Chapter 26 Maintenance

For example, if a bridge receives a frame via port 1 from host A (MAC address 00a0c5123478), the bridge associates host A with port 1. When the bridge receives another frame on one of its ports with destination address 00a0c5123478, it forwards the frame directly through port 1 after checking the internal table.

The bridge takes one of these actions after it checks the destination address of an incoming frame with its internal table:

•If the table contains an association between the destination address and any of the bridge's ports aside from the one on which the frame was received, the frame is forwarded out the associated port.

•If no association is found, the frame is flooded to all ports except the inbound port. Broadcasts and multicasts also are flooded in this way.

•If the associated port is the same as the incoming port, then the frame is dropped (filtered).

26.7Transparent Firewalls

A transparent firewall (also known as a transparent, in-line, shadow, stealth or bridging firewall) has the following advantages over “router firewalls”:

1The use of a bridging firewall reduces configuration and deployment time because no networking configuration changes to your existing network (hosts, neighboring routers and the firewall itself) are needed. Just put it in-line with the network it is protecting. As it only moves frames between ports (after inspecting them), it is completely transparent.

2Performance is improved as there's less processing overhead.

3As a transparent bridge does not modify the frames it forwards, it is effectively “stealth” as it is invisible to attackers.

Bridging devices are most useful in complex environments that require a rapid or new firewall deployment. A transparent, bridging firewall can also be good for companies with several branch offices since the setups at these offices are often the same and it's likely that one design can be used for many of the networks. A bridging firewall could be configured at HQ, sent to the branches and then installed directly without additional configuration.

26.8 Configuring Device Mode (Router)

Click MAINTENANCE > Device Mode to open the following screen. Use this screen to configure your ZyWALL as a router or a bridge.

In router mode, the ZyWALL functions as a router. The ZyWALL routes traffic traveling between the ZyWALL's interfaces and filters and inspects packets.

In router mode, the ZyWALL can get an IP address from a DHCP server. It can also serve as a DHCP server to assign IP addresses to your local computers. The LAN, WAN, DMZ and WLAN interfaces all have different IP addresses. The ZyWALL also provides NAT, port forwarding, policy routing, and DNS in router mode. These features allow you to set up private network. See Table 5 on page 60 in the user’s guide for a detailed list of other features available in router mode.

The following applies when the ZyWALL is in router mode.

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ZyWALL 2 Plus User’s Guide