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Bridge Overview 293
Figure 106 Filter (not forward)
■ Suppose that Workstation A sends an Ethernet frame to Workstation C, and
the bridge does not find the correlation between the MAC address of
Workstation C and the port in the bridging address table, what will the bridge
do? The bridge will forward this frame destined to an unknown MAC address
to all ports except the one on which it is received. In this case, the bridge
actually plays the role of a hub to make sure the continuous information
transmission, as shown in the following figure:
Figure 107 No matched MAC address is found in the bridging table
Eliminating loop
As shown in the following figure, both bridges X and Y are connected with
Ethernet segment 1. Once detecting a broadcasting frame, both bridges will send
it to all ports except the source port on which the frame is detected. That is, both
bridges X and Y will forward this broadcast frame.
No forwarding
Bridge
Ethernet segment 1
Bridge port 1
Bridge port 2
Ethernet segment 2
00e0.fcaa.aaaa 00e0.fcbb.bbbb
Source address
Destination address
Bridging table
MAC
address
00e0.fcbb.bbbb
00e0.fccc.cccc
00e0.fcdd.dddd
00e0.fcaa.aaaa
Port
1
1
2
2
Workstation A Workstation B
Workstation C Workstation D
00e0.fcaa.aaaa
00e0.fcbb.bbbb
00e0.fcdd.dddd
Bridge
Ethernet segment 1
Bridge port 1
Bridge port 2
00e0.fccc.cccc
00e0.fcdd.dddd
Ethernet segment 2
00e0.fcaa.aaaa
00e0.fcbb.bbbb
00e0.fcaa.aaaa
00e0.fccc.cccc
Source address
Destination address
Bridging table
MAC
address
00e0.fcaa.aaaa
Port
1
1
00e0.fcbb.bbbb