Users can disable dynamic bypass creation on a per-node basis using the config>router>mpls>dynamic-bypass command. Disabling dynamic bypass means that manual bypass is enabled. Dynamic bypass is enabled by default.
Dynamic bypass tunnels are implemented as per RFC 4090, Fast Reroute Extensions to RSVP-TE for LSP Tunnels. When an LSP is signaled and the Local Protection flag in the Session_attribute object is set, or the FRR object in the PATH message indicates that facility backup is desired, the PLR establishes a bypass tunnel to provide node and link protection. If there exists a bypass LSP that merges with the protected LSP at a downstream node, and if this LSP satisfies the constraints in the FRR object, then this bypass tunnel is selected and used. The frr-object command specifies whether facility backup is signaled in the FRR object.
The manual bypass feature allows an LSP to be preconfigured from a Point of Local Repair (PLR) that will be used exclusively for bypass protection. When a PATH message for a new LSP requests bypass protection, the node first checks for a manual bypass tunnel that satisfies the path constraints. If one is found, it is selected and used. If no manual bypass tunnel is found, the 7705 SAR dynamically signals a bypass LSP in the default behavior. To configure a manual bypass LSP, use the bypass-only option in the config>router>mpls>lsp lsp-name [bypass-only] command.
When a PLR activates a bypass backup LSP and subsequently receives a RESV refresh message for the original primary LSP path reservation over the restored interface, the PLR does not generate a ResvErr packet downstream. In addition, the MP node, once it becomes active, does not propagate a downstream ResvErr message received packet for the original primary LSP path reservation.
See Configuring Manual Bypass Tunnels for configuration information.