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• 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.
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
• 172.16.0.0 — 172.31.255.255
Chapter 8 Home Networking
— 10.255.255.255
VMG8825-B Series User's Guide
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