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Label Switched Multicast (LSM) Multicast Label Distribution Protocol (mLDP) based Multicast VPN (mVPN) Support
A MP2MP LSP is similar to a P2MP LSP, but each leaf node acts as both an ingress and egress node. To
build an MP2MP LSP, you can setup a downstream path and an upstream path so that:
• Downstream path is setup just like a normal P2MP LSP
• Upstream path is setup like a P2P LSP towards the upstream router, but inherits the downstream labels
from the downstream P2MP LSP.
Packet Flow in mLDP-based Multicast VPN
For each packet coming in, MPLS creates multiple out-labels. Packets from the source network are replicated
along the path to the receiver network. The CE1 router sends out the native IP multicast traffic. The PE1 router
imposes a label on the incoming multicast packet and replicates the labeled packet towards the MPLS core
network. When the packet reaches the core router (P), the packet is replicated with the appropriate labels for
the MP2MP default MDT or the P2MP data MDT and transported to all the egress PEs. Once the packet
reaches the egress PE, the label is removed and the IP multicast packet is replicated onto the VRF interface.
Realizing a mLDP-based Multicast VPN
There are different ways a Label Switched Path (LSP) built by mLDP can be used depending on the requirement
and nature of application such as:
• P2MP LSPs for global table transit Multicast using in-band signaling.
• P2MP/MP2MP LSPs for MVPN based on MI-PMSI or Multidirectional Inclusive Provider Multicast
Service Instance (Rosen Draft).
• P2MP/MP2MP LSPs for MVPN based on MS-PMSI or Multidirectional Selective Provider Multicast
Service Instance (Partitioned E-LAN).
The Cisco CRS Router performs the following important functions for the implementation of MLDP:
1 Encapsulating VRF multicast IP packet with GRE/Label and replicating to core interfaces (imposition
node).
2 Replicating multicast label packets to different interfaces with different labels (Mid node).
3 Decapsulate and replicate label packets into VRF interfaces (Disposition node).
Characteristics of mLDP Profiles
The characteristics of various mLDP profiles are listed in this section.
Profile 1:Rosen-mLDP (with no BGP-AD)
These are the characteristics of this profile:
• MP2MP mLDP trees are used in the core.
• VPN-ID is used as the VRF distinguisher.
• Configuration based on Default MDTs.
• Same Default-MDT core-tree used for IPv4 and IPv6 traffic.
Cisco IOS XR Multicast Configuration Guide for the Cisco CRS Router, Release 5.2.x
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Implementing Multicast Routing on Cisco IOS XR Software
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