Establishing RSVP-TE LSPs

Establishing LSPs requires every LSR along the path to support RSVP and the TE extensions defined in RFC 3209.

The LSP endpoints attempt to detect non-RSVP capable LSRs by comparing the time-to-live (TTL) value maintained in the RSVP common header with that of the IP TTL. If these values are different, it is assumed that a non-RSVP capable LSR exists along the path. By including the Label Request object in the path message, RSVP capable routers that do not support the TE extensions can be detected. RSVP routers that do not support TE extensions reply with the Unknown object class error.

RSVP-TE LSPs are referred to as named LSPs. These LSPs have configurable names that are used to identify the LSP within the CLI. The command create mpls rsvp-te lsp lsp_name destination ipaddress allocates the internal resources for the LSP. The newly created LSP is not signaled until the LSP has been configured. The LSP can be configured to take a specific path through the network or the administrator can let the switch choose the best path by specifying the path any. Up to three paths may be configured for an LSP to provide redundancy. The command configure mpls rsvp-te lsp lsp_name add path configures an LSP. Optionally, RSVP-TE profiles may be applied to an LSP to change its properties. An RSVP-TE profile is a specific CLI container used to hold configuration parameters associated with timers, bandwidth reservation, limits, and other miscellaneous properties.

Once the RSVP-TE LSP is configured, the LSP is immediately signaled. If signaled successfully, the LSP becomes active. The commands disable mpls rsvp-te lsp lsp_name and enable mpls rsvp-te lsp lsp_name are used to tear down and re-signal the LSP. Disabling the LSP causes the LER to send a path tear message to the destination, forcing the LSP down and all resources along the path to be freed. Enabling the LSP instructs the LER to send a path message to the destination re-establishing the LSP. The configuration of the LSP is not modified by the enable or disable LSP commands.