FIB Exception error Cisco6500, Sup720-3BXL Please help!

Answered Question
Jul 1st, 2008
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Hi everyone,

I have a Cisco 6509 w/ Sup720-3BXL. Upon bootup, and receiving 2x full internet BGP tables (250K routes each) from 2 different ISPs, an then sending the full tables to 6 ibgp peers and receiving approximately 700 prefixes total from the 6 i bgp peers.

The router starts with the following error:

MLSCEF-DFC4-4-FIB_EXCEPTION: FIB TCAM exception for IPv4 unicast, Some routes will be software switched.Use "mls cef maximum-routes" to modify FIB TCAM partition

At that time, the router starts to switch things in software and I can see the BGP out Queues for the ibgp peers have like 800, and cpu spikes to 99-100% for hours unless I reboot the router.

I have already done "mls cef maximum-routes 239K"

I do have 4x 8port 1gb etherchannels connected to this router (each is for a iBGP peer), with 2 route-maps applied to the interfaces if that makes any difference.

The Router is pushing about 15gb of traffic.

Running: s72033-advipservicesk9_wan-mz.122-18.SXF9.bin

Please, any help is greatly appreciated.

Thank you so much.

Correct Answer by a.alekseev about 8 years 10 months ago

just remove card with dfc3a


and see the output "sh mls cef maximum-routes"

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Overall Rating: 5 (1 ratings)
tstanik Mon, 07/07/2008 - 09:39
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Regarding the error message, there is the maximum number of the routes that can be programmed in particular hardware. If routes are detected that exceed the limit for that protocol, an exception condition is generated. Can you please configure the following command to increase the max routes size:

Router(config)#mls cef maximum-routes ip ?

<1-239> number of 1K entries

You can increase the max ip routes to 239. At this point you have 200K.

gskhanna Mon, 07/07/2008 - 10:36
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I wrote above,

I have already done "mls cef maximum-routes 239K"

That was already done.

How many full routing tables can a sup720 1gb hold?

tsillaber Tue, 07/08/2008 - 09:36
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You can check the maximum routes with

sh mls cef maximum-routes

Also check the active routes

show mls cef summ

How many routes are active, when cat6k switch to sw forwarding?

gskhanna Tue, 07/08/2008 - 13:39
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Core-1#sh mls cef maximum-routes

FIB TCAM maximum routes :


Current :-


IPv4 - 239k

MPLS - 1k (default)

IPv6 + IP Multicast - 8k (default)

Core-1#show mls cef summ

Total routes: 56333

IPv4 unicast routes: 56306

IPv4 Multicast routes: 3

MPLS routes: 0

IPv6 unicast routes: 24

IPv6 multicast routes: 0

EoM routes: 0

I did not do these commands during the time of the issue. I do know it was already set to 239K for maximum. However I'm not sure what the active was. I can try it again this saturday during our maintenance window.

I did remove 1 provider from it, hopefully that will help as well.

a.alekseev Tue, 07/08/2008 - 09:46
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could you show the output

sh mod

gskhanna Tue, 07/08/2008 - 13:40
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Core-1#sh mod

Mod Ports Card Type Model Serial No.

--- ----- -------------------------------------- ------------------ -----------

2 48 CEF720 48 port 1000mb SFP WS-X6748-SFP SALxxxxx000

3 4 CEF720 4 port 10-Gigabit Ethernet WS-X6704-10GE SALxxxxxGJQ

4 48 CEF720 48 port 10/100/1000mb Ethernet WS-X6748-GE-TX SALxxxxx19A

6 2 Supervisor Engine 720 (Active) WS-SUP720-3BXL SALxxxxxQTA

Mod MAC addresses Hw Fw Sw Status

--- ---------------------------------- ------ ------------ ------------ -------

2 0018.b98d.cf6c to 0018.b98d.cf9b 1.8 12.2(14r)S5 12.2(18)SXF9 Ok

3 0013.1972.548c to 0013.1972.548f 2.3 12.2(14r)S5 12.2(18)SXF9 Ok

4 0013.80c1.7840 to 0013.80c1.786f 2.2 12.2(14r)S5 12.2(18)SXF9 Ok

6 0013.7f0a.ed80 to 0013.7f0a.ed83 4.3 8.1(3) 12.2(18)SXF9 Ok

Mod Sub-Module Model Serial Hw Status

---- --------------------------- ------------------ ----------- ------- -------

2 Centralized Forwarding Card WS-F6700-CFC SALxxxxx3RM 3.0 Ok

3 Distributed Forwarding Card WS-F6700-DFC3BXL SADxxxxx2X6 5.3 Ok

4 Distributed Forwarding Card WS-F6700-DFC3A SALxxxxxVJ4 2.2 Ok

6 Policy Feature Card 3 WS-F6K-PFC3BXL SALxxxxxG0P 1.6 Ok

6 MSFC3 Daughterboard WS-SUP720 SALxxxxxMJV 2.3 Ok

Mod Online Diag Status

---- -------------------

2 Pass

3 Pass

4 Pass

6 Pass

Should be the correct hardware for what I'm saying/using? :)

gskhanna Tue, 07/08/2008 - 18:31
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By just having that card in the router decreases the entire performance? That blade is actually not in use even. I can remove it, but why wouldn't it still have enough cpu/ram to handle full routing table from 2 ebgp peers, and 6 ibgp peers?


a.alekseev Wed, 07/09/2008 - 23:11
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Have you tryed to remove card with dfc3a and relod the router?

gskhanna Wed, 07/09/2008 - 23:20
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We will be doing it on Friday night. I'll let you know how it goes.


Correct Answer
a.alekseev Wed, 07/09/2008 - 23:23
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just remove card with dfc3a


and see the output "sh mls cef maximum-routes"

gskhanna Sat, 07/12/2008 - 00:38
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yep that was the issue!

Thank you very much for your help. Removed the blade, and now it does 512K default, or up to 1000K (1million routes) as it was supposed to.

Thanks again!


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