Path: utzoo!utgpu!water!watmath!clyde!bellcore!rutgers!mit-eddie!uw-beaver!teknowledge-vaxc!sri-unix!hplabs!hpda!hpcuhb!hpindda!daver
From: daver@hpindda.HP.COM (Dave Richards)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: a proposed modification to ARP
Message-ID: <6200006@hpindda.HP.COM>
Date: 11 Jul 88 17:20:18 GMT
References: <8807092227.AA09479@hogg.cc.uoregon.edu>
Organization: HP Technical Networks, Cupertino, Calif.
Lines: 23

> Adding an additional HOST_DEAD state to the ARP tables could be used
> to handle these cases; ARPs for dead hosts would be limited to no more
> than one every minute or so.  A sophisticated algorithm would arp very
> frequently initially, but use a backoff to increase the delay between
> successive ARPs as the number of consecutive non-responses increases.
> This scheme also has the beneficial side effect of allowing IP to
> return ICMP host unreachables for dead machines.

I like this idea.  LAN traces of our local network have illustrated
that such a "state" is quite necessary.  NFS and TCP traffic for
down hosts generates sooo many ARPs, it's an nightmare.

> 4.3 BSD ARP times out unaccessed cache entries every 20 minutes.  Is
> there any good reason not to increase the value to several hours or
> longer?  Broadcasts are expensive and memory is cheap.

A number is just a number.  But...  20 minutes isn't that short a
time-period, with respect to most LANs.  Also, directed ARP requests
for cache entries being timeed-out, is one way of easing the burden on
the network, ehile sllowing the cache entry to die in a moderate period
of time.

	Dave Richards