Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!uunet!telebit!brian
From: brian@telebit.com (Brian Lloyd)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Help designing address allocation in a metronet
Keywords: SLIP subnet
Message-ID: <1991Apr14.055343.16944@telebit.com>
Date: 14 Apr 91 05:53:43 GMT
References: <1991Mar20.150615.18929@m2xenix.psg.com>
Sender: news@telebit.com
Organization: Telebit Corporation; Sunnyvale, CA, USA
Lines: 28
Nntp-Posting-Host: napa.telebit.com


GAK!  You certainly can eat up a lot of address space using SLIP
links.  The problem is inherent in the "an IP address per interface"
and in the "everybody in a (sub)net must share the same (sub)net
number" concepts.

In spite of the fact that it violates tradition and the router
requirements RFC, we chose not to assign a unique IP address to each
interface in the Telebit NetBlazer dial-up router.  The SLIP or PPP
links do not need their own unique IP address and, in fact, all
interfaces are allowed to share the same IP address.  This GREATLY
reduces the number of (sub)nets required to build a network.

The trick that we use is to use an interface name in the routing table
rather than the gateway address to determine which interface to use.
We count on the fact that in a point-to-point SLIP or PPP connetion
there can be only one destination for a packet that is shoved into one
end of a link.  Therefore we really do not care what the IP address is
on either end of the link.  We trust that the remote peer will behave
in a router-like manner and forward the packet along the way toward
its ultimate destination.

Bottom line is that it works and doesn't eat up address space.
-- 
Brian Lloyd, WB6RQN                              Telebit Corporation
Network Systems Architect                        1315 Chesapeake Terrace 
brian@napa.telebit.com                           Sunnyvale, CA 94089-1100
voice (408) 745-3103                             FAX (408) 734-3333