out-delay

Syntax

Hierarchy Level

Description

Control how often BGP and the routing table exchange route information by specifying how long a route must be present in the Junos OS routing table before it is exported to BGP. Use this time delay to help bundle routing updates and to avoid sending updates too often.

Alternatively or in addition, external BGP (EBGP) sessions can also use the route-flap damping mechanism upon the reception of BGP messages coming from an external neighbor.

BGP stores the route information it receives from update messages in the routing table, and the routing table exports active routes from the routing table into BGP. BGP then advertises the exported routes to its peers. The out-delay statement enables a form of rate limiting. The delay is added to each update for each prefix individually. When a routing device changes its best path to a destination prefix, the device does not inform its peer about the change unless the route has been present in its routing table for the specified out-delay. If you use out-delay to perform rate-limiting, you can expect a less bursty pattern of updates. You will see a pattern in which updates arrive in a steady flow, and two updates for the same prefix are always spaced by at least the out-delay timer value (for example, 30 seconds). Thus, the out-delay setting is useful for limiting oscillation (sometimes called churn) in a network. Keep in mind that, regardless of the out-delay setting, BGP peers exchange routes immediately after neighbor establishment. The out-delay setting is only designed to delay the exchange of routes between BGP and the local routing table.

Caution is warranted because an out-delay can delay convergence. If your network is configured in a way that avoids oscillation, setting an out-delay is not necessary.

When configured, the out-delay value displays as Outbound Timer when using show bgp group or show bgp group neighbor commands.

Default

By default, the exchange of route information between BGP and the routing table occurs immediately after the routes are received. This immediate exchange of route information might cause instabilities in the network reachability information. If you omit this statement, routes are exported to BGP immediately after they have been added to the routing table.

Options

seconds—Output delay time.

• Range: 0 through 65,535 seconds

• Default: 0 seconds

Required Privilege Level

routing—To view this statement in the configuration.

routing-control—To add this statement to the configuration.

Release Information

Statement introduced before Junos OS Release 7.4.