IP address classes vs CIDR (was Re: Reviving ARPAnet)

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Jan 18 12:54:47 CST 2018

    > From: Eric Smith

    > which would respond to ARP requests for non-local addresses and reply
    > with the router's MAC address (on that interface), specifically in
    > order to make classful-only hosts work on a CIDR network.

Yeah, Proxy ARP (an early RFC here:


but IIRC it was people at CMU who first came up with the idea; this RFC is
from people at UT-Austin, documenting it) was originally done to support
subnetting (see


for more) when it was first introduced - for hosts for which people didn't
have the source, but needed to attach it to a subnetted network.

Subnetting was a stage before CIDR (which took subnetting and Carl-Herbert
Rokitansky's 'supernetting' and mushed them together).


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