Code change:
stub router MUST treat the prefix as unsuitable and allocate a ULA Link Prefix out of its ULA Site Prefix instead. <ins> A DHCPv6-PD client can request a particular lease interval for the DHCPv6-delegated prefix.  However, there is no particular reason for a SNAC router to specify this interval. 5.2.3.1. It is possible that a SNAC router might obtain a prefix from a DHCPv6 server using prefix delegation and then something about the infrastructure network attachment might change that affects the validity of that prefix for use on the stub network.  The section of I-D.ietf-dhc-rfc8415bis titled "Refreshing Configuration Information" discusses the various scenarios that can occur.  We assume that the DHCPv6 prefix delegation client being used by the SNAC router conforms to this specification. Situations that can occur include (but are not limited to): The SNAC router MUST NOT use a prefix once the DHCPv6-PD client has determined that it is no longer valid.  If the DHCPv6-PD client provides a new prefix, and the old prefix is still valid, the SNAC router SHOULD explicitly deprecate the old prefix at the same time that it first advertises the new prefix. If the DHCPv6-PD client determines that the prefix it provided to use as the OSNR prefix is no longer valid, and no replacement prefix is provided by the DHCPv6 server, then the SNAC router MUST switch to the ULA link prefix that it has allocated for use on the SNAC network.  In the case that the DHCPv6-PD client is unable to renew its lease on the current OSNR prefix, and time between the T2 interval for the prefix assignment I-D.ietf-dhc-rfc8415bis and the end of the lease has been reached, then the SNAC router MUST deprecate the DHCPv6-PD-provided OSNR prefix and begin advertising the ULA link prefix. A failure to renew the DHCPv6-PD-provided OSNR prefix could be because the SNAC network has been disconnected from one AIL and moved to a different AIL.  In this situation, if the new AIL also has IPv6 service and DHCPv6-PD service, the DHCPv6 client will get a clear indication that the old prefix is no longer valid.  However, it may be that no DHCPv6-PD service is available on the new link, either because it is an IPv4-only link or because it's an IPv6-capable link that doesn't provide DHCPv6 service.  In this situation, if the SNAC network remains connected to the link and no DHCPv6 service appears, the DHCPv6-PD-provided OSNR prefix will eventually time out and be replaced.  The SNAC router SHOULD NOT attempt to replace it prior to this normal timeout process, because there is no benefit to changing the OSNR prefix on the SNAC network in such a situation, and it's possible that the SNAC router will return to the other link before the OSNR prefix expires. </ins> 5.3. Stub routers MUST advertise reachability to stub network OSNR

Related discussion:
text: Closing issue This PR is not building, so need to clean it up before commit. Comments appreciated during that process.
NAME PR is still needed before anything can build ;-)
NAME NAME sorry I didn't intend to close this PR, Github did that somehow after me pushing to the branch. But it's good to have this one closed and replaced by , because the merge direction was specified here the wrong way around. The build is now fixed in the branch and also updated to make it merge-able into main. I prefer to merge rather sooner than later - nits can be corrected with future PRs easily.