ZyXEL Communications ZyXEL ZyWALL USG-1000, User Manual

Page: 223 / 986

Chapter 10 Interfaces
ZyWALL USG 2000 User’s Guide
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computers in the network. This reduces the amount of manual configuration you
have to do and usually uses available IP addresses more efficiently.
In DHCP, every network has at least one DHCP server. When a computer (a DHCP
client) joins the network, it submits a DHCP request. The DHCP servers get the
request; assign an IP address; and provide the IP address, subnet mask, gateway,
and available network information to the DHCP client. When the DHCP client
leaves the network, the DHCP servers can assign its IP address to another DHCP
client.
In the ZyWALL, some interfaces can provide DHCP services to the network. In this
case, the interface can be a DHCP relay or a DHCP server.
As a DHCP relay, the interface routes DHCP requests to DHCP servers on different
networks. You can specify more than one DHCP server. If you do, the interface
routes DHCP requests to all of them. It is possible for an interface to be a DHCP
relay and a DHCP client simultaneously.
As a DHCP server, the interface provides the following information to DHCP
clients.
• IP address - If the DHCP client’s MAC address is in the ZyWALL’s static DHCP
table, the interface assigns the corresponding IP address. If not, the interface
assigns IP addresses from a pool, defined by the starting address of the pool
and the pool size.
The ZyWALL cannot assign the first address (network address) or the last
address (broadcast address) in the subnet defined by the interface’s IP address
and subnet mask. For example, in the first entry, if the subnet mask is
255.255.255.0, the ZyWALL cannot assign 50.50.50.0 or 50.50.50.255. If the
subnet mask is 255.255.0.0, the ZyWALL cannot assign 50.50.0.0 or
50.50.255.255. Otherwise, it can assign every IP address in the range, except
the interface’s IP address.
If you do not specify the starting address or the pool size, the interface the
maximum range of IP addresses allowed by the interface’s IP address and
subnet mask. For example, if the interface’s IP address is 9.9.9.1 and subnet
mask is 255.255.255.0, the starting IP address in the pool is 9.9.9.2, and the
pool size is 253.
• Subnet mask - The interface provides the same subnet mask you specify for the
interface. See IP Address Assignment on page 221 .
Table 67 Example: Assigning IP Addresses from a Pool
START IP ADDRESS POOL SIZE RANGE OF ASSIGNED IP ADDRESS
50.50.50.33 5 50.50.50.33 - 50.50.50.37
75.75.75.1 200 75.75.75.1 - 75.75.75.200
99.99.1.1 1023 99.99.1.1 - 99.99.4.255
120.120.120.100 100 120.120.120.100 - 120.120.120.199