An Ethernet bridge is a device for forwarding packets between two or more Ethernets so that they behave in most respects as if they were a single network. It could be a physical device, but it is also possible for a bridge to be implemented entirely in software. The Linux kernel has the ability to perform bridging by means of the bridge module.

Bridges normally try to avoid forwarding traffic unless it needs to appear on another network segment. This helps to conserve bandwidth and improves security, but you should not rely on it: broadcast traffic is always forwarded, and non-broadcast traffic may be forwarded if the bridge does not know which port the destination is attached to.

When a bridge is added to a network it is very important to ensure that no loops are created, otherwise traffic may circulate indefinitely or replicate uncontrollably. If there is a possibility of this happening then you should use the Spanning Tree Protocol (STP) or one of its derivatives to detect and break loops automatically.


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