BGP prefix filter list

Thomas Bellman bellman at
Thu May 30 22:55:21 UTC 2019

On 2019-05-30 20:00 +0000, Mel Beckman wrote:

> I’m sure we can find corner cases, but it’s clear that the vast
> majority of BGP users are following the standard.

"Citation needed". :-)  How is it clear that the vast majority are
following this?

I wouldn't be at all surprised if it *is* literally true; e.g,
quite a lot of BGP users are probably single-homed and thus are
forced to use private ASNs for talking BGP to their ISP; and lots
of BGP users are also single-site, and don't engage in traffic

But those cases are also not very interresting for this.  It is
more interresting to look at those that according to RFC 1930
*should* use multiple ASNs; how many of those *do* have separate
ASNs for each group of prefixes with a "single and clearly defined
routing policy", and how many *don't*?

Any organization that has multiple sites with their own Internet
connections, would then need an AS number for each site.  How many
people follow that?  Can I get multiple ASNs from RIPE/ARIN/et.c
for this case?  (That's an honest question; the policies I found
does mention sites or connected groups of networks, but they also
mention organizations in a way that makes me wonder.)

As others have mentioned, if you do traffic engineering by announcing
prefixes with e.g. different BGP communities, or different amounts of
ASN prefixing, you should according to RFC 1930 get a separate ASN
for each unique combination of communities and ASN prefixing.  Will
RIPE/APNIC/et.c grant us multiple ASNs for that?  I kind of suspect
that we would be told to get lost if we requested 256 ASNs from RIPE
for traffic engineering our /16 into 256 /24:s...


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 836 bytes
Desc: OpenPGP digital signature
URL: <>

More information about the NANOG mailing list