Strange kernel messages?

Kevin O'Connor kevin at ziptek-technologies.co.uk
Tue Aug 10 12:29:36 BST 2004


>-----Original Message-----
>From: freebsd-users-admin at uk.freebsd.org [mailto:freebsd-users-
>admin at uk.freebsd.org] On Behalf Of Grant
>Sent: 10 August 2004 11:44
>To: kevin at ziptek-technologies.co.uk
>Cc: freebsd-users at uk.freebsd.org
>Subject: Re: Strange kernel messages?
>
>Kevin O'Connor wrote:
>
>>It's just arp telling you that both nics are on the same network.
>>This will stop arp messages being logged
>>
>>Sysctl net.link.ether.inet.log_arp_movements=0
>>
>>Of course sorting out the problem would be better, it's never a good idea
>to
>>run 2 completely different subnets through the same hub
>>Regards
>>Kevin
>>
>>
>>>-----Original Message-----
>>>From: freebsd-users-admin at uk.freebsd.org [mailto:freebsd-users-
>>>admin at uk.freebsd.org] On Behalf Of Grant
>>>Sent: 10 August 2004 11:24
>>>To: freebsd-users at uk.freebsd.org
>>>Subject: Strange kernel messages?
>>>
>>>Hi,
>>>
>>>Got a few freebsd servers and i have noticed quite alot of these
>>>messages on the console and in the logs.
>>>
>>>arp: 10.0.0.100 moved from 00:c0:4f:26:a8:83 to 00:08:c7:3b:67:93 on fxp0
>>>arp: 10.0.0.100 moved from 00:08:c7:3b:67:93 to 00:c0:4f:26:a8:83 on fxp0
>>>arp: 10.0.0.100 moved from 00:c0:4f:26:a8:83 to 00:08:c7:3b:67:93 on fxp0
>>>
>>>There is two networks one 10.0.0.0/255.0.0.0 and the second
>>>192.168.254.0/255.255.255.0
>>>
>>>The ip 10.0.0.100 is a proxy/gateway running clarkconnect with dual
>>>network cards one on 10.0.0.100 and one 192.168.254.100
>>>
>>>The messages only seem to show up on the freebsd boxes, there is 3 boxes
>>>that show these messages.
>>>
>>>The first is 10.0.0.222 which has dual cards with the other interface at
>>>192.168.254.1
>>>The second box only has one card with ip of 10.0.0.60
>>>The third box only one card again with ip 10.0.0.70
>>>
>>>These machines are all linked to a 24port 3Com hub... just in case that
>>>is the problem :(
>>>
>>>The question is what is it ? and should i be worried at the amount i am
>>>getting of them ? and can it be stopped ?
>>>
>>>Thanks
>>>Grant.
>>>
>>>ps - The first box runs 4.10 and the second and third are running 5.2.1
>>>There is some linux boxes but they dont show any of the messages.
>>>
>>>
>>>------ FreeBSD UK Users' Group  -  Mailing List ------
>>>http://listserver.uk.freebsd.org/mailman/listinfo/freebsd-users
>>>
>>>
>>
>>
>>
>>
>Hey,
>
>Thanks for the quick reply!
>
>So maybe just get myself another hub and then put all the 10.0.0.0
>network on that and leave the 192.168.254.0 on the original hub ?
>
>I still dont quite get why i get them though as they are on different
>networks the subnets are different and so is the ranges... would a
>switch help instead of a hub ?
>
>Thanks
>Grant.
>
>

Ah you want to know why, this comes up every year or so.
Lets assume fxp0 and fxp1 are on the 10.0.0.0/8 network and fxp2 and fxp3
are on the 192.168.254.0/24 network. (Just 2 boxes in this example)
If fxp1 says hello I'm here fxp0 gets the message and builds an arp entry 
In the form
IP address MAC address 
so far no problem but you have routing enabled and that is saying if you
want to reach the 10.0.0.0/8 network route through fxp2 or fxp3 (internal to
the boxes) and that gives a different MAC address.You have two routes to the
different networks one internal and the other external through the hub. So
what is happening is you are building one arp entry for the internal route
and then scrapping it and building a new entry from the external route. This
is not a fault it is nothing to worry about in this case.

This answer is very simplistic and is only designed to allow you to
visualize the problem. To fully understand the problem you will need to do
quite a bit of reading.

If you wish to use a switch it will need to be layer 3 to allow it to be
split between the two networks. Two hubs or layer 2 switches will solve it
as well.
Hope this helps.
Regards
Kevin





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