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RE: /128 IPv6 prefixes in the wild?
From: Brian Johnson <bjohnson () drtel com>
Date: Thu, 15 Dec 2011 13:56:04 +0000

I think you will learn a lot of /128s from IGP, but not from eBGP. I consider the "wild" to be the DFZ or similar type 
of network and in that case, you should not see advertisements for anything longer than a /48. This is not hard and 
fast, but please correct me if I'm wrong.

 - Brian J.

-----Original Message-----
From: Mark Tinka [mailto:mtinka () globaltransit net]
Sent: Thursday, December 15, 2011 12:30 AM
To: nanog () nanog org
Subject: Re: /128 IPv6 prefixs in the wild?

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

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

They then establish LSPs and VPN tunnels.


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?

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
/128 addresses because "they only ever need one address" may
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,
not all providers are assigning /64 to interfaces. Some
(like us) are using longer prefix lengths such as /112 and

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



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