forwarding-state-bit (Per Family for BGP Graceful Restart)

Syntax

Hierarchy Level

Description

Configure the forwarding-state bit flag negotiation for BGP for individual address families. In addition to the global setting for the Forwarding State bit, the Forwarding State bit behavior can be specified for individual families. Changing the forwarding-state-bit setting has no effect on any existing sessions. Per-family BGP configuration options are added to control the Forwarding State bit in graceful restart and long-lived graceful restart capability advertisements. They can be specified for the default logical system or for a specific logical system, and for the primary routing instance or a specific routing instance. The per-family forwarding-state-bit attribute overrides the default rules or the global configuration for setting the Forwarding State bit.

The setting of the F bit (and the "Forwarding State" bit of the accompanying GR capability) depends in part on deployment considerations. The F bit can be interpreted to indicate the helper router needs to flush associated routes (if the bit is left clear). An important scenario in which LLGR is used is for routes that are more similar to configuration than to traditional routing (hop-by-hop forwarding instead of tunnel-based routing). For such routes, it might be useful to always set the F bit, regardless of other considerations. Similarly, for control-plane-only entities such as dedicated route reflectors, that do not participate in the forwarding plane, it is preferred that the F bit be always set. Overall, the guideline to be adopted is that if loss of state on the restarting router can reasonably be expected to cause a forwarding loop or null route, the F bit must be set judiciously, depending on whether state has been retained. You can determine whether the F bit needs to be set or not, based on your deployment needs and configured settings. It might be necessary to advertise stale routes to a CE in some VPN deployments, even if the CE does not support this specification. In such a scenario, the network operator configuring their PE to advertise such routes must notify the operator of the CE receiving the routes, and the CE must be configured to depreference the routes. Typically, BGP implementations perform this behavior by matching on the LLGR_STALE community, and setting the LOCAL_PREF for matching routes to zero.

Options

Required Privilege Level

routing—To view this statement in the configuration.

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

Release Information

Statement introduced in Junos OS Release 15.1.