SUMMARY Making ARP entry permanent

From: Bill Fenwick (
Date: Mon Nov 06 2000 - 14:12:18 CST

Original question:

>This one's probably embarrassingly simple, but for the life of me, I can't
>figure it out and can't find the answer in the archives or other docs I've
>We've got six servers, three running Solaris 2.6 5/98, two running Solaris
>7 8/99, and one running Solaris 7 11/99. We recently changed ISP's, which
>also meant we had to install a new router/firewall machine, which we did.
>Here's the problem. In order to get our servers to recognize the new
>router and use it as the default, I added it to the ARP tables with arp
>(As I recall, I had to do this with the old router to get it to work
>right). Our servers are rebooted every weekend, and on two of the 2.6
>machines, everything is fine, they find the router with no problem. On
>other four machines, the ARP entry still has the S (static) flag on it and
>disappears on reboot, so that those machines can't find their default
>router. So I have to do arp -s all over again and then add the default
>route manually (with route add).
>Of course, I can't remember what I did to make the arp entry permanent on
>the two machines that do work... probably dumb luck, whatever it was.

Well, I was right... it was embarrassingly simple.

Thanks to the following for responding:

Brian Hostetler <>
Thomas Lewis <>
Alan Reichert <>
Richard Sullivan <>
Dan Brown <>
Timothy Lorenc <>
Sean Quaint <>
L. Bryan Moore <>
Ericka Fowler <>
Changa Anderson <>
Doug Winter <>
David B. Harrington <>

Most suggested I add the /etc/defaultrouter file and put the IP address or
name of the router in it. Forgot to mention that I did that already. That
gives the default router to add using "route add default"... my problem was
that the ARP entry for the router wasn't being found (since it was a
static, rather than learned, entry, it was being deleted on reboot) so the
default router wasn't being added.

A couple people suggested I put the "arp -s" command in a startup script,
but Dan Brown hit the nail on the head when he reminded me that:

>You shouldn't have to mess with the arp tables, save maybe to flush
>them to get them to see the router the first time around -- even then, the
>Arp cache should time out in about 5 minutes, and then get updated as
>needed, automatically.

There was no need for me to add the router's Ethernet address to arp
manually. I removed the entry I had added, left the router as the default,
did a ping to somewhere outside our network, and presto -- the arp entry
was added automatically and was "learned", not static. Problem solved.

Thanks again to all.

Bill Fenwick                               Email:
Digicomp Research                          Voice:  (607) 273-5900 ext 32

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