Re: Dumb vs. smart host routing


KASTEN@MITVMA.MIT.EDU
Fri, 13 May 88 10:10:16 EDT


> 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.

UNfortunately, not all of the systems that use IP are (easily) capable of
running a RIP listener. PC's are the best example - they do not have
multitasking, making it difficult to load in a program to listen to the
RIP traffic. There are ways of doing it but this is not a forum for
discussing PC stuff.

>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).

Not all of us are so lucky as to have a BSD system available on which
we can build our stuff.

I like the idea of the "I am a Router" broadcast's. The problem, again,
is that not all hosts may be capable of listening at all times for that
broadcast (even a BSD machine could be turned off). Instead, a query and
response type of protocol could be used. When a host needs to send
something off net and either A) does not have the IP Address of any
router (if it had one address, it could send a packet to that router
and get the redirect) or B) the host decides that the router it is
using is dead (e.g. TCP has retransmitted too often) then the host
broadcast a "Who can route to network X?" request and the routers on
the local network would respond. This would require changes to both
routers and hosts, but I think is the most flexible over the widest
range of hosts - from the single "tasked" PC's up to Crays. Of course,
you still can listen to RIP (but what if the routers want to use
another protocol?)

Frank Kastenholz



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