Re: flooded with routing updates?


kwe@bu-it.BU.EDU
Fri, 8 Jul 88 12:59:33 EDT


        From braden@venera.isi.edu Fri Jul 8 12:35:55 1988
        [I said:]
                One way to get lots of routes showing up in a
                host is to be on an Ethernet with several gateways
                that are connected to different regional or backbone
                networks. If you want to do robust routing, your host
                needs a route to each reachable net and that number is
                getting pretty large today.

        [Bob said:]
        This is not a requirement for "robust routing." An Internet
        host should only need to know a few default gateways, and take
        Redirects to find out about the others. This is just another
        example why hosts wiretapping gateway IGP's is not a part of
        the Internet architecture, and is often a bad idea.

        Bob Braden

Sorry. I should have said [meant to say] "If you want to do robust
routing, your local router(s) need a route to each reachable net and
that number is getting pretty large [450 nets]." We have a local
backbone and the router that talks to the external gateways really
needs to hear about all the nets that each external gateway knows
about. It would be nice if it could find out reasonable metrics from
the external gateways, but that's a research topic. For now, we
kludge configured metrics to get from egp to local and from jvnc
ciscoIGRP to local and thereby make decisions on a gateway basis
instead of a network basis.

        Of course, only one of our local backbone routers really needs
all the info. All the other local routers can default to this local
authoritative router and the authoritative router can keep track of
450 nets split between the arpa-net and the regional-net. We have a
strictly hierarchical backbone, so a default works nicely. Now the
authoritative router defaults to arpanet but takes all the jvncnet
routes it can get.

        I have a problem with the statement "host should only need to
know *a few* default gateways". How does a host learn about more than
one default gateway? How does a host dynamically learn anything about
routers without participating in the gateway protocol?? [I know the
answer "ES-IS protocol". I mean today. now.]

        Kent England, Boston University



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