Service Restriction

Service restrictions can deny or allow certain Internet services access to the protected network.

For example, the Telnet service can sometimes be used by hackers to gain unauthorized access to a network. The packet filter can be programmed to drop all packets with the destination port of 23, which is the standard port for Telnet.

On the other hand, it is usually important for employees in an organization to be able to send and receive e-mail. The packet filter can be programmed to pass along all packets with the destination port of 25, which is the standard port for e-mail.