Re: workstation != gateway


J. Noel Chiappa (JNC@XX.LCS.MIT.EDU)
Fri 21 Feb 86 19:15:46-EST


        Right. There isn't a spec for exactly what a gateway has to
do; if there was such a spec it would need massive updating, since the
job of the gateways is continually changing. The IP Engineering Group
is exploring some pretty substantial changes to gateways, which will
make tracking the gateway functions even more difficult.
        My recommendation has for quite some time been that hosts and
gateways are very different, and that we should provide a 'specification
for a host IP layer' that will insulate hosts from changes in the
switches. It's not easy to make a host into a gateway, as the Berkeley
people found to their (and our) cost. Worse yet, the Engineering group
is stuck with either having its options limited by backward compatabilty
with unsuitable designs (as is the case with RIP [routed] and EGP).
        People building host IP layers should eschew adding 'simple
gateway functionality'; it's not simple. If you do, you'll be stuck with
something that a) doesn't work right, and b) will break even if it works
OK now, as the architecture changes. I like to make the analogy with the
electric power grid; it's easy to build an appliance you can plug in
that uses power (equivalnte of host); it's a much trickeier job to build
a generator you can plug into the system to support it (gateway).
        Too many people say "Oh, I already have a PDP11 (VAX, Sun, PC,
RT, etc); I'll just add another interface board and whip up a little
code." It's not that simple; 'nothing in networks is ever as simple as
it seems'. As the system grows, and we add mechanisms to deal with the
problem we are now seeing (e.g. the massive congestion, etc) it will just
get more complicated. 'There's no such thing as a free lunch.' Believe
it.

        Noel
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