BGP Homing Question

Sat Aug 28 04:02:13 UTC 2004

> Patrick W Gilmore wrote:
> There is zero "bad citizenry" in this, and don't
> let anyone tell you differently.

I agree, but not for the reason below:

> It is your netblock, you get to use it as needed.

This is not a good reason; it might be a good excuse, but not a good
reason.

> This is much better than getting another /20 for
> an EU site that only needs a /24.

However, what's above _is_ a good reason. In terms of the size of the
routing table, it does not really matter which two prefixes you
announce, as the simpl(istic) way to see it is that they take two
prefixes anyway. In terms of conservation of the address space it does
matter, as announcing a subnet of your ARIN block in Europe is actually
being a good netizen because it does not waste an ARIN netblock.

> Also, filtering will not be an issue, if you are careful.
> Anyone who does not hear the /24 will hear the /20.

Rick, you do need to tunnel the EU block from your US location back to
your EU location, for people that are behind a filter that masks your
/24. It does not happen often but it does happen. This leads to
suboptimal asymmetric traffic, double whammy in terms of bandwidth
(EU-bound traffic received by the US site from people that see the /20
and not the /24 that has to be re-sent back to EU over the tunnel) and
interesting issues with stateful firewalls though.

Bottom line is: what Rick is suggesting is actually The Right Thing (tm)
to do; the bad netizen would embellish the truth and request a /20 from
RIPE instead, as Patrick mentioned.

Technically speaking, it is sad to say that the bad thing is more
bullet-proof than the right thing though :-( no filtering issues. It's
not nearly as bad as it was a few years ago though, as people have
finally given up on trying to get a full BGP feed on a 3640 with 128
Megs of RAM.

Michel.