aggregation & table entries

Pekka Savola pekkas at
Thu Oct 14 05:05:50 UTC 2004

On Wed, 13 Oct 2004, Randy Bush wrote:
> > The second is a harder problem, because of the business decisions
> > of some providers to source packets from prefixes that they do
> > not announce.
> i presume you are not intending to recommend that i drop packets
> that multi-homed customers hand me when they have also asked me to
> de-pref the prefix from which they come?  i might be their backup
> for inbound, but they need to balance their outbound.

FWIW, (you probably know this, but most on nanog maybe don't),

If you do 'feasible path strict uRPF' as described in BCP84 (I don't
know if others than Juniper are providing that), you can enable strict
uRPF toward those customers, still de-pref them, and accept the
packets with correct source addresses.

That's what we do with our customers whether multihomed or not.

One can also achieve the same without 'feasible path' by operationally
adjusting the weight or preference for the advertisement you receive
w/ eBGP and the advertisement you send in iBGP (so that only that one
router would send its traffic over that link), but that's likely a bit
more work and operational complexity.

Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

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