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From: gds@sri-spam.istc.sri.com (The lost Bostonian)
Newsgroups: comp.dcom.lans
Subject: Re: Milking machine performance/function (routing table management)
Message-ID: <9764@sri-spam.istc.sri.com>
Date: Sat, 6-Dec-86 15:31:55 EST
Article-I.D.: sri-spam.9764
Posted: Sat Dec  6 15:31:55 1986
Date-Received: Sun, 7-Dec-86 03:44:54 EST
References: <675@arthur.cs.purdue.edu>
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In article <675@arthur.cs.purdue.edu>, narten@arthur.cs.purdue.edu (Thomas Narten) writes:
> I would have to dispute what you call as "most common". Routing redirects
> and proxy ARPs are one way to manage routes, but all is not rosey. With
> redirects, one starts with one gateway finds new and better routes cause the
> gateway you are currently using tells you of a more direct path. If that new
> route should go away, however, you have no way of finding out cause you
> would need a redirect from the gateway that just went away. You may in fact
> have another gateway that could still be used. RIP would detect gateways
> that go away and either remove the route or find another gateway. In
> summary, Redirects can be used to fix up incorrect entries, not to manage
> routing tables. It certainly has as many and probably more problems than
> RIP. 

The BBN 4.2 TCP/IP implementation pings the gateway listed in the
routing tables periodically.  When the gateway is marked "down" because
it does not answer its ping in m out of n tries (I forget the exact
numbers) the connection is retried using the "default" gateway.  This
will cause another round of redirects to be sent, until the original
route is good, or another path through the internet is found.  When a
gateway crashes which is the only gateway onto a network, communications
with that network are cut off until the gateway comes back up, but a
flurry of redirects is sent nevertheless.  There is a problem with too
much pinging contributing to network congestion, but this can be
alleviated by implementing pinging with exponential backoff.

4.3 BSD TCP/IP does not do any pinging.
 
> 4.3 BSD will issue and accept redirects if properly configured. Properly
> configured means that it must have 2 or more "real" interfaces (loopback
> doesn't count), otherwise it thinks it is a host. This is a wise decision,
> as hosts aren't gateways, and shouldn't act as such. 4.3 will change routing
> entries that are updated via redirects. It will, however, only do so if the
> redirect came from the same gateway it is currently routing packets
> addressed to the destination given in the redirect to. This prevents it from
> installing redirects that come from a random host. 

4.2 BBN TCP/IP would not enter a new route from a redirect into its
tables unless it came from a gateway which was already in its tables.

--gregbo