Br0 eth0 same mac address

Installing the software

You can cross-check the enumeration of your ethernet devices with eth0 , eth1 , etc. Use brctl: Simple enough. This file describes the network interfaces available on your system and how to activate them. For more information, see interfaces 5. The loopback network interface auto lo iface lo inet loopback Set up interfaces manually, avoiding conflicts with, e. For example: The loopback network interface auto lo br0 iface lo inet loopback Set up interfaces manually, avoiding conflicts with, e.

In some cases you may need to tweak these variables. There are two common options: It's often desirable to share a physical network interface with guests by creating a bridge. This usually offers excellent performance and doesn't require NAT. This operation is composed of two parts: Setup the bridge interface on host as described in this article, here or here Configure guest to use the newly-created bridge The libvirt Networking Handbook provides thorough instructions.

You can verify if bridging is working properly by looking at brctl output: The virbr0 interface is only used by libvirt to give guests NAT connectivity. Bridging with a wireless NIC Just like you can bridge two wired ethernet interfaces, you can bridge between an ethernet interface and a wireless interface. In our case, this allows to change the source MAC address of all of our frames. This is handy because we fool our AP into thinking that all of our forwarded frames come from the machine which authenticated to the AP.

The problem is, the host seems to randomly suffer some loss of connectivity from a few to seconds when some guest is started or stopped. Initially one might think of something related to STP, but it turns out that it is disabled and even then, ports appearing or disappearing should not affect existing ports. What happens here is that, when a new guest is started, a tap interface is created and enslaved to the bridge the tap interface is usually connected to the guest's own ethernet interface. This interface has a name like vnet5 , for example. Minor but important detail, this tap interface has a more or less random MAC address.

Note that we're talking of the host-side tap interface, not the guest-side virtual interface, whose MAC address is configurable in the guest's configuration file or on the command line.

Your Answer

It is theoretically possible to set the MAC address of this host-side tap interface, but it's quite involved and basically nobody does that and also virt-manager has no provision to do that. So if the newly created interface has a lower MAC, the bridge changes its MAC address and uses that of the new interface.

When the guest is stopped, the tap interface is removed from the bridge and destroyed, at which point the bridge's MAC address has to change again. Depending on the traffic patterns, this may take anything from a few seconds to several tens of seconds.

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Fortunately, there is a way to ensure that the bridge's MAC address is fixed and never changes, thus entirely avoiding the problem. Thanks to this thread and this thread by people with similar problems, I found out that if the bridge's MAC address is forced to a specific value, the bridge "remembers" that and makes the address permanent.

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But there's a caveat: In our example and probably also in the most common case , the ideal candidate is obviously eth0 , which is permanently enslaved. There are two ways to set the MAC address of an interface.



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The old way is using ifconfig:. Thanks for the useful post. This scenario also applies to OpenVZ containers when configured with veth devices. Your post and the post at http: It probably fails now, because eth1 is not yet configured when the command is executed.

[ovs-discuss] Same mac address of br0 and eth0

Your line is commented and it works, if i get out the comment it just stops working There is a bond-bridge setup of eth1 and eth0, bond-mode 1 redundance OK, IT works, I had a typo in address! The address mac address you give MUST be one of your enslaved ethernet cards. This is probably for some sort of security reasons, so you can't spoof and create chaos in the network by artificially replicating the same mac.

I mistyped a character to be sure of that: Actually one should read "post-up ip link Thank you very much for these very clear and detailled explanations. This problem was annoying me for a while.