jon@CS.UCL.AC.UK.UUCP (03/31/87)
/* Written 8:22 am Mar 31, 1987 by kincl%hplnmk@com.hp.hplabs in pyr1:tcp-ip */ /* ---------- "Re: Response to anti-bridge comment" ---------- */ Received: from ucl-cs-nss by pyr1.Cs.Ucl.AC.UK with SMTP id aa05565; 31 Mar 87 8:21 WET Received: from sri-nic.arpa by mv1.Cs.Ucl.AC.UK via Satnet with SMTP id aa05190; 31 Mar 87 8:20 WET Received: from hplabs.HP.COM by SRI-NIC.ARPA with TCP; Mon 30 Mar 87 10:27:05-PST Received: from hplms1 by hplabs.HP.COM with TCP ; Mon, 30 Mar 87 10:25:06 pst Received: from hplnmk (hplnmk) by hplms1; Mon, 30 Mar 87 10:24:38 pst Return-Path: <kincl@hplnmk> Received: from hplnmk.hpl.hp.com by hplnmk ; Mon, 30 Mar 87 10:29:16 pst Message-Id: <8703301829.AA06404@hplnmk> To: "Phil R. Karn" <karn@com.bellcore.flash> Cc: tcp-ip@arpa.sri-nic Subject: Re: Response to anti-bridge comments In-Reply-To: Your message of Thu, 26 Mar 87 15:20:26 -0500. <8703262020.AA27749@flash.bellcore.com> Date: Mon, 30 Mar 87 10:29:13 PST Question: How well would all this work if you decided that you need redundant routes or if you decided that you do not want a start topology but have an arbitrary topology? Can you have a configuration like the following: ---------------Ethernet----------------- | | | | Bridge Bridge | | | | ---------------Ethernet----------------- | | | | Bridge Bridge | | | | ---------------Ethernet----------------- Yes, but. At UCL we run a mini internet with 5 sites interconnected by Megastream (thats 2.Mbps not T1) lines. We also run a lot of LAN technology, mostly ethernet. We reckon that it's swings and roundabouts whether we use MAC Bridges or Network Level relays (to use ISO jargon). TYhere is an emerging (ISO!) standard for MAC bridges, and the only thing it is waiting on is how to do loop resolution and access control (ie the things most people think are network level things, but ISO are beginning to concede are different in a LAN/MAN context). Anyway, its down to 1. performance 2. functionality a) traffic control b) Fault Isolation c) routing/loop resolution d) access control e) management of all this. There's absolutely no reason to get layerist about this. if the addressing and protocols can stand it, there's nothing to choose between MAC bridges and network lewvel relays if they happen to do the same job as well. broadcast/multicast limiting can be done if you use distributed nameservers (and arp klugery is not a hack, it can be managed properly as a ditributed multicast system in MAC bridges if you implement it). two asides: 1. MAC bridges also buy you more trustworthy access control, since it's harder to spoof physical address without being spotted than to spoof IP/network level address, specially if you dont buy the wrong LAN. 2. MAC bridges usually perform, better - eg NFS works through them - you have to kludge the silly numbers in the mount table to get it to go even through a cisco box - one of the better IP gateways around. We use network level relays (IP gateways) between sites over the megastream, and predominantly MAC bridges within sites. The choice seems to have made sense in terms of managing the system, but I suspect that we just got good hardware and software, and that's what counts in the end.