Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!decwrl!sgi!vjs@rhyolite.wpd.sgi.com
From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.dcom.lans
Subject: Re: FDDI question: bridges, routers, interoperability ...
Summary: should work
Keywords: FDDI, bridges, routers
Message-ID: <106313@sgi.sgi.com>
Date: 27 May 91 18:44:07 GMT
References: <1779@ariadne.csi.forth.GR> <22755@shlump.lkg.dec.com> <1793@ariadne.csi.forth.GR>
Sender: guest@sgi.sgi.com
Distribution: comp
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 26

In article <1793@ariadne.csi.forth.GR>, nicolas@csi.forth.gr (Nicolas Chrissakis) writes:
> 
> Anyone out there has installed FDDI bridges and FDDI routers (acting as 
> routers only) and made them inoperate?

Anyone who has found that such a combination does not work should get their
money back.  Any IP (as in TCP/IP, UDP/IP, or any-other/IP) router looks
like a normal IP host to a bridge.  Any "translating" or "translucent"
bridge is invisible to any pair of IP hosts it connects.  By definition the
IP host on the FDDI ring cannot tell the other IP host is not also on the
ring, and the ethernet IP host cannot tell that the other IP host is not
also on the ethernet.

I say again that there are rumors some bridge customers have found some
bridges are not sufficently transparent.  One brand is said to be unable to
keep up while bridging the 4KByte NFS/UDP/IP packets generated by a brand
of computer that I care about.  Those of us who care about speed use up to
the 4352 byte FDDI MTU defined in RFC-1188 and the familiar IP rules of
local MTU for traffic on the LAN and 576 bytes other times.  This requires
FDDI-ether bridges to do IP-fragmenting.  The possibly slow bridge vendor
has not been named in this forum recently.  I know no rumors about the
performance of the bridges recently mentioned by name here, other than the
statement of a very knowledgable employee that they run at media speed.

Vernon Schryver,   vjs@sgi.com
Disclaimer:  I'm of the router religion instead of the bridge faith.