Routing policies

The SR Linux supports policy-based routing. Policy-based routing controls the size and content of the routing tables, the routes that are advertised, and the best route to take to reach a destination.

Each routing policy has a sequence of rules (called entries or statements) and a default action. Each statement has numerical sequence identifier that determines its order relative to other statements in that policy. The statement supports both alphanumerical and numerical sequence identifiers. When a route is analyzed by a policy, it is evaluated by each statement in sequential order.

Each policy statement has zero or more match conditions and a base action (either accept or reject); the statement may also have route-modifying actions. A route matches a statement if it meets all of the specified match conditions.

The first statement that matches the route determines the actions that are applied to the route. If the route is not matched by any statements, the default action of the policy is applied. If there is no default action, then a protocol- and context-specific default action is applied.

All routes match a statement with no match conditions. When a route fulfills the match conditions of a statement, the base action of the statement is applied, along with all of its route-modifying actions.