[IPsec] Draft-ietf-ipsecme-ipv6-ipv4-codes

[Tero Kivinen <[e-mail]>]

In the Prague meeting we had two options how to send information what
kind of address families are supported [1]:

1) IP6_ONLY_ALLOWED and IP4_ONLY_ALLOWED status notifications which
   are sent whenever only one address family is supported. I.e., if
   only one address family is supported, then IP*_ONLY_ALLOWED is
   sent. If both address families are supported, then no status code
   is sent. This is what current draft proposes.

2) ADDITINAL_ADDRESS_FAMILY_POSSIBLE status notification which is used
   when other address family than currently returned could also be
   used. I.e., if no address was assigned, then this status
   notification tells that trying with other address family works, and
   if address was assigned from one address family this tells that
   another request with another address family can also work. 

In the meeting we did not have clear concensus [2] on which of them
are better. The option 2 is closer to what we currently have in
RFC7296 for ADDITIONAL_TS_POSSIBLE.

Both of the options seems to work, and I think people think the
differences are so small, that they do not care. So unless people
object soon, I think we will keep whatever is in the draft, as I
seemed to be only one who thought the other option would be clearer.

[1] See slides 6 and 7 of
    https://datatracker.ietf.org/meeting/104/materials/slides-104-ipsecme-chair-slides-04
[2] https://datatracker.ietf.org/doc/minutes-104-ipsecme/
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