On Sun, Jun 17, 2018 at 10:36:10AM -0400, Noel Chiappa wrote: 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). 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. DF