Path: utzoo!utgpu!water!watmath!clyde!ima!spdcc!kaos!romkey From: romkey@kaos.UUCP (John Romkey) Newsgroups: comp.protocols.tcp-ip Subject: Re: Dumb vs. smart host routing Message-ID: <874@kaos.UUCP> Date: 13 May 88 06:22:54 GMT References: <8805102321.AA26819@hogg.cc.uoregon.edu> <864@kaos.UUCP> <10285@ulysses.homer.nj.att.com> Reply-To: romkey@kaos.UUCP (John Romkey) Organization: Chaos; Somerville, MA Lines: 48 In article <10285@ulysses.homer.nj.att.com> smb@ulysses.homer.nj.att.com (Steven Bellovin) writes: >One problem I see is that ICMP Redirect is largely useless. It's only >useful for the first gateway along the way to tell the originating host >to use a different gateway; it can't be used to tell an intermediate >gateway what the proper next hop is. But that's not really a problem with ICMP redirects at all. Look at it this way: ICMP redirects are the (okay, *a*) way routers communicate routing information to hosts XYZ (fill in your favorite routing protocol(s)) is the way routers communicate routing information to one another. If the routers are doing their job properly then the routers on the same subnet as the host will redirect it to the proper router via ICMP; this router will then do XYZ things to figure out how to route the packet from there. It's because of XYZ that the routers know when to redirect in the first place. >The conclusion of all this is that local gateways must be extremely >smart. The current scheme, with EGP, works well enough in the current >environment, where there's one central net (ARPANET+MILNET); it would >fail miserably if there were a large number of interconnected backbone >nets. > >I'm not certain what to do about the problem. The example assumes that the routers are screwed up in the first place. You don't necessarily have to have an incredible amount of information in your routers that are used by your host - you just have to have routing protocols that do the right thing (which may actually require incredible amounts of information...oh well). The thing to do about it is to refine the XYZ protocols (ancient GGP, RIP, EGP) so that they work better for larger, more complicated networks. Yes, the current system doesn't deal with complicated networks very well. It doesn't handle redundant routes well. It doesn't handle load-sharing very well. It doesn't route on Type of Service very well (because not a lot of routers support it and virtually no hosts set the TOS field in the IP header). I believe there are people on an IETF task force or working group or some such working on this problem. -- - john romkey UUCP: romkey@kaos.uucp ARPA: romkey@xx.lcs.mit.edu ...harvard!spdcc!kaos!romkey Telephone: (617) 776-3121