ZyXEL Communications P-660RU-T1 v3, Руководство пользователя, Страница: 78 / 230

Chapter 8 LAN Setup
P-660RU-Tx v3 User’s Guide
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8.3.3 DNS Server Addresses
DNS (Domain Name System) maps 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. The DNS server addresses you enter when you
set up DHCP 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 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 Primary
and Secondary DNS Server fields.
• Some ISPs choose to disseminate the DNS server addresses using the DNS server
extensions of 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 DHCP is
set to Relay , 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 acts as a DNS proxy and 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.
8.3.4 LAN TCP/IP
The ZyXEL Device has built-in DHCP server capability that assigns IP addresses and DNS
servers to systems that support DHCP client capability.
IP Address and Subnet Mask
Similar to the way houses on a street share a common street name, so too do computers on a
LAN share one common network number.
Where you obtain your network number depends on your particular situation. If the ISP or
your network administrator assigns you a block of registered IP addresses, follow their
instructions in selecting the IP addresses and the subnet mask.
If the ISP did not explicitly give you an IP network number, then most likely you have a single
user account and the ISP will assign you a dynamic IP address when the connection is
established. If this is the case, it is recommended that you select a network number from
192.168.0.0 to 192.168.255.0 and you must enable the Network Address Translation (NAT)
feature of the ZyXEL Device. The Internet Assigned Number Authority (IANA) reserved this
block of addresses specifically for private use; please do not use any other number unless you
are told otherwise. Let's say you select 192.168.1.0 as the network number; which covers 254
individual addresses, from 192.168.1.1 to 192.168.1.254 (zero and 255 are reserved). In other
words, the first three numbers specify the network number while the last number identifies an
individual computer on that network.