An Introduction to LANs and WANs, IP Addresses

An Introduction to LANs and WANs

Simply put, a router is a network device that connects two networks together.

The Cable Gateway has a built-in router that connects your Local Area Network (LAN), which is the group of PCs in your home or office, to the Wide Area Network (WAN), which is the Internet. The Cable Gateway processes and regulates the data that travels between these two networks.

Think of the Cable Gateway as a network device with two sides: the first side is made up of your private Local Area Network (LAN) of PCs. The other, public side, is the Internet, or the Wide Area Network (WAN), outside of your home or office.

The Cable Gateway’s firewall protects your network of PCs so users on the pub- lic, Internet side cannot “see” your PCs. This is how your local network remains private. The Cable Gateway protects your network by inspecting the first packet coming in through the WAN port before delivery to the final desti- nation in the local network. The Cable Gateway inspects Internet port services like the web server, ftp server, or other Internet applications, and, if allowed, will forward the packet to the appropriate PC on the LAN side.

IP Addresses

What’s an IP Address?

IP stands for Internet Protocol. Every device on an IP-based network, including PCs, print servers, and routers, requires an IP address to identify its “location,” or address, on the network. This applies to both the WAN and LAN connections. There are two ways of assigning an IP address to your network devices.

Static IP Addresses

A static IP address is a fixed IP address that you assign manually to a PC or other device on the network. Since a static IP address remains valid until you disable it, static IP addressing ensures that the device assigned it will always have that same IP address until you change it. Static IP addresses are com- monly used with network devices such as server PCs or print servers.

Wireless-G Cable Gateway

Dynamic IP Addresses

A dynamic IP address is automatically assigned to a device on the network, such as PCs and print servers. These IP addresses are called “dynamic” because they are only temporarily assigned to the PC or device. After a certain time period, they expire and may change. If a PC logs onto the network (or the Internet) and its dynamic IP address has expired, the DHCP server will assign it a new dynamic IP address.

DHCP (Dynamic Host Configuration Protocol) Servers

DHCP frees you from having to assign IP addresses manually every time a new user is added to your network. PCs and other network devices using dynamic IP addressing are assigned a new IP address by a DHCP server. The PC or net- work device obtaining an IP address is called the DHCP client. By default, the Cable Gateway’s WAN setting is DHCP client.

A DHCP server can either be a designated PC on the network or another net- work device, such as the Cable Gateway. By default, the Cable Gateway acts as a DHCP server for your local network. If you already have a DHCP server run- ning on your network, you must disable that DHCP server or the Cable Gateway’s DHCP’s feature. If you run more than one DHCP server on your network, you will experience network errors, such as conflicting IP addresses.

Note: Even if you assign a static IP address to a PC, other PCs can still use DHCP’s dynamic IP addressing, as long as the static IP address is not within the DHCP range of the LAN IP Address.

If the Cable Gateway’s DHCP feature fails to provide a dynamic IP address, refer to “Appendix A: Troubleshooting.”

Note: Since the Cable Gateway is a device that connects two networks, it needs two IP addresses—one for the LAN side, and one for the WAN side. In this User Guide, you’ll see references to the “WAN IP address” and the “LAN IP address.”

Since the Cable Gateway has firewall security, the only IP address on your network that can be seen from the Internet is the Cable Gateway’s WAN IP address.