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.

On Thu, 15 Dec 2011, Glen Kent wrote:

In the service provider networks, would we usually see a large number of /128 prefixs in the v6 FIB tables?

If you have /128s on the loopbacks of your routers, your other routers could learn the /128s for the loopbacks of your other routers through your IGP.

What are the scenarios when IPv6 routers would learn a large number of /128 prefixes?

Two questions: 1. What is a 'large number' in this case? 2. Are the addresses from your v6 range(s), or something else that wouldn't be coming from the outside world (link-local, etc)?

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?

Looking at the routing table on one of my lab routers, I only see the /64 for a remote network in its v6 routing table, along with the interface and link-local address of the router it wants to use to reach that destination. I do not see any separate entries for any smaller chunks of that /64. jms