Le 06-07-04 à 21:12, Christian Huitema a écrit :
What would be the purpose of filtering at /48? That allows for 2^45 = 351 trillion prefixes in the routing table, which I suspect won't work too well on current routers. And it only takes a handful of /32s deaggregated into /48s to inflate the IPv6 global routing table to a size larger than the current IPv4 routing table.But then, filtering at /32 allows for 2^30 = 1 billion prefixes, which Isuspect also won't work too well on current routers. Setting filtering constraints at /32 is not sufficient to ensure small tables.
yeap.
Setting narrow filtering constraints is also counter-productive, as itencourage a rush on the short prefixes. An organization that could havedone just fine with a /48 or maybe a /40 will request a /32 just in case, so that organization can eventually multi-home. In the end, the size of the routing table will equal the number ofentities that want multi-homing hard enough. Playing around with prefixsizes will not change that, and will probably generate undesirable counter effects.Besides, there are networks in which advertizing /48 or even /64 in BGP makes perfect sense. Take for example the "metropolitan aggregation" inwhich all users in an area get numbered from the same long prefix. Thelocal ISP will have to exchange the short prefixes with each other. Thewill use BGP. Do we want to have a rule cast in stone that prevents them?
fine. however, the "global routing table" should not see these. Hence back to the minimal requirement to filter at least anything longer than /48.
We should really think twice before asking the IETF to publish a position on this subject. Silence may well be the right approach.
I think it is reasonable and good stewardship to define the longest prefix possible in the global routing table (/48). Then anything smaller is subject of policies and is probably more contentious to write.
Marc.
-- Christian Huitema
========= IPv6 book: Migrating to IPv6, Wiley, 2006. http://www.ipv6book.ca