NETGEAR CG814WG manual Single IP Address Operation Using NAT

Hardware Manual for the Model CG814WG Wireless Cable Modem Gateway

Table D-2. Netmask Formats

255.255.255.0 /24

255.255.255.128 /25

255.255.255.192 /26

255.255.255.224 /27

255.255.255.240 /28

255.255.255.248 /29

255.255.255.252 /30

255.255.255.254 /31

255.255.255.255 /32

NETGEAR strongly recommends that you configure all hosts on a LAN segment to use the same netmask for the following reasons:

•So that hosts recognize local IP broadcast packets

When a device broadcasts to its segment neighbors, it uses a destination address of the local network address with all ones for the host address. In order for this scheme to work, all devices on the segment must agree on which bits comprise the host address.

•So that a local router or bridge recognizes which addresses are local and which are remote

Single IP Address Operation Using NAT

In the past, if multiple PCs on a LAN needed to access the Internet simultaneously, you had to obtain a range of IP addresses from the ISP. This type of Internet account is more costly than a single-address account typically used by a single user with a modem, rather than a router. The CG814WG Gateway employs an address-sharing method called Network Address Translation (NAT). This method allows several networked PCs to share an Internet account using only a single IP address, which may be statically or dynamically assigned by your ISP.

The router accomplishes this address sharing by translating the internal LAN IP addresses to a single address that is globally unique on the Internet. The internal LAN IP addresses can be either private addresses or registered addresses. For more information about IP address translation, refer to RFC 1631, The IP Network Address Translator (NAT).

The following figure illustrates a single IP address operation.

Networks, Routing, and Firewall Basics D-7