Chapter 10 Interface

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.

Table 85 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

 

 

 

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 265.

•Gateway - The interface provides the same gateway you specify for the interface. See IP Address Assignment on page 265.

•DNS servers - The interface provides IP addresses for up to three DNS servers that provide DNS services for DHCP clients. You can specify each IP address manually (for example, a company’s own DNS server), or you can refer to DNS servers that other interfaces received from DHCP servers (for example, a DNS server at an ISP). These other interfaces have to be DHCP clients.

It is not possible for an interface to be the DHCP server and a DHCP client simultaneously.

 

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ZyWALL USG 100/200 Series User’s Guide