Path: utzoo!attcan!uunet!husc6!spdcc!kaos!romkey From: romkey@kaos.UUCP (John Romkey) Newsgroups: comp.protocols.tcp-ip Subject: Dumb vs. smart host routing Message-ID: <864@kaos.UUCP> Date: 12 May 88 01:01:00 GMT References: <8805102321.AA26819@hogg.cc.uoregon.edu> Reply-To: romkey@kaos.UUCP (John Romkey) Organization: Chaos; Somerville, MA Lines: 52 In article <8805102321.AA26819@hogg.cc.uoregon.edu> jqj@HOGG.CC.UOREGON.EDU writes: >>You REALLY DON'T want hosts to know about routing. >At issue here is a critical point: how smart is it desirable for hosts >to be? Braden argues that they should be very dumb. I would argue >that they can be dumb if they don't really need connectivity off their >network, but should be a little bit smarter if possible. As the network grows the part which will give out is the routing substrate. The Internet has already had this happen a few times. We went from GGP to EGP, then EGP broke and it had to support multiple packet updates, and now we're in the process of scrapping EGP for the next step. Each of these steps was good enough for networks of a certain size and broke as the network grew. If we can keep the hosts as stupid as possible with regard to the routing algorithms and bottle the complexity up in the routers then we're in a better position to deal with the next time the Internet hits a level where the existing routing protocols break. Whatever the next solution is, it may not hold for 10,000 networks. Or 100,000 networks. With one or two hundred hosts per network. [I've been working with TCP/IP long enough that when I started, we called routers 'gateways', so know that I'm using them as synonyms in this message.] I'd rather treat the network as a black box from the host's point of view. For a host with a single network interface, I think the best way for it to route is to have a list of default gateways which it cycles through, caching a route with a 'connection'. If TCP notices problems with lots of retransmissions, it could call IP and request that it reroute the connection (IP flushes the route and uses a different default gateway). Since the gateways know the TRUTH they can send ICMP redirects when they believe there is a better route. If some new protocols were cooked up to allow hosts to query routers for some useful information WITHOUT the hosts understanding how the routers worked, that would be okay as far as I'm concerned. Multihomed hosts are a more substantial problem, and right now they probably do have to at least listen to routing protocols in order to figure out the best routes to use. This way, the next time the routing substrate breaks because the Internetwork has grown too much, only the routing substrate needs to be changed. Just fixing this will be a bad enough problem without having to change all the host software in the world. We'll have a lot more flexibility to change the routing substrate then. -- - john romkey UUCP: romkey@kaos.uucp ARPA: romkey@xx.lcs.mit.edu ...harvard!spdcc!kaos!romkey Telephone: (617) 776-3121