ZyXEL Communications ZyWall USG 2000 User Manual page 221

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 140 Example: Entry in the Routing Table Derived from Interfaces
Table 65 Example: Routing Table Entries for Interfaces
IP ADDRESS(ES)
100.100.1.1/16
200.200.200.1/24
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
ZyWALL USG 2000 User's Guide
DESTINATION
ge1
ge2
Chapter 10 Interfaces
221