[147583] in North American Network Operators' Group

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Re: /128 IPv6 prefixs in the wild?

daemon@ATHENA.MIT.EDU (Mark Tinka)
Thu Dec 15 01:31:31 2011

From: Mark Tinka <mtinka@globaltransit.net>
To: nanog@nanog.org
Date: Thu, 15 Dec 2011 14:30:08 +0800
In-Reply-To: <CAPLq3UPwo0j3QDiSJLqsoOOPzaN_xmGyyzLGfic_DEC2H6mSRg@mail.gmail.com>
Reply-To: mtinka@globaltransit.net
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org

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On Thursday, December 15, 2011 01:54:56 PM Glen Kent wrote:

> In an IP/MPLS world, core routers in the service provider
> network learn the /32 loopback IPv4 addresses so that
> they can establish BGP/Targetted LDP sessions with
> those.

That's right - not sure how things would have been if=20
'draft-swallow-mpls-aggregate-fec-01' had gained some=20
traction.

> They then establish LSPs and VPN tunnels.

Indeed.

> Since
> we dont have RSVP for IPv6 and LDP for IPv6 (not yet
> RFC) we cannot form MPLS tunnels in a pure IPv6 only
> network. GIven this, would v6 routers have large number
> of /128 prefixes?
>=20
> What are the scenarios when IPv6 routers would learn a
> large number of /128 prefixes?

I suspect ISP's that choose to assign broadband customers=20
/128 addresses because "they only ever need one address" may=20
be a situation where you see rise given to this.

> I would presume that most IPv6 prefixes that the routers
> have to install are less than /64, since the latter 64
> is the host part. Is this correct?

This is certainly going to re-open some "wounds", but no,=20
not all providers are assigning /64 to interfaces. Some=20
(like us) are using longer prefix lengths such as /112 and=20
/126.

But as for /128 prefix lengths, aside from the fact that=20
Loopbacks will be floating around the network, whether=20
you're using them to signal MPLS LSP's or setup iBGP=20
sessions, you will see them with ISP's that assign them to=20
customers and choose not to aggregate them at specific edge=20
routers.

Cheers,

Mark.

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