3Com 10014299 manual Eliminating loop, Filter not forward

			Bridge Overview 293
Figure 106 Filter (not forward)
00e0.fcaa.aaaa			00e0.fcbb.bbbb
Workstation A			Workstation B
Source address Destination address
	00e0.fcaa.aaaa	00e0.fcbb.bbbb

Bridging table

Bridge port 1

Ethernet segment 1

MAC address	Port
00e0.fcaa.aaaa	1
00e0.fcbb. bbbb	1
00e0.fccc . cccc	2
00e0.fcdd.dddd	2

Workstation C

Bridge00e0.fcdd.dddd

No forwarding

Bridge port 2 Workstation D

Ethernet segment 2

■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

00e0.fcaa.aaaa 00e0.fcbb.bbbb

Source address Destination address 00e0.fcaa.aaaa 00e0.fccc.cccc

00e0.fccc.cccc

Bridging table

MAC address	Port
00e0.fcaa.aaaa	1
00e0.fcbb.bbbb	1

Bridge port 1	Ethernet segment 1
Bridge	00e0.fcdd.dddd
Bridge port 2

Ethernet segment 2

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.