Egress Filtering

What Does Egress Filtering Mean?

Egress filtering is a network security measure that filters outgoing data using a firewall before transmitting the data to another network, preventing all unauthorized traffic from leaving the network.


If a data packet fails to meet the security requirements set by a firewall, it is blocked from leaving the network. This is usually practiced in highly private networks with private TCP/IP computers that contain sensitive or confidential information.

Egress filtering is the opposite of ingress filtering, which blocks selected outside traffic from getting inside the network.

Techopedia Explains Egress Filtering

The main purpose of egress filtering is to trap potentially malicious software and events, such as viruses and service attacks, from infecting neighboring networks.

Trapping keeps harmful programs, email messages and website requests from leaving a network. Some organizations use this filtering technique to control the release of internal information to keep their data and system secure, even invisible, from potential hackers and crackers.

Egress filtering has two processes: monitoring and setting requirements.

  • Monitoring includes watching and recording outbound information that is transmitted through the network.

  • Setting determines which data is allowed to go out and which is blocked.

The processes are usually determined during the establishment of the main system. Combined with other measures, egress filtering helps create overall network security.


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Margaret Rouse

Margaret Rouse is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical, business audience. Over the past twenty years her explanations have appeared on TechTarget websites and she's been cited as an authority in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine and Discovery Magazine.Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages. If you have a suggestion for a new definition or how to improve a technical explanation, please email Margaret or contact her…