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[Part 5 of 7]

Cable Modem Security Issues

Plugging a cable modem into an Ethernet hub makes your local network part of a larger network that includes all your neighbors who also have cable modem connections. Without some protection on your end, those neighbors could potentially access shared files on your computers, and you might be able to access your neighbors' shared files as well. You can protect against this security risk in several ways. For one, you can lock neighbors out of your shared folders and disks by requiring a password to connect to a shared item.

For more protection, you can install a gateway with a firewall that can be set up to filter out file sharing that uses the TCP/IP protocol.

Dual Ethernet improves security

You can provide additional security by plugging the cable modem directly into an Internet gateway that has two Ethernet ports. Your network hub connects to one port, and the cable modem connects to the other. This dual-Ethernet gateway can be a hardware box with two Ethernet ports, or a software gateway running on a computer with two Ethernet ports. The gateway provides a path between the ports for Internet traffic and other TCP/IP traffic but does not provide a path for traffic that uses other protocols used for file and printer sharing, such as the NetBEUI protocol, which PCs can use, or the AppleTalk protocol, which most Macs use.

Warning to DHCP users: If your Internet gateway has only one Ethernet port, make sure you don't have a DHCP (Dynamic Host Configuration Protocol) server running on your local network. If your gateway has this feature, don't activate it. If you do, your DHCP server might try to supply IP addresses to all of the computers on the network--including your neighbors' machines!

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