Cabletron Systems NB20E, NB25 E user manual 1 Bridging Method, Node A, Node C, Lan Node B

INTRODUCTION

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NODE A		NODE C
	LAN 1

LAN 2

NODE B

Figure 1-1 Bridging Method

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In this example, when Node A sends a packet to Node B, the bridge learns Node A’s source address and adds the address to the Source Address Table, indicating that the node is on LAN 1. If Node C subsequently sends a packet to Node A, Node A’s address will be detected in the Source Address Table for LAN 1 and the packet will not be forwarded across the bridge to LAN 2. At the same time, the bridge will learn Node C’s source address and add it to the Source Address Table, indicating that the node is on LAN 1.

If the destination address of a packet is located on a different segment, the bridge will forward the packet across the bridge. If Node B sends a packet to Node A, the bridge will compare the destination address of the packet against the addresses in the Source Address Table. It will then detect Node A as being on the other side of the bridge and forward the packet through the bridge to LAN 1. The bridge will store the address of Node B to indicate that Node B is on LAN 2.

If no packets are sent from a source address in a five minute interval, that address will be deleted from the bridge’s Source Address Table.

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