[TUHS] Early Internet work (Was: History of select(2))
jnc at mercury.lcs.mit.edu
Tue Jan 17 01:17:45 AEST 2017
> From: Tony Finch
This is getting a bit far afield from Unix, so my apologies to the list for
that. But to avoid dumping it in the Internet-History list abruptly, let me
answer here _briefly_ (believe it or not, the below _is_ brief).
> AIUI there were two major revisions to the IPv4 addressing architecture:
Not quite (see below). First, one needs to understand that there are two
different timelines for changes to addressing: in the hosts, and in the
routers (called 'gateways' originally). To start with, they were tied
together, but as of RFC-1122, they were formally separated: hosts no longer
fully understood the syntax/semantics of addresses, just (mostly) treated them
as opaque 32-bit quantities.
> subnetting (RFC 917, October 1994 ... RFC 950, August 1985), and
> classless routing (RFC 1519, September 1993)
Originally, network numbers were 8 bits, and the 'rest' (local) part was 24.
Mapping from IP addresses to physical network addresses was some with direct
mapping - ARP did not exist - the actual local address (e.g. IMP/Port) was
contained in the 'rest' field - each network had a document which specified
the mapping. (Which is part of the interoperability issue with old
As some point early on, it was realized that 8 bits of network number were not
enough, and the awful A/B/C kludge was added (it was dropped on the community,
not discussed before-hand). Subnetting was indeed the next change. Then the
host/router split happened.
Classless routing (which effectively extended addesses, for path-computation
purposes, to 32+N bits - since you couldn't look at a 32-bit IP address and
immediately tell which was the 'network' part any more, you _had_ to have the
mask as well, to tell you how many bits of any given address were the network
number) was more of a process than a single change - the inter-AS routing
(BGP) had to change, but so did IGP's (OSPF, IS-IS), etc, etc.
> originally called supernetting (RFC 1338, June 1992).
There was this effort called ROAD which produced RFC-1338 and 1519, and IIRC
there was an intermediate, involving blocks of network numbers (1338), and
that slowly evolved into arbitrary blocks (1519).
One should also note that the term "super-netting" comes from a proposal by
Carl-Hubert ("Roki") Rokitansky which did not, alas, make it to RFC. (His
purpose was different, but it used the same mechanism.) Alas, the authors of
1338/1519 failed to properly acknowledge his earlier work.
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