Lan Tcp/Ip - ZyXEL Communications P-793H v3 User Manual

• 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 P-79X
supports the IPCP DNS server extensions through the DNS proxy feature.
If the DNS Server fields in the DHCP Setup screen are set to DNS Relay, the P-79X tells the
DHCP clients that it itself is the DNS server. When a computer sends a DNS query to the P-79X,
the P-79X 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 in the
DHCP Setup screen.

8.6.4 LAN TCP/IP

The P-79X 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 P-79X.
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 P-79X, 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 P-79X 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 P-79X unless you are instructed to do otherwise.
Private IP Addresses
Every machine on the Internet must have a unique address. If your networks are isolated from the
Internet, for example, only between your two branch offices, you can assign any IP addresses to
the hosts without problems. However, the Internet Assigned Numbers Authority (IANA) has
reserved the following three blocks of IP addresses specifically for private networks:
• 10.0.0.0
Chapter 8 LAN Setup
— 10.255.255.255
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