From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.protocols.nfs,comp.dcom.isdn
Subject: Re: Low cost ether/isdn brouters (was PC-NFS PPP Serial/ISDN driver wanted)
Date: 21 Jan 93 17:10:02 GMT
Organization: Silicon Graphics, Inc.  Mountain View, CA

In article <1993Jan21.151029.13640@gandalf.ca>, dcarr@gandalf.ca (Dave Carr) writes:
> ...
> >Just 2x64k (uncompressed would be ok), with real router sw (SNMP, RIP, ARP,
> >OSI?) rather than a filtering bridge is what I want. However it can be
> >oriented to a very small net doing quite simple routing (i.e. its not due
> >to a vast LAN at my house, but the fact that I, may, want a different network
> >then the other end of the bridge, that makes me want a router rather than a
> >bridge).
> 
> Interesting.  Could you tell me more.  With ISDN, we are basically talking
> about a point-to-point link.  Our view is with the right software mods, you
> can get the desired performance out of a bridge.  The trickiest part is the
> handling of multicast and broadcast.  If we can eliminate these packets
> without doing the entire routing function, do we have what you need?


I've argued vigorously with Gandalf representatives about their
"brouter."  (Which word I hope they have removed from the brochure
describing their half-bridge!)  Their position was "<big company> told
us to build it like that, because no one at <big company> who would use
it has their own ethernet at home."  My response was that they hadn't
talked to the right people at <big company>, that while the I/S or MIS
people at <big company> night have only dumb terminals, the real users
are engineers with heaps of hardware at home.

Anyone who wants to run a dumb terminal over a network protocol over
ISDN (e.g. TCP/IP/ISDN) will probably not have an ethernet at home,
such a person either has other, unsual requirements or has more money
and technophilia than brains and should instead just use a $300 raw
modem (or ISDN) link.  This also applies to less dumb, X terminals,
which should be using one of the new light weight, serial line X
protocols instead of vanilla X/TCP/IP/ISDN.

Many who want to run network stuff over ISDN have real networks on both
sides of the point-to-point link.  This applies just as much to
companies who might replace leased lines in large "WAN's" with ISDN
links as it does to individuals.  Individuals may often have only 1 or
2 computers and a printer, but the reasons they have for treating their
local network as something other than a bridged extension of the
other network are similar.

If bridging were always the right answer for corporate WAN's, then none
of those point-to-point links would not be using routers.

If your argument were valid, "just fix the MAC group address bit
problems and then bridges are enough", then there would be no market
for routers.  If your argument were valid, then Cicso would not be in
business, and neither would Wellfleet.   Instead, there would only be
companies making clones of DEC bridges.


> SNMP management we have, ARP we will spoof, why RIP on point-to-point link,
> and OSI that deserves its own sentence.  We now have OSI, but there is
> little demand. 
>
> There isn't that much difference in performance between a bridge and a
> router in terms of forwarding performance.  The big difference is the
> 100's of Kbytes of code to support the various stacks. 
> ...

IP routing does not require "100's of KBbytes of code".  Just how big
is ka9q?


Maybe bridging is the right answer for Appletalk, OSI, and so on.  In
some cases, bridging may make sense for IP.  But bridges are not a
universal solution.

I won't rehash here the very old bridge-vs-router war.  Instead, you
should stop and think about why routers are still popular.

Consider one example.  Assume you are employeed by <big company> and
want to run ISDN to the corporate network to work at night.  Assume you
have only 1 PC running 386BSD on your ethernet.  What if you also want
to connect your machine a low cost Internet provider ($1/hour PPP or
SLIP) to participate in mailing lists or to get source that <big
company> might not appreciate?  Or maybe the firewall between the
corporate network at <big company> and the Internet is inconvenient or
too high for you.  If you have a real network and a real ISDN router,
you can route directly to the corporate network or to CERFNET or CSN at
will.  In this example if you have only a bridge, you have either a
white elephant or a set of shackles locking you to the company network.

Finally, I notice that you posted this to comp.protocols.nfs.  That
suggests you are thinking about running NFS over your ISDN boxes.  NFS
usually implies NIS.  NIS almost always involves broadcast packets.
How are you going to "eliminate these [broadcast] packets"?


Vernon Schryver,  vjs@sgi.com.