[Bridge] Fwd: What is the lowest valid MAC address that can be assigned to a NIC/bridge?

[Bridge] Fwd: What is the lowest valid MAC address that can be assigned to a NIC/bridge?

[Chandrashekarappa]

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My setup:
I have a machine running RHEL 5.4(kernel - 2.6.18-164.el5)with two NICs.I've
created a bonded interface bond0 with the 2 NICs(eth0 and eth1),added bond0
to the bridge br0.

When I create the bonded interface bond0,bond0 gets the MAC address of the
first slave device(eth0 in my case)
After I create br0 and add bond0 to br0,br0 gets the MAC address of bond0.

Issue:
-I then add a third ethernet interface eth2 to br0
-br0 now acquires the MAC address of eth2
-I'd like it if the MAC address of br0 *didn't change*.

My analysis:
-A bridge acquires the lowest MAC address of all the ports connected to
it.So,I do believe the bridge acquiring a new MAC address every time an
ethernet interface is added or removed from a bridge is expected.
-I also found this patch in the 2.6.27 upstream kernel :
92c0574f11598c8036f81e27d2e8bdd6eed7d76d
bridge: make bridge address settings sticky

Normally, the bridge just chooses the smallest mac address as the
bridge id and mac address of bridge device. But if the administrator
has explictly set the interface address then don't change it.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Possible workaround:
I think I should be able to work around this issue by assigning the lowest
valid MAC address to one of my ethernet interfaces before adding it to
br0.I'd like to know what is the lowest valid MAC address that can be
assigned to a NIC.
http://standards.ieee.org/regauth/groupmac/tutorial.html

I'd appreciate any pointers.

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Re: [Bridge] Fwd: What is the lowest valid MAC address that can be assigned to a NIC/bridge?

[richardvoigt]

The "lowest valid MAC address" is assuredly not unique to the host,
which I would think rather defeats the purpose of using it as an
address.

On Mon, Mar 8, 2010 at 3:32 PM, Chandrashekarappa <nandinic1@gmail.com> wrote:
>
> My setup:
> I have a machine running RHEL 5.4(kernel - 2.6.18-164.el5)with two NICs.I've
> created a bonded interface bond0 with the 2 NICs(eth0 and eth1),added bond0
> to the bridge br0.
>
> When I create the bonded interface bond0,bond0 gets the MAC address of the
> first slave device(eth0 in my case)
> After I create br0 and add bond0 to br0,br0 gets the MAC address of bond0.
>
> Issue:
> -I then add a third ethernet interface eth2 to br0
> -br0 now acquires the MAC address of eth2
> -I'd like it if the MAC address of br0 *didn't change*.
>
> My analysis:
> -A bridge acquires the lowest MAC address of all the ports connected to
> it.So,I do believe the bridge acquiring a new MAC address every time an
> ethernet interface is added or removed from a bridge is expected.
> -I also found this patch in the 2.6.27 upstream kernel :
> 92c0574f11598c8036f81e27d2e8bdd6eed7d76d
> bridge: make bridge address settings sticky
>
> Normally, the bridge just chooses the smallest mac address as the
> bridge id and mac address of bridge device. But if the administrator
> has explictly set the interface address then don't change it.
>
> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
>
> Possible workaround:
> I think I should be able to work around this issue by assigning the lowest
> valid MAC address to one of my ethernet interfaces before adding it to
> br0.I'd like to know what is the lowest valid MAC address that can be
> assigned to a NIC.
> http://standards.ieee.org/regauth/groupmac/tutorial.html
>
> I'd appreciate any pointers.
>
>
> _______________________________________________
> Bridge mailing list
> Bridge@lists.linux-foundation.org
> https://lists.linux-foundation.org/mailman/listinfo/bridge
>

Re: [Bridge] Fwd: What is the lowest valid MAC address that can be assigned to a NIC/bridge?

[Stephen Hemminger]

On Mon, 8 Mar 2010 16:03:15 -0600
"richardvoigt@gmail.com" <richardvoigt@gmail.com> wrote:

> The "lowest valid MAC address" is assuredly not unique to the host,
> which I would think rather defeats the purpose of using it as an
> address.

Agreed. I would choose one of the existing interfaces and set
that value explicitly.


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