Crlsp Establishment Using Pce Path Calculation - HP FlexNetwork 10500 Series Configuration Manual

Explicit path specifies the nodes to pass and the nodes to not pass for a tunnel.
Explicit paths include the following types:
Strict explicit path—Among the nodes that the path must traverse, a node and its previous

hop must be directly connected. Strict explicit path precisely specifies the path that an
MPLS TE tunnel must traverse.
Loose explicit path—Among the nodes that the path must traverse, a node and its

previous hop can be indirectly connected. Loose explicit path vaguely specifies the path that
an MPLS TE tunnel must traverse.
Strict explicit path and loose explicit path can be used together to specify that some nodes are
directly connected and some nodes have other nodes in between.
Setting up a CRLSP through RSVP-TE
After calculating a path by using CSPF, MPLS TE uses a label distribution protocol to set up the
CRLSP and reserves resources on each node of the path.
The device supports the label distribution protocol of RSVP-TE for MPLS TE. Resource Reservation
Protocol (RSVP) reserves resources on each node along a path. Extended RSVP can support MPLS
label distribution and allow resource reservation information to be transmitted with label bindings.
This extended RSVP is called RSVP-TE.
For more information about RSVP, see

CRLSP establishment using PCE path calculation

On an MPLS TE network, a Path Computation Client (PCC), usually an LSR, uses the path
calculated by Path Computation Elements (PCEs) to establish a CRLSP through RSVP-TE.
Basic concepts
•
PCE—An entity that can calculate a path based on the TEDB, bandwidth, and other MPLS TE
tunnel constraints. A PCE can provide intra-area or inter-area path calculation. A PCE can be
manually specified on a PCC or automatically discovered through the PCE information
advertised by OSPF TE.
•
PCC—A PCC sends a request to PCEs for path calculation and uses the path information
returned by PCEs to establish a CRLSP.
•
PCEP—Path Computation Element Communication Protocol. PCEP runs between a PCC and
a PCE, or between PCEs. It is used to establish PCEP sessions to exchange PCEP messages
over TCP connections.
PCE path calculation
PCE path calculation has the following types:
•
EPC—External Path Computation. EPC path calculation is performed by one PCE. It is
applicable to intra-area path calculation.
•
BRPC—Backward-Recursive PCE-Based Computation. BRPC path calculation is performed
by multiple PCEs. It is applicable to inter-area path calculation.
As shown in
ABR that can calculate paths in Area 1 and Area 2. The CRLSP that PCC uses to reach a destination
in Area 2 is established as follows:
1. PCC sends a path calculation request to PCE 1 to request the path to the CRLSP destination.
2. PCE 1 forwards the request to PCE 2.
PCE 1 cannot calculate paths in Area 2, so it forwards the request to PCE 2, the PCE
responsible for Area 2 that contains the CRLSP destination.
3. After receiving the request from PCE 1, PCE 2 calculates potential paths to the CRLSP
destination and sends the path information back to PCE 1 in a reply.
Figure 25, PCE 1 is the ABR that can calculate paths in Area 0 and Area 1. PCE 2 is the
"Configuring RSVP."
74