At 04:50 PM 8/14/2012, Brandon Applegate vociferated:
Hello,
I know this has been mentioned over the years here and there, but I
don't know that I fully understand the exact behavior. I've always
read 'urpf halves your tcam...'.
It applies only to sup2. Sup720 & later don't suffer this limitation.
So this only applies to the interface on which it's configured, correct ?
No. If you turn on uRPF check on sup2 on any interface, the available
FIB TCAM for IP prefixes becomes 50% of what it is without uRPF check.
So for example, in a single switch with the full routing table
(using ipv4 for examples, and using simple even numbers not counting
any built-in entries):
uplink 1 - 400k routes
uplink 2 - 400k routes
customer interface 1 - 2 routes
customer interface 2 - 2 routes
So this is 400,004 entries. Adding (strict) urpf to the customer
interfaces (not the uplinks) would make this 400,008 ?
Well this whole discussion is moot, since you're probably not using
sup2, especially if you have 400K prefixes.
I guess I'm just unsure of if urpf is added to a single interface
(even a customer interface with 1 or 2 prefixes) - does this have
some 'global' effect ?
You're probably confusing the sup2 limit described above, and the
sup720 limitation that all interfaces w/uRPF check have to be in the
same mode (strict or loose) and last configured wins.
Tim
Thanks in advance.
--
Brandon Applegate - CCIE 10273
PGP Key fingerprint:
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Tim Stevenson, tstev...@cisco.com
Routing & Switching CCIE #5561
Distinguished Technical Marketing Engineer, Cisco Nexus 7000
Cisco - http://www.cisco.com
IP Phone: 408-526-6759
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