I was wondering if I could get some additional opinions on a case I have
open with Cisco. We have recently started turning up LDP on various
links out towards some routers that are being converted to act as PEs.
The core is all connected together and has been running LDP on those
particular links for over 8 months.
This past weekend we turned up LDP on a link to one of our remote cities
and we received sporadic complaints that some customers couldn't access
any sites/addresses if the path was via one of our P routers. If
traffic was through any other path on the network it was fine.
Traceroutes to & from this P router showed were unsuccessful even though
the routing table and LFIB all showed the correct information. Turning
off LDP across this link resolved the problem for the customers.
After opening up the TAC case and lots of troubleshooting they showed us
this:
Without LDP on:
frort04#sh ip cef exact-route 172.17.0.254 68.179.73.86
172.17.0.254 -> 68.179.73.86 : Vlan2210 (next hop 67.226.181.110)
<<<<<< the next hop is correct
With LDP on:
frort04#sh mls cef exact-route 172.17.0.254 68.179.73.86
Interface: Vl2210, Next Hop: 224.0.0.168, Vlan: 2210, Destination Mac:
00b0.4a5e.7419 <<<<<<<< next hop can't be a multicast IP
the CEF entry and MLS CEF entry are different, after consulting the
LAN-SW team, it is found this router had issue of overloaded routes
causing mls cef table become corrupted.
So basically we were told that because the SUP32 has a hardware
limitation of 250K routes that it can hardware cef, we were getting
corruption in our tables and in turn corrupting how LDP was building its
forwarding table. The core P routers currently hold the entire internet
routing tables so yes they technically are pretty full in terms of the
number of routes they can hold. They want us to reload our router to
clear the tables but they can't guarantee that this problem won't
resurface again down the road or right away. I'm more curious if there
is some kind of IOS bug we might be hitting which I'm hoping one of you
might know but they're supposed to be doing a bug scrub as well.
Any thoughts on what we're experiencing? Should we bite the bullet and
upgrade to SUP720-3BXLs?
Thanks.
Jose
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