[c-nsp] what happens when the PFC3A fib gets full?

David Sinn dsinn at dsinn.com
Tue Feb 21 11:15:54 EST 2006

You get a nice log message when it happens:

Jan 13 02:35:27 PST: %MLSCEF-DFC3-7-FIB_EXCEPTION: FIB TCAM exception, 
Some entries will be software switched

When it happened to me, a random set of prefix's were black-holed.  I 
didn't get to the root of wether the log message was incorrect (and 
it's not software switched), or if the drops were as a result of 
hitting the MLS rate-limiting that were enabled on the box.  So, your 
milage may vary.


On Feb 20, 2006, at 4:22 PM, Andrew Fort wrote:

> okay, so idiot mode on here: so, what happens when the FIB TCAM gets 
> full..
> box#show ip cef sum | i routes
>   180434 routes, 0 reresolve, 0 unresolved (0 old, 0 new), peak 179402
> (cute how the leaf/route number is above the peak)
> box#show mls cef maximum-routes
> FIB TCAM maximum routes :
> =======================
> Current :-
> -------
>  IPv4 + MPLS         - 192k (default)
>  IPv6 + IP Multicast - 32k (default)
> I know you can re-carve this ('mls cef maximum-routes ...'), which
> obviously requires a reboot.
> My question is, what happens:  does the box just populate what it can,
> causing randomly blackholed prefixes and other nasties, or does it punt
> everything to MSFC, or some combination of the above?
> cheers,
> andrew
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