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P-660R-Tx v2 Series User’s Guide
49 Chapter 5 LAN Setup
5.2 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 the LAN Setup screen, 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 LAN 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
LAN 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.
5.3 DNS Server Address Assignment
Use DNS (Domain Name System) to map 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 computer before you can access it.
There are two ways that an ISP disseminates the DNS server addresses.
• The ISP tells you the DNS server addresses, usually in the form of an information sheet,
when you sign up. If your ISP gives you DNS server addresses, enter them in the DNS
Server fields in the LAN Setup screen.
• The ZyXEL Device acts as a DNS proxy when the Primary and Secondary DNS Server
fields are left blank in the LAN Setup screen.