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omit-no-export (Graceful Restart for BGP Helper)


Hierarchy Level


Cause the no-export BGP community to be prevented from being automatically added to routes advertised to external BGP neighbors (presumed to be CE routers). The no-export routes containing this community name are not advertised outside a BGP confederation boundary. In VPN deployments, for example, BGP is often used as a PE-CE protocol. It might be a practical necessity in such deployments to accommodate interoperation with CEs that cannot easily be upgraded to support specifications such as this one. This requirement causes a problem while ensuring that "stale" routing information does not leak beyond the perimeter of routers that support these procedures where one or more IBGP routers are not upgraded. In the VPN PE-CE case, the protocol in use is EBGP, and the LOCAL_PREF, an IBGP-only path attribute, is used.

The principal motivation for restricting the propagation of "stale" routing information is the reason to prevent it from spreading without limit once it exits the BGP confederation boundary. VPN deployments are typically topologically constrained, removing this concern. For this reason, an implementation might advertise stale routes over a PE-CE session, when explicitly configured. In such a scenario, the implementation must attach the NO_EXPORT community to the routes in question by default, as an additional protection against stale routes spreading without limit. Attachment of the NO_EXPORT community can be disabled explicitly to accommodate exceptional cases. 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 that case, if you configure the PE routers to advertise such routes, you must notify the operator of the CE receiving the routes, and the CE must be configured to depreference the routes. Typical BGP implementations perform this operation by matching on the LLGR_STALE community, and setting the LOCAL_PREF for matching routes to zero.

When the omit-no-export option is added or removed, the session is reset. This rest of a session enables LLGR stale routes to be readvertised with or without the no- export community (which is added outside of the export policy).

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.