AT&T UVERSE Native IPv6, a HOWTO
marka at isc.org
Fri Nov 29 01:04:51 UTC 2013
In message <CAPKkNb6nCnP3Xk4xrLhvoiYBivw7pj3ggU3-bonxoTCBUYpUGA at mail.gmail.com>, "Constantine A. Murenin" writes:
> On 28 November 2013 14:56, Mark Andrews <marka at isc.org> wrote:
> > In message <CAPKkNb6Nhr-bcvkTwTjf+rFovhYjv0+xyCPM6D4CndvZn3FqeA at mail.gmail.com>
> > , "Constantine A. Murenin" writes:
> >> On 28 November 2013 13:07, Leo Vegoda <leo.vegoda at 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.
If you are going with /48's
For each IPv4 /8 they have been allocated they carve out a IPv6 /24 for it.
For each IPv4 /22 they have been allocated they carve out a IPv6 /38 for it.
If you are going with /56's
For each IPv4 /8 they have been allocated they carve out a IPv6 /32 for it.
For each IPv4 /22 they have been allocated they carve out a IPv6 /46 for it.
Carving out smaller blocks from bigger blocks is what ISP's do all
the time when allocating space for customers and unlike customers
this doesn't have to be done over and over again. It is a once off
when they receive the address block regardless of how they later
split up and move around the IPv4 address block.
> 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.
> (So, AT&T simply copied the French here, it would appear.)
Just because someone does one way it doesn't make them right or
correct. It just means they did it that way. This is saying "my
customers will *never* have more that 16 subnets" which is possible
true in the short term for home users but not for companies. Think
how many vlans companies use today. Each of those vlans should be
getting a /64.
It is short sighted decisions like this which force companies into
using NATs whether they want to or not.
> >> 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 at isc.org
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: marka at isc.org
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