Linux bridge mac address table


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Creating a bridge

Similar to hardware bridge, Linux bridge maintains a layer-2 forwarding table also known as MAC learning table, forwarding database, or just FDB , which keeps track of what MAC addresses are associated with which ports. That way, later when a bridge needs to forward a packet destined to address X, it knows where to forward the packet from FDB lookup.

You can check the current forwarding table or MAC learning table of a Linux bridge using the following command. This command will show a list of all learned MAC addresses along with their associated port number.

MAC Table - Background

Each entry has a corresponding aging timer attached to it, so that the forwarding entries get refreshed after some time, making the MAC learning table up-to-date. Delivery powered by Google Feedburner. The devices connected to the bridges do have MAC addresses. But I don't think the bridge itself need one. As for the rest of the answer, does that means that the bridge interface act as an additional "port" on the bridge which allows other ports to access the host machine?

The bridge is able to originate Ethernet frames, so it needs an address.

023 Basic networking ifconfig, ifup, ifdown, etc network interfaces

But is it mandatory that the bridge interface has a MAC address? I mean, a physical switch does not have to have a MAC address to do its job, does it? So I would think that the interface does not require one either. A simple bridge is effectively a two-port switch, so it does not necessarily need any addresses.


  • bridge(8) - Linux manual page.
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  • Adding an interface.
  • Linux Bridge - how it works.

A simple bridge does not originate frames, it just receives a frame on one port and either forwards it on the other port, or drops it. Why can't the primary NIC be still the connection to the outside world? Real hardware bridges also keep the IP address of the real link partners connected to them. Why not the linux wirtual bridge? Yes, the bridge interface acts as an additional port.

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After man 5 systemd. Sign up or log in Sign up using Google. The address mac address you give MUST be one of your enslaved ethernet cards.

networking - How to capture arp table when using network bridging? - Server Fault

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.

Do you see a rationale for the bridge MAC dance any way? To be honest, I don't know why the default behavior is to have a dynamic MAC address for the bridge. The important thing is that there is now the option of setting a sticky address.

This is great. I've been running into this problem on a new server and couldn't figure out what was causing it. Name required.

Using MAC table – Linux Bridge – WILT

Email will not be published required. Skip to content Home About Feed. Linux bridge: The old way is using ifconfig: Oseias Ferreira says: May 16, at Reply to this comment.

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