Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!USNA.MIL!tcs
From: tcs@USNA.MIL (Terry Slattery)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  Dumb vs. smart host routing
Message-ID: <8805252319.aa17134@CAD.USNA.MIL>
Date: 26 May 88 03:19:45 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 21

> Second, the software should have the list of default gateways that I keep
> bringing up rather than just one.

The folks at BRL have done just that in some user mode software that
they cooked up during the times when RIP was still being developed.

They ping the list of gateways with a long time constant to get a
metric on which ones are up and what the error rate is to them.
(Remember, this is only done on the local network where the ping
loading is deemed necessary to support the dynamic reconfiguration.)
If the primary gateway goes down, the user mode process performs a
system call (Unix 4.2/3) to change the default route to one of the
secondary gateways.  The primary gateway is still pinged.  When it
comes back up (or the loss rate becomes acceptable), the pings are
increased in frequency to get a better indication of the link's
operation.  If everything still looks good, the kernel is told to
switch back to the primary gateway.

This type of dynamic routing could be put to good use in systems like
the Excelan VMS product.

	-tcs