Swapping MAC addresses?

Chase Bolt cbolt at datinggold.com
Thu Sep 3 12:33:04 CDT 2009


Doing the ARP fix is, in my opinion, the best option. Though you can do 
bonding or a subinterface. If you do a subinterface just make sure that 
a single interface can handle the load that was originally placed on both.


John Oliver wrote:
> On Thu, Sep 03, 2009 at 09:53:06AM -0700, John LLOYD wrote:
>   
>>> [joliver at mda-services ~]$ sudo cat
>>> /etc/sysconfig/network-scripts/ifcfg-eth0
>>> # Broadcom Corporation NetXtreme II BCM5708 Gigabit Ethernet
>>> DEVICE=eth0
>>> HWADDR=00:19:b9:ca:5b:44
>>> IPADDR=XXXXXXXXX.129
>>>       
>> ...snip...
>>     
>>> [joliver at mda-services ~]$ sudo cat
>>> /etc/sysconfig/network-scripts/ifcfg-eth1
>>> # Broadcom Corporation NetXtreme II BCM5708 Gigabit Ethernet
>>> DEVICE=eth1
>>> HWADDR=00:19:B9:CA:5B:46
>>> IPADDR=XXXXXXXXX.47
>>>       
>> There's your problem -- they are on the same subnet, no?  (your '129 IP
>> and '47 IP have the same left-hand side).  You have two NICs on the same
>> subnet.
>>
>> You need to bond them, or disconnect one, or adjust some ARP tuning,
>> e.g. arp_filter=1 to force one or the other (only) to respond to arp
>> requests.
>>
>> (Think of it from the linux kernel point of view.  It has a packet in
>> hand, ready to go out to your subnet XXXXXXXX.  Which interface should
>> it use?  It has a choice of two, so, clearly, it is changing it's mind
>> from week to week....)
>>     
>
> I've had this config for months.  This issue cropped up about a month
> ago.
>
> I can probably get away with making one IP a subinterface.  I did it
> this way because I was under the impression that, on this network, MAC
> addresses and IPs were inextricably bound (hard config in the switch).
> I'll have to check with the network guys.
>
> Thanks for pointing this out!
>
>   
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