SUMMARY: Arp Table Problems

From: Charlie Dennett (dennett@Kodak.COM)
Date: Fri Jan 17 1992 - 00:26:17 CST

Thanks for the replies. As you pointed out, the problem I saw in the
output of arp -a is probably not the cause of my automounts and rsh
commands failing. My guess is that both the arp problems and the
other problems are the results of some other problem. It's just that
every thing was going along fine and then suddenly broke. I checked
that I could connect to the name server via nslookup, checked the
NIS host tables, checked the routing tables and the arp tables. The
only thing that looked out of place was the arp tables. BTW, the name
server is in another building and out of my control. Rlogin and
telnet worked to hosts that did not appear in my host table but did
appear in the name server.

Someone said that arp uses gethostbyaddr. Further experiments showed
that once the output of arp -a printed a question mark in place of a
hostname, all subsequent host names were replaced with question marks.
If I manually deleted the first such entry, the following entries
suddenly had real hostnames associated with them (until it came to another
hostname that had a question mark. Then all the ones following that
were question marks.) In each case the first entry that had a question
mark in place of a host name, the host did not appear in my NIS host
table but did appear in the nameserver (verified via nslookup).

It would appear that perhaps the gethostbyaddr routine is buggy or perhaps
the arp program is buggy or perhaps the nameserver is buggy. I'll
have to see what I can do to isolate it to one of these if I can.
Maybe someone has been messing around with the dynamic libraries that
I am unaware of. Oh yes, I did rebuild the entire suite of NIS maps.

Another strange thing is that this happened on two systems separate
by severalmiles geographically and who knows how many router, bridges
and other hardware. The only thing they have in common is they both
consult the same name server. Someone locally suggested that perhaps
a new piece of hardware was put on the network and was misconfigured.
It could be sending some sort of packet that is messing up something.

Oh well, thanks again. If I ever find out what happened, I'll let you
all know. Meanwhile, if you think of something, please let me know.

Charlie Dennett dennett@Kodak.COM

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