[e2e] Port numbers in the network layer?

Hagen Paul Pfeifer hagen at jauu.net
Thu Apr 25 12:56:25 PDT 2013

* Joe Touch | 2013-04-25 11:46:38 [-0700]:
>Consider that ethernet ethertype 0x0800 was originally intended to
>mean "IP", allowing the IP version number to be determined at the IP
>layer, but packet demuxing efficiency concerns resulted in a new
>ethertype for IPv6 (0x86DD). So the ethertype includes not only the
>upper layer protocol, but it's redundant with the version at the next
>Similarly we could allocate a new ethertype to "IPv4:TCP" or "IPv4:SCTP".
>So any "mix and match" architecture needs to have some indication of
>what the particular mix is, but it need not be cascaded

In theory, but in practice this do not work because not every link is Ethernet
and you may end up re-parsing the packet to determine the transport protocol
at each hop.

Limit the ethertype to the next layer was fine. The redundant information in
Ethernet/IP header comes from the fact that we don't life in a perfect world
and things evolve over time.


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