From: Iljitsch van Beijnum (no email)
Date: Mon Jun 04 2007 - 05:30:00 EDT
On 2-jun-2007, at 23:07, Donald Stahl wrote:
>> The simplistic answer is that nearly all assigned/allocated blocks
>> will be minimum-sized, which means ISPs will be capable of
>> filtering deaggregates if they wish. Some folks have proposed
>> allowing a few extra bits for routes with short AS_PATHs to allow
>> TE to extend a few ASes away without impacting the entire community.
> This is an excellent solution- is there some reason people wouldn't
> want to implement it? It would seem to lead directly to a more
> heirarchical table.
I proposed something in a similar vein in a draft for the IETF v6ops
working group: in order to allow people to multihome using PA space
(which some people want to avoid having to deal directly with a RIR
or for other reasons best known to themselves) there would be well-
known community that indicates that a prefix is present in the
routing table by design and not because of random deaggregation, and
that it's part of an aggregate so it's ok to filter it out when it
reaches a certain AS path length.
See http://www.muada.com/drafts/draft-van-beijnum-v6ops-pa-mhome-
community-01.txt
and http://www.bgpexpert.com/presentations/multihoming_paspace.pdf
Then I created the filter that has to do this work and I started
having doubts about the practical deployability of something like
this... The config below doesn't even look at AS path lengths:
!
ipv6 prefix-list except-apnic seq 5 permit 2001:7fa::/32 le 64
ipv6 prefix-list except-arin seq 5 permit 2001:500::/29 le 48
ipv6 prefix-list except-lacnic seq 5 permit 2001:1200::/23 le 48
ipv6 prefix-list except-ripe seq 5 permit 2001:600::/23 le 64
ipv6 prefix-list global-pa seq 5 permit 2000::/3 le 32
ipv6 prefix-list global-pa-mhome seq 5 permit 2000::/3 le 56
!
ip community-list standard mhome-cty permit 1:1
!
route-map import permit 10
match ipv6 address except-apnic
!
route-map import permit 20
match ipv6 address except-lacnic
!
route-map import permit 30
match ipv6 address except-ripe
!
route-map import permit 40
match ipv6 address except-arin
!
route-map import permit 60
match community mhome-cty
match ip address global-pa-mhome
!
route-map import permit 70
match ip address global-pa
!
|
|
|