00:21:45 2908 41 1 Austin.01-00 TLVCODE
00:20:57 3148 41 3 Plano.00-00 TLVCODE TLVCONTENT
00:17:46 3054 41 1 Austin.00-00 TLVCODE
00:14:35 2958 41 1 Houston.00-00 TLVCODE
00:12:30 3632 41 1 PERIODIC
00:10:31 2988 41 1 Austin.00-01 TLVCODE
00:09:44 3016 41 1 ElPaso.00-00 TLVCODE
00:06:02 2932 41 1 Plano.00-00 TLVCONTENT
00:04:29 2988 41 2 Plano.00-00 TLVCONTENT
00:02:58 3228 41 1 Austin.00-00 TLVCODE
00:01:29 3120 41 3 Waco.03-00 TLVCONTENT
This command informs you how long it was between SPF calculations, how long they took,
how many devices were involved, how many triggers caused the calculation, the last LSP that
caused the trigger, and what the triggers were. Note the timing of the periodic triggers—separated
by 15 minutes—down to the second. It really is like clockwork.
There are a number of debug commands that can be used to help you better understand what
is happening with the SPF calculations. The following is a list of some of the more common
debug commands with an explanation of each:
debug isis spf-events The debug isis spf-events command is best used when you want to
see the IS-IS routes that will be placed in the routing table. The command also informs you if a
route was rejected from being added to the routing table. This could occur if the route already
exists in the routing table with a lower administrative distance than IS-IS.
debug isis spf-triggers The debug isis spf-triggers command is best used when you need
to find out what is triggering a SPF calculation. The command informs you what level the SPF
calculation was done for and what the cause of the calculation was.
debug isis spf-statistics The debug isis spf-statistics command informs you how long
it took to perform an SPF calculation.
Before diving too deep into IS-IS troubleshooting, try the clear isis * command.
It clears up a number of adjacency issues (and others) caused by various
inconsistencies that are simply “ghosts in the machine.”
By now, you should have the proper tools at hand to configure, verify, and troubleshoot an
IS-IS network. My suggestion would be to spend time in a lab practicing configuring, breaking,
and troubleshooting IS-IS. Once you’ve done that, you’ll have the necessary knowledge to work
on IS-IS in a production network.