/128 IPv6 prefixs in the wild?

Mark Tinka mtinka at globaltransit.net
Thu Dec 15 00:30:08 CST 2011


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 
'draft-swallow-mpls-aggregate-fec-01' had gained some 
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?
> 
> 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 
/126.

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 
routers.

Cheers,

Mark.
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