Re: [6bed4-devel] Comments and thoughts on bed64

[<ebi...@xm...>]

Rick van Rein <ri...@op...> writes:

>> - Interface identifiers:
>>   I suggest  you simply drop the concept of illegal port values
>>   Only going through an interface that strongly assumes ethernet
>>   will they even that even be a problem.  And making some port
>>   numbers illegal looks like a good way to break in surprising ways
>>   on weird NAT implementations.
>
> Note that odd *external* UDP ports are said to be illegal.  This is at
> the outside of NAT.
>
> The reason to ban odd port numbers on all nodes is to be able to show
> one's address to a node that assumes ethernet semantics for the 6bed4
> interface.  It seems a waste to disable interoperability with existing
> stacks; this is why odd external UDP ports are banned.
>
> This is not a conceptual beauty, but it is the sort of pragmatics that
> I'm willing to incorporate because 6bed4 is a transitional technique.

The trade off is breaking some clients in myserious ways, instead of
implementing an indirection table mapping mac addresses to ipv4 address
and ports.

Banning odd ports is a BAD idea.  It means hosts will not be able to
assume they have a working 6bed4 tunnel.  Your reference implementation
does not even handle the case when the NAT takes your even port and
gives you an odd port.  It is a bug you won't find in testing, it is a
bug that will make people decide your protocol is flaky and deprecate
it.

So I disagree with the restriction to only use even ports in the
strongest possible terms.

On the flip side you can interoperate as ethernet with existing stacks
with one simple layer of indirection.  You can go farther and do a clean
implemenation that doesn't claim to be eithernet and not even need that
layer of indirection.  But for the sake of a bit I don't want to see
a protocol lost.

Eric