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290 CHAPTER 19: CONFIGURING BRIDGE
■ 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.
Main Functions of
Bridging
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
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:
Bridge
00e0.fcaa.aaaa00e0.fcbb.bbbb
Source address
Destination address
Ethernet segment 1
Bridge port 1
Bridge port 2
00e0.fccc.cccc
00e0.fcdd.dddd
Ethernet segment 2
00e0.fcaa.aaaa
00e0.fcbb.bbbb
Workstation A
Workstation B
Workstation C
Workstation D