ARP / Cisco Router Wierdness

Stacey Roberts stacey at
Fri Jun 25 10:45:35 PDT 2004


----- Original Message -----
From: "Bill Moran <wmoran at>"
To: To Peter Pauly
Date: Fri, 25 Jun, 2004 15:21 BST
Subject: Re: ARP / Cisco Router Wierdness

> Peter Pauly <ppauly at> wrote:
> > This morning while attempting to replace a server with a new machine
> > (same IP address, the old machine was unplugged), The Cisco 2600
> > router's arp table continued to point to the old DNS server's MAC
> > address.
> > 
> > Even after rebooting the new server (Freebsd 5.2.1), the MAC address
> > remained unchanged in the router. The router continued to point to the
> > old machine's MAC address.
> > 
> > I updated the entry manually in the router and all was well. But I am
> > concerned that Freebsd is not announcing it's MAC address when the
> > machine or interface comes up. Any ideas?

Cisco routers (depending on IOS version) will cache arp entries for at least 20 mins. To force an update, simply run "clear arp" on the router and any Cisco IOS-based switches as well.



> I'm not an ARP expert, but isn't it the job of the device maintaining an
> ARP table to properly time out and refresh the entries in that table?
> I.e.  shouldn't you be posting this question to a Cisco mailing list,
> asking why the 2600 didn't automatically pick up the new MAC address?
> Corrections are welcome if I'm wrong on this count.
> -- 
> Bill Moran
> Potential Technologies
> _______________________________________________
> freebsd-questions at mailing list
> To unsubscribe, send any mail to "freebsd-questions-unsubscribe at"
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 466 bytes
Desc: not available
Url :

More information about the freebsd-questions mailing list