[c-nsp] BGP confusion in 12.2(18)SXE2

Gert Doering gert at greenie.muc.de
Tue Sep 13 18:12:11 EDT 2005


Hi,

I was adventurous (or maybe "stupid") enough to run 12.2(18)SXE on our
Sup720 based router things.

Yesterday BGP started acting up in *very* interesting ways ("show ip b su"
claimed to have seen "50" prefixes from a given peer, while the detailed
commands, like "show ip b neigh x.x.x.x received-routes" displayed 
*one* prefix, or just a hand ful).  

After clearing all neighbours on the box (very nice thing to do on a 
router that does "core + major peering point") everything seemed to be
normal, but today I noticed another funny:

Cisco#sh ip b 4.0.0.0   
BGP routing table entry for 4.0.0.0/8, version 15607368
Paths: (5 available, best #2, table Default-IP-Routing-Table)
        ^^ it says "5" here

  Advertised to update-groups:
     3         
  1273 3356, (aggregated by 3356 4.68.0.8)
    208.175.XX.YY (metric 172800) from 193.149.XX.YY (193.149.XX.YY)
      Origin IGP, metric 1, localpref 100, valid, internal, atomic-aggregate
  1273 3356, (aggregated by 3356 4.68.0.8)
    62.208.XX.YY (metric 156416) from 193.149.XX.YY (193.149.XX.YY)
      Origin IGP, metric 1, localpref 100, valid, internal, atomic-aggregate, best
  13237 6461 3356, (aggregated by 3356 4.68.0.8)
    217.71.XX.YY from 217.71.XX.YY (80.86.XX.YY)
      Origin IGP, metric 1, localpref 100, valid, external, atomic-aggregate

... and then lists *3* paths.

This happens for just about any prefix learned from external sources
(the number of actual paths varies, but it always displays less
paths than given in the summary line).

Has anyone of you seen this before?  Is this a known issue in SXE2?

I *think* this started happening when I changed the "full eBGP feed"
session connected to this router to "no neighbour 217.71.xx.yy soft in"
- at least that's when our customers started yelling at us... - but
I've done this to various routers in the past, and never seen such 
strange BGP behaviour...

We're running various 7200s with 12.2(18)S<n>, and these never did 
funny BGP things - so I'm a bit confused whether 12.2(18)SXE2 has the
same BGP code, or maybe something completely different?

gert

-- 
USENET is *not* the non-clickable part of WWW!
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de


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