[c-nsp] Hardware limitations on SUP32 with LDP and full routing table

[Marek Tyban]

Hi Jose,

I think that generally SUP32 isn't suitable for todays full internet 
routing table. It's due to the hardware limitations (as you wrote).

When you have full routes on SUP32 you should see log output as below

%MLSCEF-SP-4-FIB_EXCEPTION_THRESHOLD: Hardware CEF entry usage is at 95% 
capacity for IPv4 unicast protocol.

%CFIB-SP-7-CFIB_EXCEPTION: FIB TCAM exception, Some entries will be 
software switched

I have seen similar troubles with some sites/networks weren't reachable 
throught SUP720-3B (non XL) routers, but the routing and CEF table were 
correct.

Regards,
Marek

On Wed, 21 Jan 2009, Jose wrote:

> 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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