Re: Dumb vs. smart host routing


jqj@hogg.cc.uoregon.edu
Thu, 12 May 88 09:56:52 PDT


John,

  I sympathize, and agree that yours is a defendable position. One
problem with it is that it doesn't work if the local network is
extremely dynamic, with lots of routers coming and going. An "ad
absurdum" extension to your argument is that a host shouldn't have to
have ARP; it should be able to make do with some static tables -- of
course, that would be ridiculous since the list of hosts on the local
network is much too dynamic to make such a table reasonable (though
note that some implementations, e.g. SunOS 3.x diskless bootstrap,
required just such a table).

  Similarly, I claim that we will need some sort of discovery mechanism
if the list of gateways on a local network is expected to be large and
dynamic. We have such a discovery mechanism in place today; passive
RIP. I'm not recommending that we improve it, or that hosts use it for
anything except finding the first gateway.

  Note that if in fact most host implementations already supported a
list of default gateways then I'd be willing to live with that as an
alternative. Unfortunately, they don't; most implementations give you
exactly ONE default, which is not enough when that gateway crashes and
stops sending ICMP redirects.

>fixing this will be a bad enough problem without having to change all
>the host software in the world
I believe that a gateway can be taught to send out RIP packets saying
"I'm a default router" without sending out any other data. If so, this
would provide my desired discovery mechanism with no changes to a
common flavor of host software (i.e. BSD derivatives).



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