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Chapter 10 Interface
ZyWALL USG 300 User’s Guide
181
Figure 122 Example: Entry in the Routing Table Derived from Interfaces
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.
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.
Table 44 Example: Routing Table Entries for Interfaces
IP ADDRESS(ES) DESTINATION
100.100.1.1/16 ge1
200.200.200.1/24 ge2
Table 45 Example: Routing Table Entry for a Gateway
IP ADDRESS(ES) DESTINATION
0.0.0.0/0 200.200.200.100