ZyXEL Communications P-660R-D Series, User Manual

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P-660R-D Series User’s Guide
67 Chapter 5 LAN Setup
5.1.2 DHCP Setup
DHCP (Dynamic Host Configuration Protocol, RFC 2131 and RFC 2132) allows individual
clients to obtain TCP/IP configuration at start-up from a server. You can configure the ZyXEL
Device as a DHCP server or disable it. When configured as a server, the ZyXEL Device
provides the TCP/IP configuration for the clients. If you turn DHCP service off, you must
have another DHCP server on your LAN, or else the computer must be manually configured.
5.1.2.1 IP Pool Setup
The ZyXEL Device is pre-configured with a pool of IP addresses for the DHCP clients (DHCP
Pool). See the product specifications in the appendices. Do not assign static IP addresses from
the DHCP pool to your LAN computers.
5.1.3 DNS Server Address
DNS (Domain Name System) is for mapping a domain name to its corresponding IP address
and vice versa. 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 gives 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 ZyXEL Device
supports the IPCP DNS server extensions through the DNS proxy feature.
If the Primary and Secondary DNS Server fields in the DHCP Setup screen are not
specified, for instance, left as 0.0.0.0 , the ZyXEL Device tells the DHCP clients that it itself is
the DNS server. When a computer sends a DNS query to the ZyXEL Device, the ZyXEL
Device forwards the query to the real DNS server learned through IPCP and relays the
response back to the computer.
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 screen. This way, the ZyXEL Device can pass the DNS servers to the computers
and the computers can query the DNS server directly without the ZyXEL Device’s
intervention.