A lot of times it's the return path that's failing. When you do the
traceroute from another device you have changed the source so it may
have a valid return path.
Not sure what code but you could look at Mini Protocol Analyzer to give
you an inline trace view to watch for the forward and reverse packets:
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/mpa.html
You mentioned equal cost paths so you can look at 'sh mls cef
exact-route srcip dstip' to see whic path the hardware would forward down.
You then need to check the downstream neighbor with some form of packet
capture (netflow, ACL's, etc..) to find out where it's truly lost.
Rodney
On 6/22/10 7:36 PM, Paul Stewart wrote:
Hey folks...
I'm looking for a second set of eyes here ;) Have a pair of 7606 boxes that
have been handling 100's of BGP sessions for a long time now with no
problems (well, performance but I'll leave that alone).
We added a Juniper MX480 into the mix recently and now seem to be having a
routing issue that I can't seem to pinpoint where it's occurring.
Here's a quick rundown to get started of a remote site that is reachable
from other providers and should be reachable from us we'd confident:
traceroute to 216.166.249.148 (216.166.249.148), 30 hops max, 40 byte
packets
1 dis1-rtr-mb-vl10.nexicom.net (216.168.115.177) 0.468 ms 0.477 ms
0.543 ms
2 core2-rtr-to-ge4-12-vl4.nexicom.net (98.124.0.226) 8.803 ms 8.866 ms
8.941 ms
3 * * *
4 * * *
5 * * *
6 * * *
7 * * *
So dis1 is a 6500 and core2 in this case is on the BGP speaking 7606's I was
talking about. Traffic just stops at 98.124.0.226 or the next hop - it's
unclear. So using this destination for example I jump onto core2 and do a
lookup:
core2-rtr-to#sh ip bgp 216.166.249.148
BGP routing table entry for 216.166.248.0/21, version 315975
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Advertised to update-groups:
11 13 17 18 19 22 23
6939 22561
209.51.163.145 from 98.124.59.17 (76.75.100.59)
Origin IGP, localpref 100, valid, internal, best
Community: 11666:1000 11666:1006
6939 22561
209.51.163.145 from 98.124.59.25 (76.75.100.59)
Origin IGP, localpref 100, valid, internal
Community: 11666:1000 11666:1006
You'll see two paths, both valid and both from an iBGP neighbour. The next
hop of 98.124.59.17 is valid and reachable.
If I run a traceroute directly on the core2 7606 box I get timeouts:
core2-rtr-to#traceroute 216.166.249.148
Type escape sequence to abort.
Tracing the route to 216-166-249-148.clec.peknil.commercial.madisonriver.net
(216.166.249.148)
1 * * *
2 * *
Finally, the MX480 where this transit provider connects I do a traceroute
and it's perfect:
[email protected]> traceroute 216.166.249.148
traceroute to 216.166.249.148 (216.166.249.148), 30 hops max, 40 byte
packets
1 gige-g2-20.core1.tor1.he.net (209.51.163.145) 0.458 ms 0.401 ms 0.294
ms
2 10gigabitethernet1-2.core1.nyc5.he.net (72.52.92.165) 21.863 ms 22.573
ms 24.961 ms
3 10gigabitethernet1-4.core1.nyc1.he.net (72.52.92.153) 27.827 ms 18.939
ms 25.197 ms
4 198.32.160.19 (198.32.160.19) 16.381 ms 16.543 ms 16.427 ms
5 bb-nycmny83-jx9-02-ae0-0.core.centurytel.net (208.110.248.114) 27.572
ms 16.578 ms 16.591 ms
MPLS Label=521136 CoS=0 TTL=1 S=1
6 bb-chcgilwu-jx9-02-ae4-0.core.centurytel.net (208.110.248.69) 38.239 ms
38.107 ms 38.254 ms
MPLS Label=570289 CoS=0 TTL=1 S=1
7 bb-mrghmoqa-jx9-02-xe-1-1-0.core.lightcore.net (206.51.69.45) 60.820 ms
45.567 ms 45.416 ms
MPLS Label=656386 CoS=0 TTL=1 S=1
8 bb-peknilxd-jm1-01-ge-0-1-0-298.core.lightcore.net (206.51.69.238)
51.356 ms 51.256 ms 51.440 ms
9 peknil-coe-ci7507-01.grics.net (64.40.75.4) 54.189 ms 53.656 ms
54.102 ms
10 209-102-183-102.nworla.commercial.madisonriver.net (209.102.183.102)
63.918 ms 60.269 ms 60.593 ms
So why is it failing from the Cisco to the Juniper? I'm pulling my hair
(what I have left) out on this ... and it's only happening to a handful of
routes that we are aware of so far....
Thanks,
Paul
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