Ethernet Problem, arpdump tool

[Dennis Bednar]

Its not clear to me how the the arpdump tool is to be used to aid
in tracking down ethernet communications problems.  There are
two cases I have in mind:

Case 1
Suppose that if you try to telnet to a host, it says "Trying ..."
but nothing happens, and suppose the last telnet/ftp happened a "long time ago".
Then what do you look for in the arpdump output
to give you a clue as to what the problem is?

Case 2
Supposed that you were in the middle of a telnet connection
to a remote host, and suddenly your
commands are no longer echoed, but the remote host is still up?

My question is this: can the ARP timer information in the
ARP table help you diagnose the problem?

I understand that the ARP timer is restarted (value set to 0 in
this implementation) when a packet is sent to a given IP address,
and that the ARP timer value (measured in minutes in this implementation)
gets to 20 (in this implementation),
most of the information in the slot is cleared (except
for the Ethernet Station address in this implementation). Therefore,
if the 2 hosts were not last communicating for over 20 minutes,
when an unsucessful telnet was tried (Case 1) you could now run
arpdump on both hosts.  Arpdump would show you that neither host has
the IP address of the other host in the tables (if it did, then
you would not suspect an ethernet problem, but rather a tcp or telnet
problem).  But for case 2,
is the ARP timer timer still restarted, even though the
packets are going into "thin air"?  I suppose it would be,
since IP is a datagram protocol, IP has no knowledge if the packet arrived,
and so my guess is that arpdump tool would not be so useful in
case 2.
-- 
Dennis Bednar	Computer Consoles Inc.	Reston VA	703-648-3300
{decvax,ihnp4,harpo,allegra}!seismo!rlgvax!dennis