Router ID on IPv6-Only

Crist Clark cjc+nanog at
Fri Sep 9 06:27:01 UTC 2022

As I said in the original email, I realize router IDs just need to be 
unique in
an AS. We could have done random ones with IPv4, but using a well chosen
address assigned to the router guarantees uniqueness as well as some 
other useful
properties. I was wondering if people had some ways to do something 
similar with

But I think the most notable thing from the handful of responses (and 
thanks to
all that responded) was that no one piped up who is actually doing it. I 
most everything is still dual-stack.

And to get even a little more specific about our particular use case and 
suggestion here to build the device location into the ID, we're 
generally not
really talking about one ID per physical router here. I'm really talking 
IPv6-only VRFs. The router (L3 switch, firewall, or whatever it may be) 
have a mix of IPv6-only, IPv4-only, and dual-stack VRFs. I think 
multiple VRFs
per device is no longer exotic configuration and closer to the norm.

And before anyone suggests borrowing IPv4 addresses from other VRFs to 
use in
the IPv6-only VRFs, that was something we discounted right away for what 
I think
are pretty obvious reasons.

On 2022-09-08 08:28, J. Hellenthal wrote:
> Right!
> Personally it just needs to be unique. Relying on a Id to be unique
> when ascociated to an IP address that may be used on a failover system
> seems really poor to me.
> Assign a random ID and plug it into your IPAM!. If at anything assign
> a router ID to a rack location and associate every bit of information
> about that location in whatever you're tracking management can
> provide.
> Personally I prefer date originated generated numbers that allow me to
> filter upon such and spill out the results to tell me where its at
> what rack its in, slot number etc...
> But then again this is from a failover system perspective...
>> On Sep 8, 2022, at 10:13, Randy Bush <randy at> wrote:
>>> 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.
>> arbitrary 32 bit number unique in the autonomous system.  even in an
>> ipv4 world it does not need to match any configured interface address.
>> randy

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