Policy Based Routing

Key Points

• Routes traffic by policy rules rather than destination lookup alone
• Can override default routing decisions
• Used in enterprise and carrier networks
• Supports application or source-based path selection
• Provides intentional traffic steering when standard routing is insufficient

Definition

Policy Based Routing is routing that uses rules or policies beyond the standard destination-based routing table to decide how traffic should be forwarded.

Concept

Policy Based Routing is a networking term used for forwarding decisions based on policies such as source, application, or class of traffic. It exists to provide more control than pure destination-based routing. Policy based routing allows operators to direct traffic intentionally when standard routing is not sufficient. It is used in enterprise networks, carrier environments, and specialized traffic steering designs.

Explainer

Policy Based Routing works by matching traffic against policy conditions such as source address, application, or traffic class and then selecting a forwarding path based on those rules. It is used in enterprise networks, carrier systems, and specialized traffic steering environments.

Constraints include rule ordering, route table interaction, policy conflicts, and the need to ensure that policy-based decisions do not create loops or unexpected paths. Failure modes include misrouting, inconsistent behavior, difficult troubleshooting, and policy drift if rules are not maintained carefully.

Tradeoffs involve greater forwarding control versus more complexity, policy flexibility versus harder troubleshooting, and specialized traffic handling versus a larger configuration burden. Policy Based Routing matters because not all traffic should follow the same default path in every network.