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1994-11-13
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Date: Sat, 15 Oct 94 04:30:01 PDT
From: Advanced Amateur Radio Networking Group <tcp-group@ucsd.edu>
Errors-To: TCP-Group-Errors@UCSD.Edu
Reply-To: TCP-Group@UCSD.Edu
Precedence: List
Subject: TCP-Group Digest V94 #230
To: tcp-group-digest
TCP-Group Digest Sat, 15 Oct 94 Volume 94 : Issue 230
Today's Topics:
ARP grumbles (3 msgs)
Unsubscirbe
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Archives of past issues of the TCP-Group Digest are available
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We trust that readers are intelligent enough to realize that all text
herein consists of personal comments and does not represent the official
policies or positions of any party. Your mileage may vary. So there.
----------------------------------------------------------------------
Date: Fri, 14 Oct 1994 09:34:42 -0800 (PDT)
From: jmorriso@bogomips.ee.ubc.ca (John Paul Morrison)
Subject: ARP grumbles
Why doesn't the ARP cache code in JNOS (1.08):
1. learn the hardware address from incoming packets. it's pretty
silly to receive an incoming packet (say an ICMP echo request) then
turn around and broadcast an ARP request when the hardware address
is right under its nose
2. why doesn't it reset the ARP cache timers when there are incoming
packets, instead of letting the timers run down, and have to
retransmit an ARP request. In other words, JNOS can hear a packet
a few ticks before the ARP timer runs down, but it doesn't reset the
timer, so it's forced to do a useless ARP request.
Life's bad enough at 1200bps, I'm going to add static ARP entries for
the important hosts.
---------------------------------------------------------------------------
BogoMIPS Research Labs -- bogosity research & simulation -- VE7JPM --
jmorriso@bogomips.ee.ubc.ca ve7jpm@ve7jpm.ampr.org jmorriso@ve7ubc.ampr.org
---------------------------------------------------------------------------
------------------------------
Date: Fri, 14 Oct 1994 16:30:53 -0400
From: "Louis A. Mamakos" <louie@alter.net>
Subject: ARP grumbles
> Why doesn't the ARP cache code in JNOS (1.08):
>
> 1. learn the hardware address from incoming packets. it's pretty
> silly to receive an incoming packet (say an ICMP echo request) then
> turn around and broadcast an ARP request when the hardware address
> is right under its nose
Because you don't know if the packet arrived from the source address
in the packet or not. It may be been forwarded from an intermediate
router.
> 2. why doesn't it reset the ARP cache timers when there are incoming
> packets, instead of letting the timers run down, and have to
> retransmit an ARP request. In other words, JNOS can hear a packet
> a few ticks before the ARP timer runs down, but it doesn't reset the
> timer, so it's forced to do a useless ARP request.
For the same reason above. You don't know what arp entry it's associated
with, especially if you play proxy ARP games. ARP caches are not usually
designed to be searched in that direction, either.
> Life's bad enough at 1200bps, I'm going to add static ARP entries for
> the important hosts.
Oh well. You could us a V.32bis modem on a dial-up connection and get
better throughput until we get better radios and modems.
louie
wa3ymh
------------------------------
Date: Fri, 14 Oct 1994 11:45:18 -1000 (HST)
From: Antonio Querubin <tony@mpg.phys.hawaii.edu>
Subject: ARP grumbles
On Fri, 14 Oct 1994, John Paul Morrison wrote:
> Why doesn't the ARP cache code in JNOS (1.08):
>
> 1. learn the hardware address from incoming packets. it's pretty
> silly to receive an incoming packet (say an ICMP echo request) then
> turn around and broadcast an ARP request when the hardware address
> is right under its nose
There is a limited 'arp eavesdrop' feature in the latest versions of JNOS.
But to blindly map every incoming IP address to an ARP entry isn't wise.
Suppose you were the only host on a net talking to a single default
router. Now suppose you had several dozen other hosts connecting to you
all through that router. Do you create several dozen ARP entries? At
what point does the IP routing table became useless and NOS becomes a
bridge rather than a router? Suppose instead of several dozen hosts
connecting to you it was several thousand over a period of days or weeks?
> 2. why doesn't it reset the ARP cache timers when there are incoming
> packets, instead of letting the timers run down, and have to
> retransmit an ARP request. In other words, JNOS can hear a packet
> a few ticks before the ARP timer runs down, but it doesn't reset the
> timer, so it's forced to do a useless ARP request.
The 'arp eavesdrop' feature does this for you. But remember that it
depends on arp responses heard on the net to reset timers.
Antonio Querubin
tony@mpg.phys.hawaii.edu / ah6bw@uhm.ampr.org
------------------------------
Date: Fri, 14 Oct 1994 19:36:00 -0400 (EDT)
From: Admin <uunet!k4ngc!root>
Subject: Unsubscirbe
unscribe
------------------------------
End of TCP-Group Digest V94 #230
******************************