The TED is built from information flooded by the IGP using
the traffic engineering extensions to OSPF (documented in RFC 3630) or to IS-IS
(documented in RFC 3784).
1. The computed path is encoded into an Explicit Route Object (ERO), which is
included in an RSVP-TE Path message sent toward the egress LSR (and forwarded
hop by hop to that router using IP??”but processed by the IP control
plane at each LSR).
2. Each router along the path creates state for the path and then forwards the
message toward the next router in the ERO. The ERO may contain a complete
list of the routers on the path to the egress (the usual case when using CSPF)
or may be partial or even omitted.
3. The egress LSR validates the Path message and then creates a Resv message
containing a Label Object for the LSP.
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4. The Resv message is forwarded back to the ingress LSR along the same path
followed by the Path message, using the path state at each LSR to ensure it
follows the same path. At each LSR, the label indicated in the received Label
Object will be used as the egress label for the LSP, and a new Label Object will
be included in the Resv message sent upstream to the previous LSR.
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