Bridge Interfaces - ZyXEL Communications ZYWALL USG 20 Manual

Chapter 11 Interfaces

11.9 Bridge Interfaces

This section introduces bridges and bridge interfaces and then explains the
screens for bridge interfaces.
Bridge Overview
A bridge creates a connection between two or more network segments at the
layer-2 (MAC address) level. In the following example, bridge X connects four
network segments.
When the bridge receives a packet, the bridge records the source MAC address
and the port on which it was received in a table. It also looks up the destination
MAC address in the table. If the bridge knows on which port the destination MAC
address is located, it sends the packet to that port. If the destination MAC address
is not in the table, the bridge broadcasts the packet on every port (except the one
on which it was received).
In the example above, computer A sends a packet to computer B. Bridge X
records the source address 0A:0A:0A:0A:0A:0A and port 2 in the table. It also
looks up 0B:0B:0B:0B:0B:0B in the table. There is no entry yet, so the bridge
broadcasts the packet on ports 1, 3, and 4.
Table 67 Example: Bridge Table After Computer A Sends a Packet to Computer B
MAC ADDRESS
0A:0A:0A:0A:0A:0A
274
PORT
2
ZyWALL USG 20/20W User's Guide