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From: ks@pur-ee.UUCP (Kirk Smith)
Newsgroups: comp.dcom.lans
Subject: Re: routing table management (routed)
Message-ID: <5003@pur-ee.UUCP>
Date: Sun, 7-Dec-86 15:39:32 EST
Article-I.D.: pur-ee.5003
Posted: Sun Dec  7 15:39:32 1986
Date-Received: Mon, 8-Dec-86 03:29:14 EST
References: <675@arthur.cs.purdue.edu> <7541@topaz.RUTGERS.EDU>
Reply-To: ks@pur-ee.UUCP (Kirk Smith)
Distribution: na
Organization: Electrical Engineering Department , Purdue University
Lines: 49

In article <7541@topaz.RUTGERS.EDU> root@topaz.RUTGERS.EDU (Charles Hedrick) writes:
>Here are some other problems.  Note that these often are not
>significant for a network constructed entirely of Ethernets.  But for
>heterogenous networks, they are.  (Our network has links to the
>Arpanet, NSFnet, and one of our internal links is very slow.)
>  - routed uses hop counts.  This is only a good idea if all of
>	the links are roughly the same speed.

In 4.3 BSD, a per-interface metric can be set to increase the "hop count"
for slow interfaces.  This feature can be used when a high speed and a low
speed link are available.  Under normal operation, the high speed link would
be used.  When it is unavailable, the low speed link would be used.

>  - it has no way to help coordinate load sharing among parallel
>	routes of comparable goodness

True.  This would only be a problem, though, if the parallel routes were
both "low" speed.  A single "high" speed route is enough to support typical
network traffic, without sharing with another "high" speed route.

>  - it has no way to specify default gateways.  If you have a
>	"generally competent" exterior gateway, e.g. an Arpanet
>	gateway, you may not want to propagate
>	the whole list of networks accessible from the Arpanet
>	through your routed setup.  Sites with more than one
>	Arpanet gateway are more likely to want their internal
>	routing protocol just to find them the "nearest" Arpanet
>	gateway.

If a routed is started with the "-g" flag, that machine is assumed
to be an "external" gateway.  It will advertise a default route.
If you have multiple arpanet gateways, that is no problem.  Routed
will pick the "nearest" OPERATIONAL Arpanet gateway.


I am not trying to promote routed as the perfect solution to all problems,
but it seems to work quite well for us.  Many of the perceived problems with
routed are just not true.  Other solutions, such as Proxy ARP and route
redirects, are not as complete as routed.  Gateways going down are real
problems that need to be dealt with.  If we used routing algorithms that
could not find a route when one exists, our users would be quite upset.
On the other hand, routed has not been implemented by all machines that
run TCP/IP.  But there is no reason that it couldn't be implemented.
And it certainly does not preclude those machines from running on the
same internet, with less than optimal routing capabilities.  At this time,
there seems to be no serious alternative for us.

					Kirk Smith
					Purdue Engineering