RE: [Hampshire] One box, 2 NICs - but with the same MAC addr…

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Author: Bond, Peter
Date:  
To: Hampshire LUG Discussion List
Subject: RE: [Hampshire] One box, 2 NICs - but with the same MAC address
> -----Original Message-----
> From: hampshire-bounces@???
> [mailto:hampshire-bounces@mailman.lug.org.uk]On Behalf Of
> David Ramsden


> I don't quite understand what is trying to be acheived. Is this to
> implement a failover solution? If one network card fails, you
> can go and
> physically unplug the cable from one NIC and place it in the
> other and
> then ifup the interface?


Essentially, yes. Both interfaces to be live simultaneously, with one taking over as active master on network outage. No definition yet on what an outage constitutes - could just be link down.

> What was the reasoning behind giving both NICs the same MAC
> address? The
> only reason I can think of is either your switches and/or routing
> equipment have been implemented to only allow access from known MAC
> addresses or to try to reduce the downtime if a NIC fails
> because if you
> unplug one NIC and plug in another with the same IP address,
> ARP tables
> won't have timed out and the box won't be seen on the network.


I don't have a justification for it yet, just an arbitrary requirement. Closest I've got is "some people don't like having to buy dedicated routers".

> If my understanding is correct then this sounds like a
> horrible solution
> and will introduce more administrative overhead.


Oooh no, I've got to implement it so it's fully autonomous...

> You want to look in to bonding, where you can have two NICs
> for example,
> both plugged in to the same physical network. When bonding has been
> implemented you will see one logical interface. However, if one NIC
> fails everything should continue to work as normal. Note the *should*
> :-) You may find you need switches that support link aggregation.


I'm not sure that bonding is quite what is going on here - it's some horrible offspring of bonding as defined so far. IP aliasing is a start point for this, but there is still MAC takeover "needed".

Peter

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