SUMMARY Making ARP entry permanent

From: Bill Fenwick (bill@digicomp.com)
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
>seen.
>
>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
-s.
>(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
the
>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 <brian@adenine.sinebubble.com>
Thomas Lewis <tlewis@u-data.com>
Alan Reichert <aareichert@tasc.com>
Richard Sullivan <RSullivan@espeed.com>
Dan Brown <brown@obscure.org>
Timothy Lorenc <tim@load.com>
Sean Quaint <squaint@mediaone.net>
L. Bryan Moore <LBMoore@scrippsweb.com>
Ericka Fowler <Ericka.Fowler@central.sun.com>
Changa Anderson <canderson@sitesmith.com>
Doug Winter <dwinter@businesseurope.com>
David B. Harrington <dharringt@deq.state.va.us>
<hmnguyen@verizongni.com>

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:  fenwick@digicomp.com
Digicomp Research                          Voice:  (607) 273-5900 ext 32

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