On 28 November 2013 14:56, Mark Andrews <marka@isc.org> wrote:
In message <CAPKkNb6Nhr-bcvkTwTjf+rFovhYjv0+xyCPM6D4CndvZn3FqeA@mail.gmail.com> , "Constantine A. Murenin" writes:
On 28 November 2013 13:07, Leo Vegoda <leo.vegoda@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: marka@isc.org