Dhcp Configuration - ZyXEL Communications Prestige 642 User Manual

Prestige 642 ADSL Internet Access Router

3.2.4 DHCP Configuration

DHCP (Dynamic Host Configuration Protocol) allows the individual clients (workstations) to obtain the
TCP/IP configuration at start-up from a centralized DHCP server. The Prestige has built-in DHCP server
capability, enabled by default, which means it can assign IP addresses, an IP default gateway and DNS
servers to Windows 95, Windows NT and other systems that support the DHCP client. The Prestige can
also act as a surrogate DHCP server where it relays IP address assignment from the actual DHCP server to
the clients.
IP Pool Setup
The Prestige is pre-configured with a pool of 32 IP addresses starting from 192.168.1.33 to 192.168.1.64 for
the client machines. This leaves 31 IP addresses, 192.168.1.2 to 192.168.1.32 (excluding the Prestige itself
which has a default IP of 192.168.1.1) for other server machines, e.g., server for mail, FTP, telnet, web,
etc., that you may have.
DNS Server Address
DNS (Domain Name System) is for mapping a domain name to its corresponding IP address and vice versa,
e.g., the IP address of www.zyxel.com is 204.217.0.2. The DNS server is extremely important because
without it, you must know the IP address of a machine before you can access it. The DNS server addresses
that you enter in the DHCP setup are passed to the client machines along with the assigned IP address and
subnet mask.
There are two ways that an ISP disseminates the DNS server addresses. The first is for an ISP to tell a
customer the DNS server addresses, usually in the form of an information sheet, when s/he signs up. If
your ISP does give you the DNS server addresses, enter them in the DNS Server fields in DHCP Setup,
otherwise, leave them blank.
Some ISP's choose to pass the DNS servers using the DNS server extensions of PPP IPCP (IP Control
Protocol) after the connection is up. If your ISP did not give you explicit DNS servers, chances are the
DNS servers are conveyed through IPCP negotiation. The Prestige supports the IPCP DNS server
extensions through the DNS proxy feature.
If the Primary and Secondary DNS Server fields in DHCP Setup are not specified, i.e., left as 0.0.0.0, the
Prestige tells the DHCP clients that it itself is the DNS server. When a workstation sends a DNS query to
the Prestige, the Prestige forwards the query to the real DNS server learned through IPCP and relays the
response back to the workstation.
Please note that DNS proxy works only when the ISP uses the IPCP DNS server extensions. It does not
mean you can leave the DNS servers out of the DHCP setup under all circumstances. If your ISP gives you
explicit DNS servers, make sure that you enter their IP addresses in the DHCP Setup menu. This way, the
Prestige can pass the DNS servers to the workstations and the workstations can query the DNS server
directly without the Prestige's intervention.
Internet Access
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