/128 IPv6 prefixes in the wild?

Brian Johnson bjohnson at drtel.com
Thu Dec 15 07:56:04 CST 2011


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 at globaltransit.net]
>Sent: Thursday, December 15, 2011 12:30 AM
>To: nanog at 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
>> 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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