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Date:      Tue, 17 Sep 2002 15:30:14 -0700
From:      "Crist J. Clark" <crist.clark@attbi.com>
To:        Chris Byrnes <chris__byrnes@hotmail.com>
Cc:        questions@FreeBSD.ORG
Subject:   Re: arplookup xx.xxx.xx.xxx failed: host is not on local network
Message-ID:  <20020917223014.GB3323@blossom.cjclark.org>
In-Reply-To: <F738a3s875qIOjsnK7L0001ad5a@hotmail.com>
References:  <F738a3s875qIOjsnK7L0001ad5a@hotmail.com>

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[Inappropriate cross-post to -stable removed.]

On Sun, Sep 15, 2002 at 02:08:51PM -0500, Chris Byrnes wrote:
> My /var/log/messages is being filled, non-stop, by these errors looped:
> 
> Sep 15 13:41:28 servername /kernel: arplookup xx.xxx.xx.xxx failed: host is 
> not on local network
> Sep 15 13:41:28 servername /kernel: arplookup xx.xxx.xx.xxx failed: host is 
> not on local network
> 
> After doing some reading, I've already issued, "sysctl -w 
> net.link.ether.inet.log_arp_wrong_iface=0" thinking that would fix the 
> problem.  Unfortunately, it has not.
> 
> Any ideas?

This is a netmask problem, but not really the one that other people
have described. This is how it usually works. Your troubled machine
above, "servername," receives an ARP who-has from another machine on
the LAN called "clientname." However, the IP address that clientname
gives as a source does not match up to any local networks that
servername knows about.

For example, say servername has an address of 192.0.2.10/25. The other
machine has 192.0.2.210/24. When servername gets an ARP (which is
broadcast so servername gets it fine),

  who-has 192.0.2.10 tell 192.0.2.210

It gets confused. 192.0.2.210 is not local (as far as it is concerned)
so it logs an error.

Note that this is not a harmless error. These two machine cannot talk
to each other.

The fix, of course, is to make sure all machines on the same LAN have
the same netmask.
-- 
Crist J. Clark                     |     cjclark@alum.mit.edu
                                   |     cjclark@jhu.edu
http://people.freebsd.org/~cjc/    |     cjc@freebsd.org

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