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in-reply-to: <925A849792280C4E80C5461017A4B8A20321F5@mail733.InfraSupportEtc.com>
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Subject: RE: Router stops routing after changing MAC Address
Date: Mon, 13 Mar 2006 16:39:16 -0500
Message-ID: <Pine.LNX.4.61.0603131636470.5608@chaos.analogic.com>
Thread-Topic: Router stops routing after changing MAC Address
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References: <925A849792280C4E80C5461017A4B8A20321F5@mail733.InfraSupportEtc.com>
From: "linux-os \(Dick Johnson\)" <linux-os@analogic.com>
To: "Greg Scott" <GregScott@InfraSupportEtc.com>
Cc: "Stephen Hemminger" <shemminger@osdl.org>,
       "Chuck Ebbert" <76306.1226@compuserve.com>,
       "linux-kernel" <linux-kernel@vger.kernel.org>,
       "David S. Miller" <davem@davemloft.net>, <netdev@vger.kernel.org>,
       "Bart Samwel" <bart@samwel.tk>, "Alan Cox" <alan@lxorguk.ukuu.org.uk>,
       "Simon Mackinlay" <smackinlay@mail.com>
Reply-To: "linux-os \(Dick Johnson\)" <linux-os@analogic.com>
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On Mon, 13 Mar 2006, Greg Scott wrote:

> But in a failover scenario you want two devices to have the same IEEE
> (station) Address (or MAC Address or hardware address).  So many names
> for the same thing!
>
> When the primary unit fails, you want the backup unit to completely
> assume the failed unit's identity - right down to the MAC Address.  The
> other way to do it using gratuitous ARPs is not good enough because some
> cheap router someplace with an ARP cache of several hours will not
> listen and will never update its own ARP cache.
>
> I like to think of this as bending the rules a little bit, not really
> breaking them.  :)
>
> - Greg
>

Top posting, NotGood(tm). Anyway, if the device fails, you have
routers and hosts ARPing the interface, trying to establish a
route anyway.

>
>
>> Actually, it doesn't make any difference. Changing the IEEE station
>> (physical) address is not an allowed procedure even though hooks are
>> available in many drivers to do this. According to the IEEE 802
>> physical media specification, this 48-bit address must be unique
>> and must be one of a group assigned by IEEE. Failure to follow this
>> simple protocol can (will) cause an entire network to fail. If you
>> don't care, then you certainly don't care about multicast bits either,
>> basically let them set it to all ones as well.
>
>> Cheers,
>> Dick Johnson
>> Penguin : Linux version 2.6.15.4 on an i686 machine (5589.54 BogoMips).
>> Warning : 98.36% of all statistics are fiction, book release in April.
>

Cheers,
Dick Johnson
Penguin : Linux version 2.6.15.4 on an i686 machine (5589.54 BogoMips).
Warning : 98.36% of all statistics are fiction, book release in April.
_


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