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New Member

mls cef maximum-routes on a SUP7203B

hy guys,

we have an SUP7203B on a 7613 chassis.

we saw that when injecting a large amount of routes (more than 195.000) the following error appears :

%MLSCEF-SP-7-FIB_EXCEPTION: FIB TCAM exception, Some entries will be software switched

when we checked the 'sh mls cef maximum-routes' we saw that the dimension for the IPv4 routes is 192k.

we can tune the TCAM on SUP7203B but we don't know if there will be an impact for

the box performance.

please advise us .


Re: mls cef maximum-routes on a SUP7203B

The error message "%MLSCEF-SP-7-FIB_EXCEPTION: FIB TCAM exception " appears only when no free block is seen.This can be changed using the command mls cef maximum-routes ip.There will be no impact other than a very slight increase in CPU.

New Member

Re: mls cef maximum-routes on a SUP7203B

hello carenas123,

how the resizing of the TCAM could lead to a higher CPU value ?

New Member

Re: mls cef maximum-routes on a SUP7203B

The new configurations are applied after a system reload only and do not take effect if a switchover occurs


Specifying CEF Maximum Routes

To specify the maximum number of routes that can be programmed in the FIB TCAM for a protocol, use the

set mls cef maximum-routes {ip | ip-multicast} routes command.

This command has the following characteristics:

* Changing the setting takes effect only after rebooting the active supervisor engine. The change does not take effect after a switchover.

* The setting on the standby supervisor engine is synchronized with the active supervisor engine. If the standby supervisor is inserted, both the bootup setting and new setting, if existing, on the active supervisor engine are synchronized with the standby supervisor engine. The standby supervisor engine uses the bootup setting to configure the FIB TCAM. The standby supervisor engine might need to be reset if its original bootup setting is different from the bootup setting of the active supervisor engine. An informational message (FIB_MAXROUTES_RESET) is printed on the active supervisor engine console if this situation occurs.

* To maximize the TCAM utilization, we recommend that you set the maximum routes for IP unicast as a multiple of 16,000 and set the maximum routes for IP multicast as a multiple of 8,000. The internal allocation scheme uses 16,000 as the allocation

unit for unicast and 8,000 as the allocation unit for multicast. For example, if IP unicast is set to 1,000, 16,000 entries are reserved, but only 1,000 is allowed.

* When the maximum routes is exceeded or the allocated TCAM space for a protocol is full, a system message (FIB_ALLOC_TCAM_FULL) displays. Because of the internal software allocation scheme, the allocated TCAM space might be full before the maximum routes is exceeded.


If the routes values for all protocols are set to 0, the bootup default is used. When you set the routes value for one protocol to a non-zero value, the default value for the other protocol changes to the remaining size.

If the maximum number of routes is not set for an MLS protocol, a system-determined default value is shown. The default value for a protocol might not be fixed, as the system tries to assign the remaining space to the unassigned protocols. If the maximum-routes configuration is changed after bootup, the show mls cef maximum-routes command displays two kinds of information: one for the current (bootup) configuration and the other for the new configuration that takes effect after reboot.

New Member

Re: mls cef maximum-routes on a SUP7203B

hello mpugliese,

thank u very much for your response. so, if I understood correctly, as long as the number of ip unicast, multicast or mpls routes don't exceed the internal space allocated in TCAM, the risk of

increasing the CPU load is almost zero.