One of the reasons that people buy a router, aside from sharing their Internet connection, is to protect their LAN computers from Internet-based attacks.\u00a0 The primary means of protection is the firewall function that a router or proxy provides. <\/p>\n\n\n\n
The\u00a0ICSA Firewall Buyers Guide<\/b>\u00a0provides a good definition:
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Put simply, a firewall is a mechanism used to protect a trusted network from an untrusted network, usually while still allowing traffic between the two.<\/cite><\/p>\n\n\n\n There are many ways to implement a firewall, but the most popular for both hardware and software routers is\u00a0Network Address Translation<\/b>\u00a0or\u00a0NAT<\/b>.\u00a0 <\/p>\n\n\n\n Most inexpensive routers use NAT as the means to share one IP address among many computers.\u00a0\u00a0 <\/p>\n\n\n\n NAT also provides a natural firewall that will protect the computers behind it from access by unauthorized users.\u00a0\u00a0<\/p>\n\n\n\n How?\u00a0 <\/p>\n\n\n\n NAT automatically provides firewall-style protection without any special set-up. That is because it only allows connections that are originated on the inside network. <\/cite><\/p>NAT automatically provides firewall-style protection without any special set-up. That is because it only allows connections that are originated on the inside network. <\/cite><\/blockquote>\n\n\n\n This means, for example, that an internal client can connect to an outside FTP server, but an outside client will not be able to connect to an internal FTP server because it would have to originate the connection, and NAT will not allow that. <\/cite><\/p>\n\n\n\n