The packet filter then redirects the connection to the web-proxy which can perform detailed filtering on the website without having to pass through all unfiltered connections.

For several years computer security specialists have used software variously known as packet filters, or "sniffers," as monitoring devices to track computer intruders.

Investigators often only have material to examine if packet filters, firewalls, and intrusion detection systems were set up to anticipate breaches of security.

Firewalls built on pure packet filters cannot reject some "stealth scans" very well.

But simple packet filters, they're not concerned at all about the content of the packet.

And so early packet filters, where you didn't want to allow incoming connections, all they did - they were sort of dumb.

It is rare to find application firewalls not combined or used in conjunction with a packet filter.

This newer ipchains was required to manage the packet filter in Linux kernels starting with version 2.1.102 (which was a 2.2 development release).

With the advanced packet filter, rules can also be specified for source and destination IP addresses and port ranges.

These approaches all have severe performance disadvantages for code as frequently run as a packet filter.