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Re: NANOG 40 agenda posted
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
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 !