netdev - RE: [PATCH 19/25] mlx4: Randomizing mac addresses for slaves

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Message-ID: <2ED289D4E09FBD4D92D911E869B97FDD0166CA59@mtlexch01.mtl.com>
Date:	Thu, 5 Nov 2009 15:38:18 +0200
From:	"Liran Liss" <liranl@...lanox.co.il>
To:	"Or Gerlitz" <or.gerlitz@...il.com>,
	"Roland Dreier" <rdreier@...co.com>
Cc:	"Yevgeny Petrilin" <yevgenyp@...lanox.co.il>,
	<linux-rdma@...r.kernel.org>, <netdev@...r.kernel.org>,
	"Tziporet Koren" <tziporet@...lanox.co.il>
Subject: RE: [PATCH 19/25] mlx4: Randomizing mac addresses for slaves

This approach seems to be common practice now (e.g., drivers/net/igb/igb_main.c:1332).
In any case, the user can change the randomized mac.
--Liran

-----Original Message-----
From: Or Gerlitz [mailto:or.gerlitz@...il.com] 
Sent: Wednesday, November 04, 2009 11:33 PM
To: Roland Dreier
Cc: Yevgeny Petrilin; linux-rdma@...r.kernel.org; netdev@...r.kernel.org; Liran Liss; Tziporet Koren
Subject: Re: [PATCH 19/25] mlx4: Randomizing mac addresses for slaves

On Wed, Nov 4, 2009 at 10:04 PM, Roland Dreier <rdreier@...co.com> wrote:
>> +#define MLX4_MAC_HEAD               0x2c9000000ULL

> Is this a good idea?  You're basically choosing 24 random bits within your OUI...
> seems the chance of collision with another MAC used on the same 
> network is high enough that it could easily happen in practice on a moderately big network.

yes, this has been brought by Stephen and others on this last back on September 11th, this year @
http://marc.info/?l=linux-netdev&m=125263488409128

> Can you pick a reserved range or something?

Using different OUI for the VF device wouldn't help either I think, since the #VF becomes fairly big even on a modest side cluster with
(say) a VM consuming VF per 1-2 cores.

Or.
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