Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!ucsd!ucbvax!BU-IT.BU.EDU!kwe From: kwe@BU-IT.BU.EDU Newsgroups: comp.protocols.tcp-ip Subject: Re: flooded with routing updates? Message-ID: <8807081659.AA04052@buit13> Date: 8 Jul 88 16:59:33 GMT Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 45 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