BGP prefix filter list

Fri May 31 00:10:42 UTC 2019

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

Uh, because the Internet works? Think about it. If an AS advertises prefixes that can’t be reached through all of its border routers, those prefixes would lose packets.

But I don’t need to provide a citation. The burden of proof is on the person making the assertion, and the assertion by Bill was that having disconnected prefixes in an AS was common. That’s the assertion that needs a citation. My statement is just an opinion that it is clear that  most AS’s are following the standard.

And we’re not talking about single-homed AS’s using private ASNs. Those are definition excluded, because, being single homed, there is only one path to their prefixes.

Any organization that has multiple sites with their own Internet
connections, would then need an AS number for each site.

What are you talking about? Do you use multi homed BGP? If so, I’d expect you to know that an organization with multiple sites having their own Internet still uses a single AS. They have IGP paths to route traffic between sites (e.g., by using dedicated circuits).

 -mel

On May 30, 2019, at 3:55 PM, Thomas Bellman <bellman at nsc.liu.se<mailto:bellman at nsc.liu.se>> wrote:

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
engineering.

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...

   /Bellman

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