Swapping MAC addresses?

John Oliver joliver at john-oliver.net
Thu Sep 3 12:29:22 CDT 2009


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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* John Oliver                             http://www.john-oliver.net/ *
*                                                                     *
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