MVPN allows a service provider to configure and support multicast traffic in an MPLS VPN environment. This type supports routing
and forwarding of multicast packets for each individual VPN routing and forwarding (VRF) instance, and it also provides a
mechanism to transport VPN multicast packets across the service provider backbone. In the MLDP case, the regular label switch
path forwarding is used, so core does not need to run PIM protocol. In this scenario, the c-packets are encapsulated in the
MPLS labels and forwarding is based on the MPLS Label Switched Paths (LSPs).
The MVPN mLDP service allows you to build a Protocol Independent Multicast (PIM) domain that has sources and receivers located
in different sites.
To provide Layer 3 multicast services to customers with multiple distributed sites, service providers look for a secure and
scalable mechanism to transmit customer multicast traffic across the provider network. Multicast VPN (MVPN) provides such
services over a shared service provider backbone, using native multicast technology similar to BGP/MPLS VPN.
MVPN emulates MPLS VPN technology in its adoption of the multicast domain (MD) concept, in which provider edge (PE) routers
establish virtual PIM neighbor connections with other PE routers that are connected to the same customer VPN. These PE routers
thereby form a secure, virtual multicast domain over the provider network. Multicast traffic is then transmitted across the
core network from one site to another, as if the traffic were going through a dedicated provider network.
Separate multicast routing and forwarding tables are maintained for each VPN routing and forwarding (VRF) instance, with traffic
being sent through VPN tunnels across the service provider backbone.
In the Rosen MVPN mLDP solution, a multipoint-to-multipoint (MP2MP) default MDT is setup to carry control plane and data traffic.
A disadvantage with this solution is that all PE routers that are part of the MVPN need to join this default MDT tree. Setting
up a MP2MP tree between all PE routers of a MVPN is equivalent to creating N P2MP trees rooted at each PE (Where N is the
number of PE routers). In an Inter-AS (Option A) solution this problem is exacerbated since all PE routers across all AS’es
need to join the default MDT. Another disadvantage of this solution is that any packet sent through a default MDT reaches
all the PE routers even if there is no requirement.
In the partitioned MDT approach, only those egress PE routers that receive traffic requests from a particular ingress PE join
the PMSI configured at that ingress PE. This makes the number of ingress PE routers in a network to be low resulting in a
limited number of trees in the core.
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