Re: [v6ops] [IPv6] draft-ietf-6man-rfc6724-update might break current ULA+IPv4 hostnames

[Ole Trøan <[e-mail]>]

Matk,

> On 12 Nov 2023, at 12:19, Mark Smith <[e-mail]> wrote:
> 
> Normally, Host A's ULA address should have a path through the local
> network to Host B's ULA address and vice versa, so Host A and B's ULA
> addresses should be preferred over Host A and Host B's GUA addresses.

Come to think about it. Wouldn’t RFC6724 also fail in the MPMH case?

Source host A with GUA1+GUA2 (from ISPA AND ISPB)
And destination host B with GUA3. 

6724 will return the source address with the longest matching prefix to GUA3. So only one of these:

{GUA1, GUA3}
{GUA2, GUA3}

The SA determines exit path, so depending on which ISP is down. Communication will fail.
Redundancy is the whole point of multi-homing…

The other case I am concerned about is the one where within a single network multiple routers make up their own ULA and use that to assign addresses to directly connected hosts but do not participate in routing. We then have multiple disjointed ULA domains within the network. With RFC7078 and SNAC routers I am not sure if we can avoid that. This would possibly have been cleaner with site-locals.

O.