Route table growth and hardware limits...talk to the filter
Jon Lewis
jlewis at lewis.org
Sun Sep 9 02:07:18 UTC 2007
On Sun, 9 Sep 2007, Randy Bush wrote:
>
>> Maybe this is a dumb question, but why isn't there a BGP option to just
>> filter more specific routes that have the same AS path as the larger
>> aggregate?
>
> i think i filed that request case three or more years ago. zero response.
IIRC, this has come up on cisco-nsp before, and the response has been that
it's very "icky" to do and doesn't really save anything on most platforms.
In the example case of
1) 192.168.0.0/16 AS11111 AS22222 AS33333
2) 192.168.1.0/24 AS11111 AS22222 AS33333
3) 192.168.2.0/24 AS11111 AS55555 AS44444 AS33333
4) 192.168.3.0/24 AS11111 AS22222 AS33333
Forrest says the router should be smart and reject paths 2 and 4 because
they're covered by 1. Now what happens when 1 is revoked? Do we lose
connectivity to 2 and 4, or does the router have to keep track of all
these dependant routes and reinstall 2 and 4 when 1 is lost?
Granted, the overhead involved would maybe be worth it on a platform like
the 6500/7600, where you can end up with a surplus of RAM and not enough
TCAM, if only the "active" routes were stored in TCAM, but it's not
exactly in cisco's best interest to extend the life of gear they'd like to
see replaced with new cisco gear. I just can't understand why they
won't/haven't done a Sup32-3bxl for those using this platform but not
moving enough Gbps to need the traffic capabilities of the Sup720-3bxl.
----------------------------------------------------------------------
Jon Lewis | I route
Senior Network Engineer | therefore you are
Atlantic Net |
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________
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