Re: Dumb vs. smart host routing


John Romkey (ROMKEY@XX.LCS.MIT.EDU)
Thu 12 May 88 14:38:09-EDT


>One problem with it is that it doesn't work if the local network is
>extremely dynamic, with lots of routers coming and going.

I envision networks where links to other networks come and go, but not the
actual routers themselves. It's a strange idea to me. I don't see any
application for it off the top of my head.

>An "ad absurdum" extension to your argument is that a host shouldn't have to
>have ARP;

No, I think there's a big difference between the two examples. I don't want
the hosts to have complete lists of all the routers on their network. Just
a list of a few - the default routers. Many systems nowadays have an idea
of one default router; I'd like to increase it to an arbitrary list of them
which is cycled through for reliability. If you have only one default router
then you lose big when it goes down. Since the routers all talk to one
another, they know the best routes and if the default router chosen for
a particular connection isn't the best, it will send an ICMP redirect and
the host should change its route.

It occurs to me that we're agreeing to some extent, but arguing over details.
I don't care too much how the host discovers what its default routers are.
Could be statically configured (though this isn't too good), BOOTP or
some new broadcast ICMP message.

I think that the details that we're disagreeing over are:

1. How many routers the host knows about. I want it to only have to know about
        a few. I don't really care how many, I'd like it to be more than one.
        At least nothing should depend on it knowing about them all.
        It doesn't bother me if the host does or doesn't know them all;
        ICMP will clean up the mess.

        I'm not sure that we're really disagreeing over this one...

2. How it discovers them. I'm very opposed to the host discovering routes
        by using routing protocols that the routers use internally. Having
        part of the routers' protocol be an interface to hosts which says
        "I'm a default router" or "This is a list of default routers for this
        subnet" is okay, as long as the host implementations don't sticky
        their fingers by prying open the routing protocols any more than that.

        If there's some way to do it without a broadcast protocol, or with
        one that minimizes the number of broadcasts, that would be a good
        thing.
                                - john
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