SR OS implements dynamic bypass tunnels as defined in RFC 4090, Fast Reroute Extensions to RSVP-TE for LSP Tunnels. When an LSP is signaled and the local protection flag is set in the session_attribute object or the FRR object in the path message indicates that facility backup is needed, the PLR establishes a bypass tunnel to provide node and link protection. The bypass tunnel is selected if a bypass LSP that merges in a downstream node with the protected LSP exists, and if this LSP satisfies the constraints in the FRR object.
With the manual bypass feature, an LSP can be preconfigured from a PLR that is used exclusively for bypass protection. When a Path message for a new LSP requests bypass protection, the node first checks if a manual bypass tunnel satisfying the path constraints exists. If one is found, it is selected. If no manual bypass tunnel is found, the router dynamically signals a bypass LSP in the default behavior. Users can disable the dynamic bypass creation on a per node basis using the CLI.
A maximum of 1000 associations of primary LSP paths can be made with a single manual bypass by default. The max-bypass-associations integer command allows to increase or decrease the number of associations. If dynamic bypass creation is disabled on the node, it is recommended to configure additional manual bypass LSPs to handle the required number of associations.
See Configuring Manual Bypass Tunnels for configuration information.