3Com 10014299 manual Obtain address table, Main Functions of Bridging

290CHAPTER 19: CONFIGURING BRIDGE

Main Functions of Bridging

■Supports bridging on the Frame Relay links.

■Supports bridging on the sub-interfaces of VLAN.

■Supports bridging on BDR and dialing standby.

■Supports binding of multiple ports and load sharing.

■Support both routing and bridging function for specified protocol.

■Support filtering Ethernet frames according to the MAC address or Ethernet frame format.

■Provides command configuration and management functions.

■Provides functions of logging, alarming and debugging.

Obtain address table

Bridging implements forwarding in accordance with the bridging table comprised of MAC addresses and interfaces. A bridge should obtain the correlation between MAC addresses and ports. When the bridge connects with a LAN segment, it will detect all the Ethernet frames on this segment. Once the Ethernet frame sent from a node is detected, the source MAC address of this frame will be picked up and the correlation between this MAC address and the interface receiving this frame will be added to the bridging address table.

As shown in the following figure, four workstations A, B, C and D are distributed in two LANs: Ethernet segment 1 connected with Bridge port 1 and Ethernet segment 2 connected with Bridge port 2. At a certain moment, when Workstation A transmits an Ethernet frame to Workstation B, both the bridge and Workstation B will receive this frame.

Figure 101 Workstation A transmits information to workstation B on the Ethernet segment 1

00e0.fcaa.aaaa		00e0.fcbb.bbbb
Workstation A		Workstation B
Source address Destination address
00e0.fcaa.aaaa00e0.fcbb.bbbb
	Bridge port 1	Ethernet segment 1
00e0.fccc.cccc		00e0.fcdd.dddd
Bridge		Workstation D
Workstation C
	Bridge port 2
		Ethernet segment 2

Upon receiving the Ethernet frame, the bridge learns that Workstation A is connected with Bridge port 1 since the frame received is from Port 1. As a result, the correlation between the MAC address of Workstation A and Bridge port 1 will be added to the bridging table, as shown in the following figure: