Mar 10, 2013

MPLS Point-to-Multipoint Traffic Engineering


Prerequisites for MPLS Point-to-Multipoint Traffic Engineering

Before configuring the MPLS Point-to-Multipoint Traffic Engineering (P2MP TE) feature, note the
following:

  • Configure Resource Reservation Protocol (RSVP) and traffic engineering features on the headend, midpoint, and tailend routers in the MPLS network. 
  • Cisco nonstop NSF/SSO is supported only on platforms with dual Route Processors on which NSF/SSO is configured.
  • For NSF/SSO support, all routers (headend, midpoint, and tailend) must be Cisco 7600 series routers.
  • All routers must be configured for RSVP graceful restart. For more information, see NSF/SSO—MPLS TE and RSVP Graceful Restart. 


MPLS Point-to-Multipoint Traffic Engineering Overview

A P2MP TE network contains the following elements, which are shown in Figure 1:

  • The headend router, also called the source or ingress router, is where the label switched path (LSP) is initiated. The headend router can also be a branch point, which means the router performs packet replication and the sub-LSPs split into different directions.
  • The midpoint router is where the sub-LSP signaling is processed. The midpoint router can be a branch point. 
  • The tailend router, also called the destination, egress, or leaf-node router, is where sub-LSP signaling ends. 
  • A bud router is a midpoint and tailend router at the same time.
  • A P2MP tunnel consists of one or more sub-LSPs. All sub-LSPs belonging to the same P2MP tunnel employ the same constraints, protection policies, and so on, which are configured at the headend router.



P2MP TE tunnels build on the features that exist in basic point-to-point TE tunnels. The P2MP TE
tunnels have the following characteristics:

  • There is one source (headend) but more than one destination (tailend).
  • They are unidirectional.
  • They are explicitly routed.
  • Multiple sub-LSPs connect the headend router to various tailend routers.


Figure 2 shows a P2MP TE tunnel that has three destinations.

  • PE1 is the headend router.
  • P01 is a branch point router, where packet replication occurs.
  • PE2, PE3, and PE4 are tailend routers, where the sub-LSP ends. 

Between the PE and CE routers, PIM is enabled to exchange multicast routing information with the
directly connected customer edge (CE) routers. PIM is not enabled across the P2MP TE tunnel.




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