How do I change ARP proxy machines for the DiRT network?

4/3/02 : modified by Jay Aikat.

Note that the procedure for changing proxy arp machines remains the same, as described below. However, tyagi now proxy arps for 152.2 and skipper161 still proxy arps for 152.19, but the hardware has changed (from a 400MHz PII to a 200MHz pentium)

11/6/98 : created by David Ott
Here's a quick set of notes from when we changed the DiRT network ARP proxy machine from sam to yako137 on 11/6/98. (Later we changed yako137's name to sam and took the old sam offline.)

  1. We added the following bit of code to /etc/rc.local on yako137, and commented the same piece of code out in the same file on sam.
    # Load in the arp tables for proxy arp - BEGIN
    /sbin/ifconfig xl0 down
    /usr/sbin/arp -f /etc/arp.generic.table
    /usr/sbin/arp -f /etc/arp.topsecret.table
    /sbin/ifconfig xl0 up
    # Load in the arp tables for proxy arp - END
  2. We ftp-ed /etc/arp* files from sam and put them on yako137 in the same directory.
  3. We ran arpflush on sam to remove the ARP table currently loaded in memory.
  4. Rebooting yako137 to load the new ARP table would have worked, but a more graceful thing we did was to run arpflush and then the commands added to /etc/rc.local concatenated like this:
    /sbin/ifconfig xl0 down ; /usr/sbin/arp -f /etc/arp.generic.table ; /usr/sbin/arp -f /etc/arp.topsecret.table ; /sbin/ifconfig xl0 up
    You need to concatenate the commmands like this so that you don't lose your connection during the process.
  5. Finally, we tested that everything works by pinging each DiRT machine from a machine outside the DiRT network in the department.

Note that if the network card on topsecret ever changes in the future, the table files will need to be revised.

Also note that sam proxy arps for the 152.2 net and skipper161 proxy arps for the 152.19 net.

Date: Fri, 23 Jul 1999 14:42:29 -0400 (EDT)
From: David Ott 
Subject: skipper161

The old skipper ( has now been renamed to

        skipper161 (

The reason has to do with the proxy arp problem we've run into before.

Sam, which normally proxy arps for the experimental and test/development
networks, is unable to load 152.19.* entries in /etc/arp.goldberg.table
because of its IP address (152.2) and netmask (255.255).  That means we
can't get to 152.19.160 machines on the test/development networks from

To solve the problem, we have changed skipper to be a 152.19 machine
(which is still on the department network) and configured it to proxy arp
for the 152.19.160 block of test/development machines.  

Seems to work okay, but let me know of any problems.


David Ott 11/6/98