ZyXEL Communications NXC5200 User Manual page 194

Chapter 11 Interfaces
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.
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 NXC 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 NXC 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 NXC creates the following entry in the
routing table.
Table 67 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 NXC uses the gateway with the lowest metric, or cost. If two or more
gateways have the same metric, the NXC 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.
Interface Parameters
The NXC restricts the amount of traffic into and out of the NXC through each
interface.
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NXC5200 User's Guide