[TUHS] core

Derek Fawcus dfawcus+lists-tuhs at employees.org
Mon Jun 18 01:58:52 AEST 2018

On Sun, Jun 17, 2018 at 10:36:10AM -0400, Noel Chiappa wrote:
>     > From: Derek Fawcus
>     > Are you able to point to any document which still describes that
>     > variable length scheme? I see that IEN 28 defines a variable length
>     > scheme (using version 2)
> That's the one; Version 2 of IP, but it was for Version 3 of TCP (described
> here: IEN-21, Cerf, "TCP 3 Specification", Jan-78 ).

Ah - thanks.

So my scan of it suggests that only the host part of the address which were
extensible, but then I guess the CIDR scheme could have eventually been applied
to that portion.

The other thing obviously missing in the IEN 28 version is the TTL (which
appeared by IEN 41).

>     > and that IEN 41 defines a different variable length scheme, but is
>     > proposing to use version 4.
> Right, that's a draft only (no code ever written for it), from just before the
> meeting that substituted 32-bit addresses.
>     > (IEN 44 looks a lot like the current IPv4).
> Because it _is_ the current IPv4 (well, modulo the class A/B/C addressing
> stuff). :-)

I wrote 'a lot', because it has the DF flag in the TOS field, and an OP bit
in the flags field; the CIDR vs A/B/C stuff didn't really change the rest.
But yeah - essentially what we still use now. Now 40 years and still going.

The other bit I find amusing are the various movements of the port numbers,
obviously they were originally part of the combined header (e.g. IEN 26),
then the IEN 21 TCP has them in the middle of its header, by IEN 44 it is
sort of its own header split from the TCP header which now omits ports.

Eventually they end up in the current location, as part of the start of the
TCP header (and UDP, etc), essentially combining that 'Port Header' with
whatever transport follows.


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