Chapter 10 Interface

Figure 122 Example: Entry in the Routing Table Derived from Interfaces

Table 44 Example: Routing Table Entries for Interfaces

IP ADDRESS(ES)

DESTINATION

100.100.1.1/16

ge1

 

 

200.200.200.1/24

ge2

 

 

For example, if the ZyWALL gets a packet with a destination address of 100.100.25.25, it routes the packet to interface ge1. If the ZyWALL gets a packet with a destination address of 200.200.200.200, it routes the packet to interface ge2.

In most interfaces, you can enter the IP address and subnet mask manually. In PPPoE/PPTP interfaces, however, the subnet mask is always 255.255.255.255 because it is a point-to-point interface. For these interfaces, you can only enter the IP address.

In many interfaces, you can also let the IP address and subnet mask be assigned by an external DHCP server on the network. In this case, the interface is a DHCP client. Virtual interfaces, however, cannot be DHCP clients. You have to assign the IP address and subnet mask manually.

In general, the IP address and subnet mask of each interface should not overlap, though it is possible for this to happen with DHCP clients.

In the example above, if the ZyWALL gets a packet with a destination address of 5.5.5.5, it might not find any entries in the routing table. In this case, the packet is dropped. However, if there is a default router to which the ZyWALL should send this packet, you can specify it as a gateway in one of the interfaces. For example, if there is a default router at 200.200.200.100, you can create a gateway at 200.200.200.100 on ge2. In this case, the ZyWALL creates the following entry in the routing table.

Table 45 Example: Routing Table Entry for a Gateway

IP ADDRESS(ES)

DESTINATION

0.0.0.0/0

200.200.200.100

 

 

The gateway is an optional setting for each interface. If there is more than one gateway, the ZyWALL uses the gateway with the lowest metric, or cost. If two or more gateways have the same metric, the ZyWALL uses the one that was set up first (the first entry in the routing table). In PPPoE/PPTP interfaces, the other computer is the gateway for the interface by default. In this case, you should specify the metric.

If the interface gets its IP address and subnet mask from a DHCP server, the DHCP server also specifies the gateway, if any.

 

181

ZyWALL USG 1000 User’s Guide