ZyXEL Communications VMG5313-B10A, Руководство пользователя

Страница: 153 / 398

Chapter 8 Home Networking
VMG5313-B10A/-B30A Series User’s Guide
153
8.9.3 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 DNS Server fields in
the DHCP Setup screen.
• 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 VMG supports
the IPCP DNS server extensions through the DNS proxy feature.
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.
8.9.4 LAN TCP/IP
The VMG 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 VMG.
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.
Once you have decided on the network number, pick an IP address that is easy to remember, for
instance, 192.168.1.1, for your VMG, but make sure that no other device on your network is using
that IP address.
The subnet mask specifies the network number portion of an IP address. Your VMG will compute the
subnet mask automatically based on the IP address that you entered. You don't need to change the
subnet mask computed by the VMG unless you are instructed to do otherwise.