ZyXEL Communications 200 Series - Manual (Page 255)

Chapter 10 Interface
ZyWALL USG 100/200 Series User’s Guide
255
10.13 Bridge Interface Screen
A bridge creates a connection between two or more network segments at the layer-2 (MAC
address) level.
Unlike the device-wide bridge mode in ZyNOS-based ZyWALLs, this ZyWALL can bridge
traffic between some interfaces while it routes traffic for other interfaces. The bridge
interfaces also support more functions, like interface bandwidth parameters, DHCP settings,
and ping check. To use the whole ZyWALL as a transparent bridge, add all of the ZyWALL’s
interfaces to a bridge interface.
In the following example, bridge X connects four network segments.
Figure 180 Bridge Example
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.
If computer B responds to computer A, bridge X records the source address
0B:0B:0B:0B:0B:0B and port 4 in the table. It also looks up 0A:0A:0A:0A:0A:0A in the table
and sends the packet to port 2 accordingly.
Table 76 Example: Bridge Table After Computer A Sends a Packet to Computer B
MAC ADDRESS PORT
0A:0A:0A:0A:0A:0A 2
Table 77 Example: Bridge Table After Computer B Responds to Computer A
MAC ADDRESS PORT
0A:0A:0A:0A:0A:0A 2
0B:0B:0B:0B:0B:0B 4