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

[Fernando Gont <[e-mail]>]

On 13/5/19 11:08, Philip Homburg wrote:
>> 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.

Actually, in IPv6-only or failing-DHCPv4-server scenarios, some hosts
will normally configure ipv4 link-locals... which will normally be used
when doing e.g service discovery.


> 
> 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.

Most usually, it's not sites that decide to use link-locals, but hosts.
-- it's a host-side policy that is *not* selected or configured on a
per-network basis.

That said, in all cases, I expect the network to "just work". Users
should not be required to understand this sort of technical details for
them to get a good experience.


Thanks,

-- 
Fernando Gont
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