Linux bridge mac address table

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.


  • MAC Table - Background.
  • Your Answer.
  • Adding an interface;
  • league of legends mac black screen;
  • Creating a bridge.

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.

How to show a MAC learning table of Linux bridge - Ask Xmodulo

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. 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.

how to create second nic (create 2nd or alias nic: eth0:1 in linux)

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. The old way is using ifconfig:. Thanks for the useful post.

Using MAC table – Linux Bridge – WILT

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. Did you find this tutorial helpful? Then please be generous and support Xmodulo!

Linux bridge: MAC addresses and dynamic ports

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Notify me of follow-up comments by email. Notify me of new posts by email. Step 2: In the output, each row represents MAC address learnt at each port of the Linux bridge.

Step 3: And Ports 2 and 3 represent the Tap interfaces on the Linux bridge myvirtbridge. Step 4: Similarly for local port 3. Step 5: