Re: Confirmation to advance: draft-ietf-6man-ipv6only-flag-05

[Philip Homburg <[e-mail]>]

>I don't propose this, I simply contend that it is what RFC3927 and
>dual-stack model intends. Per Section 2 of RFC 4213, the dual-stack model
>expects dual-stack hosts to be fully compatible with IPv4-Only hosts.

RFC 4213, Section 2.1 starts with:
"Because the nodes support both protocols, IPv6/IPv4 nodes may be
configured with both IPv4 and IPv6 addresses."

Nowhere does RFC 4213 Section 2 say that IPv4 address configuration has to
be the same between IPv4-only and dual stack.

Beyond that, IPv4 is a legacy protocol. There is no reason we can't publish
a RFC that updates a RFC from 2005.

>Further, there are good reasons to require this for compatibility between
>dual-stack hosts and IPv4-Only hosts. If dual-stack hosts were to do as you
>say and not configure a Link-Local IPv4 address if they have a working IPv6
>address they would not be able to communicate with IPv4 Link-Local or
>global scope unicast IPv4 addresses on the local link unless they receive a
>global scope unicast IPv4 address via DHCPv4. Your proposed change breaks
>the dual-stack model.

Please provide examples where people are actively using IPv4 link local
together with IPv6-only in the case the DHCPv4 server fails.

I clearly wrote that the user should be able override this behavior. So if
a site wants to use IPv4 link local to access legacy devices, then the user
would have to change a setting. That's to be expected if you want to use
legacy devices in a modern network.

IPv4 is a legacy protocol. We should not add protocol complexity just to keep
obscure IPv4 features alive.

>By the way, do you mean any working IPv6 address? Because all IPv6 host
>will have an IPv6 Link-Local address. So, do you mean a global scope
>unicast IPv6 address?

Just an IPv6 link-local is not evidence of IPv6 connectivity. My guess is
that checking for any global address is enough. But if a stack wants to
go beyond that and make sure that there is global connectivity and access
to a DNS resolver then that is fine with me.

>Without some kind of explicit signal that a network is intended to be
>IPv6-Only, per Section 2 of RFC4213 a dual-stack host needs to be fully
>compatible with IPv4-Only hosts that could be on the dual-stack network.

There is no need to maintain obscure details of a legacy protocol.

If IPv4 link locals combined with IPv6 are in active use, then obviously that
would make the situation. But, as far as I know, IPv4 link local is
useless, except for some rather obscure edge cases.

For most people, an IPv4 link local just means that DHCP failed. Not some 
thing you use in a network design.