RE: Router ID on IPv6-Only

[Paul Amaral via NANOG <nanog () nanog org>]

Is there really such as thing as pure IPV6 only? I don’t think you will be able to run IPV6 for transport without the 
router locally knowing how to handle IPV4, at least not right now as there’s a lot of legacy code. Usually IPV6 is 
enabled longer after IPV4 has been running. With that said, can’t you just enable ipv4 and not route it passed the 
router, then use RFC1918 to manually general your 32 bit ID.

 

Paul 

 

From: NANOG <nanog-bounces+razor=meganet.net () nanog org> On Behalf Of Crist Clark
Sent: Thursday, September 8, 2022 1:39 AM
To: nanog () nanog org list <nanog () nanog org>
Subject: Router ID on IPv6-Only

 

During some IPv6 numbering discussions at work today, someone had a question that I hadn't really considered before. 
How to choose 32-bit router IDs for IPv6-only routers.

 

Quick background. We have a requirement to convert a significant portion of our network to IPv6-only over the next few 
years. Previously, I, and everyone else on the team, have only ever set up routers in dual-stack environments. Choosing 
a router ID for use in routing protocols just followed whatever rules you used for your IPv4 networking. You used the 
same router ID in IPv4 and IPv6.

 

Well, now there is no IPv4. But BGP, OSPFv3, and other routing protocols still use 32-bit router IDs for IPv6. On the 
one hand, there are plenty of 32-bit numbers to use. Generally speaking, router IDs just need to be unique inside of an 
AS to do their job, but (a) for humans or automation to generate them and (b) to easily recognize them, it's convenient 
to have some algorithm or methodology for assigning them.

 

Has anyone thought about this or have a good way to do it? We had ideas like use bits 32-63 from an interface. Seems 
like it could work, but also could totally break down if we're using >64-bit prefixes for things like router-to-router 
links or pulling router loopbacks out of a common /64.

 

Also, various network OS implementations will typically automatically choose a router ID from the IPv4 addresses on the 
router by some algorithm (e.g. numerically lowest) if not explicitly configured. Was curious what IPv6-only routers do. 
Haven't had the chance to get on some lab gear or GNS3 to just try it and see.