Re: a proposed modification to ARP


Dave Richards (hpda!hpcuhb!hpindda!daver@ucbvax.Berkeley.EDU)
11 Jul 88 17:20:18 GMT


> 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



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