[c-nsp] Bad routes in MPLS

Saku Ytti saku at ytti.fi
Sat Nov 23 16:10:12 EST 2013


On (2013-11-23 12:35 -0800), Tony wrote:

> --- At this point my ping started responding, but CEF details look strange. MTU is set to 1036 and packets/bytes counters are zero !?

You don't seem to run BCP MLS rate-limiters :). People who don't miss out lot
of fun debugging, as 'minor' misprograms like these are not noticed.

What happens here, packet is punted from HW to SW, so SW can generate ICMP
message about too large packet. However,  SW likely had correct information,
so it just forwarded it normally. If you had ran BCP MLS rate-limiters, your
MTU-error punts would have been ratelimited to silly low values, and you'd
notice packet loss.

> --- The pings are still working and now the CEF entry "looks" correct - MTU is OK and counters are incrementing. The other slightly strange thing is that when I did it the first time the adjacency entry number changed, but the 2nd time it didn't (stayed at 311374).

IF you have DFC, you also need to give module number for these commands. I
would also have been interested in flags of the adjacency.

But maybe next time, before fixing it (as MLS CEF looked ok to me), run ELAM
capture to see what platform claims to be doing to it. Superman capture is
very very easy and useful, with Tycho you'll need some acrobatics to capture
the packet you're interested in.

-- 
  ++ytti


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