IP ranges, re- announcing 'PA space' via BGP, etc

Fri Apr 7 16:55:41 UTC 2006

Thus spake "Alexander Koch" <efraim at clues.de>
> On Fri, 7 April 2006 07:03:09 -0400, Patrick W. Gilmore wrote:
>> Can you give us some examples so us "dumb Americans" can more
>> precisely explain the problem? :)
>
> When a random customer (content hoster) asks you to accept
> something out of 8/8 that is Level(3) space, and there is no
> route at this moment in the routing table, do you accept it,
> or does Level(3) have some fancy written formal process and
> they get approval to do it, etc.?
>
> In Europe we would tell the customer this ain't gonna happen,
> as we would re- announce blocks out of 'foreign' LIR allocations
> and that is a no-go, unless the holder of that allocations
> acks that.

Here, it seems that some ISPs will accept foreign PA routes* _as long as the 
customer is still connected to that other provider_.  Some won't under any 
circumstances.  The remainder aren't filtering their downstreams and have no 
clue what they are providing transit for (i.e. it's the customer's job to 
get it right).

If you do decide to accept a foreign PA route, you need to be very careful 
to point out to the customer (a) some people will filter your route for 
being too long and send their traffic to the owning provider, and (b) if the 
other provider doesn't announce the longer prefix in addition to their 
aggregate, anyone who accepts the longer route will send traffic only to you 
due to longest match.  Both cases can result in suboptimal routing.

The correct** solution is to help them become an LIR, assuming they qualify.

S

* meaning a route for part of another ISP's aggregate
** for some values of "correct"

Stephen Sprunk        "Stupid people surround themselves with smart
CCIE #3723           people.  Smart people surround themselves with
K5SSS         smart people who disagree with them."  --Aaron Sorkin 