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Tuesday, November 15, 2011

Cisco 7609 RSP720-3CXL-GE "mls cef maximum-routes"

We receive syslog warnings that we run to the threshold for the maximum supported mpls routes in the CEF table, below some information.
What is the impact/risc if the threshold is exceeded?
What is the service impact when increasing the settings?
What do we do with the redundant sup720?
is there some good documentation on this? in particular the RSP720-3CXL-GE (I found some old stuff on CATOS and sup32)
ASDGTS1CRT01#sh mls cef maximum-routes
FIB TCAM maximum routes :
Current :-
IPv4 - 450k
MPLS - 384k
IPv6 + IP Multicast - 88k (default)
ASDGTS1CRT01#sh mls cef sum
Total routes: 750214
IPv4 unicast routes: 375897
IPv4 Multicast routes: 3
MPLS routes: 374036
IPv6 unicast routes: 0
IPv6 multicast routes: 0
EoM routes: 278

Actually RSP720-3CXL can get up to 1M of IPv4 +MPLS routes. Your current values are 450k+384K=834K. So you have some room to increase that:
- Theoretically this maximum number of routes can be adjusted by the following commands:
mls cef maximum-routes ip 500
mls cef maximum-routes mpls 500
500 or any number that can support all the routes.
- Please be aware that if we change the maximum number of IPv4 + MPLS routes to 1M, there will be little resource for IPv6 and Multicast.
IPv4 - 500k
MPLS - 500k
IPv6 + IP Multicast - 8k (default)
- Also changing that you can exaust all available memory in TCAM. In some cases that can lead to CEF auto switch off to resume the normal operation of router. In turn this can lead for packets to be processed switched. So fine tuning should be done accurately.

- If total is below the Processor limit - then CEF just stop storing routes above limit to TCAM - and those can be software switched increasing CPU load. If it will be close to physical limit - then memory can be exausted and in some corner cases CEF can be auto switched off to resume normal operation of router.

- you need to reload to apply changes, also reaching the maximum limits can sometime lead to CEF problems due to no memory

- Redundant SUP does not participate in control plane decisions - it just synch it's state with active one. Nothing more

Whole reload needed as this should be populated to TCAM.
If you just reload standby - it would still get in synch with active and get current TCAM values from it thus your changes will not be applied. Thus Maintenance Window should be organized for that. But I would also start checking the routes - if there is any possibility to remove some. You don't have too much room for TCAM increase so might soon get it filled as well and then you ill reach HW limit. So possibly a good chance to start revising those now.
Though that is really depends on your NW.

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