[101693] in North American Network Operators' Group
Re: BGP Filtering
daemon@ATHENA.MIT.EDU (Deepak Jain)
Tue Jan 15 17:09:48 2008
Date: Tue, 15 Jan 2008 17:08:52 -0500
From: Deepak Jain <deepak@ai.net>
Reply-To: deepak@ai.net
To: Ben Butler <ben.butler@c2internet.net>
CC: nanog@merit.edu
In-Reply-To: <F9181128E9584B40B5A04C43800604B406DCD9@anyanka.c2internet.net>
Errors-To: owner-nanog@merit.edu
> But if I can see the /19 in the table, do I care about a load of /24s
> because the whole of the /19 should be reachable as the origin AS is
> announcing it somewhere in their network and it is being received my a
> transit so should be reachable.
The "presumption" in cases like this is that the /24 may take a
different path than the /19 in some or all cases. If you have only a
single provider you can safely dump more specifics -- but then, you
could just point default. If you *are* multihomed and the /19 and /24
both have the same primacy (first choice in a routing decision and same
path) you can safely drop the more specific.
The "presumption" is that in some cases the /24 would take a different
path than the /19 in a routing fight.
How much cost you want to incur for these is your choice. If enough
people drop the more specifics, they will go away as well -- if they
provided no benefit, fewer would exist.
Some of this originates from the peering-contests where folks have "x
number of prefixes" which makes them bigger than "y number of prefixes".
I'd be interested to see any metrics on rate of growth of allocations
longer than RIR limits since Verio instituted then dropped mandatory
prefix filters. (vs the rate of growth of prefixes overall). I would
guess that they accelerated.
Deepak
