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I have created a bridge using to existing network interfaces:

$ brctl addif br0 eth1
$ brctl addif br0 eth2

Why do eth1 and eth2 lose their IP addresses? What's the reasoning behind it?

PS this is on Ubuntu Linux.

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up vote 4 down vote accepted

When a device is part of a bridge the IP address is set on the bridge rather than on the individual devices, because that is where packets can enter from the host system or exit to the host system.

A bridge is basically just a virtual ethernet switch with both the bridge device, and each device that is added to it, being a port on that switch. The bridge device (br0 in this case) is then the switch port which is connected to your computer and which can be given an address and used to send and receive packets.

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Thanks for the answer. – fazineroso Dec 13 '12 at 10:31

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