On 28 November 2013 14:56, Mark Andrews <ma...@isc.org> wrote: > > In message > <capkknb6nhr-bcvktwtjf+rfovhyjv0+xycpm6d4cndvzn3f...@mail.gmail.com> > , "Constantine A. Murenin" writes: >> On 28 November 2013 13:07, Leo Vegoda <leo.veg...@icann.org> wrote: >> > Andrew D Kirch wrote: >> > >> > Was I the only one who thought that everything about this was great >> > apart from this comment: >> > >> >> In reality additional poking leads me to believe AT&T gives you a >> > rather >> >> generous /60 >> > >> > Is a /60 what is considered generous these days? I thought a /48 was >> > considered normal and a /56 was considered a bit tight. What prefix >> > lengths are residential access providers handing out by default these >> > days? >> >> Remember, this is just 6rd. With 6rd, a /60 does sound quite generous indeed >> . > > You can hand out /48 as easily with 6rd as you can natively. > > It's only when the ISP is lazy and encodes the entire IPv4 address > space into 6rd thereby wasting most of the IPv6 address space being > used for 6rd that a /60 appears to be generous. > > You can do a 6rd domain per IPv4 allocation. This is a one time > operation that doesn't need to be updated as you move IPv4 address > space around.
This might be true with smaller ISPs, but someone like AT&T probably already has too many distinct IPv4 allocations for such an encoding to be practically manageable. Free, who has pioneered 6rd, and is a major ISP in France, seems to have gone with a similar 6rd allocation policy, giving out /60 through 6rd for each IPv4, out of a /28 IPv6. Seems quite reasonable. http://ripe58.ripe.net/content/presentations/ipv6-free.pdf (So, AT&T simply copied the French here, it would appear.) C. > >> And it's a /60 for each IPv4 you have, e.g. if you have a static IP >> allocation with AT&T U-verse, say, a /27, then you're effectively >> getting a /55 (plus also an additional /60 for the DHCP address in a >> shared subnet to which your /27 is routed to). >> >> That said, I wholeheartedly agree with your comment otherwise. >> >> C. >> > -- > Mark Andrews, ISC > 1 Seymour St., Dundas Valley, NSW 2117, Australia > PHONE: +61 2 9871 4742 INTERNET: ma...@isc.org