On 4/1/2015 11:36 AM, John R Levine wrote:
>> Didn't we stalemate on the question of whether this has to be a whole new
>> header field, or a "v=" increase? I seem to recall someone (Dave?)
>> thinking both were horrible.
>
> That was certainly a question, but I don't recall any consensus on
> realtive horribility. I like v=2, that's what version bumps are for.
Version numbers are superfluous or inappropriate overhead. That is,
they are either useless or else the wrong solution to demultiplexing
amongst alternate protocols.
When a protocol is revised, there are two possibilities:
Upward Compatible: The old version of the protocol interworks with
the new version. So the new protocol is a superset of the old. In this
case, the enhancements typically self-identify, as new parameters or new
values for existing parameters.
Incompatible: The old and new don't interwork.
In the first case, the version field is literally useless. It is wholly
redundant or worse insufficient, given that the receiver of the protocol
data unit sees the new stuff in other ways than the version field.
In the latter case, it's really an entirely new protocol, which should
be identified by the next-lower protocol, rather than by using the
version field as an in-bred demultiplexing field.
And yes, IPv4 and IPv6 are distinguished by different demultiplexing
values in the Ethernet frame:
http://en.wikipedia.org/wiki/EtherType
d/
--
Dave Crocker
Brandenburg InternetWorking
bbiw.net
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