ZyXEL Communications USG40 User Manual page 355

IP Address Assignment
Most interfaces have an IP address and a subnet mask. This information is used to create an entry
in the routing table.
Figure 250 Example: Entry in the Routing Table Derived from Interfaces
Table 127 Example: Routing Table Entries for Interfaces
IP ADDRESS(ES)
100.100.1.1/16
200.200.200.1/24
For example, if the ZyWALL/USG gets a packet with a destination address of 100.100.25.25, it
routes the packet to interface lan1. If the ZyWALL/USG gets a packet with a destination address of
200.200.200.200, it routes the packet to interface wan1.
In most interfaces, you can enter the IP address and subnet mask manually. In PPPoE/PPTP/L2TP
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/USG 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/USG 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/USG creates the
following entry in the routing table.
Table 128 Example: Routing Table Entry for a Gateway
IP ADDRESS(ES)
0.0.0.0/0
The gateway is an optional setting for each interface. If there is more than one gateway, the
ZyWALL/USG uses the gateway with the lowest metric, or cost. If two or more gateways have the
same metric, the ZyWALL/USG uses the one that was set up first (the first entry in the routing
table). In PPPoE/PPTP/L2TP interfaces, the other computer is the gateway for the interface by
default. In this case, you should specify the metric.
Chapter 10 Interfaces
lan1
DESTINATION
lan1
wan1
DESTINATION
200.200.200.100
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wan1