The multicast virtual private networks (MVPNs) feature allows you to support multicast connectivity over Layer 3 VPN. IP multicast is used to stream video, voice, and data to an VPN network core.
Historically, point-to-point tunnels were the only way to connect through an enterprise or service provider network. Although such tunneled networks had scalability issues, they were the only means of passing IP multicast traffic through a virtual private network (VPN). Because Layer 3 VPNs support only unicast traffic connectivity, deploying with a Layer 3 VPN allows operators to offer both unicast and multicast connectivity to Layer 3 VPN customers
MVPNs allows you to configure and support multicast traffic in an MVPN environment. MVPNs support routing and forwarding of multicast packets for each individual virtual routing and forwarding (VRF) instance, and it also provides a mechanism to transport VPN multicast packets across the enterprise or service provider backbone. IP multicast is used to stream video, voice, and data to a VPN network core.
A VPN allows network connectivity across a shared infrastructure, such as an Internet Service Provider (ISP). Its function is to provide the same policies and performance as a private network at a reduced cost of ownership.
MVPNs allow an enterprise to transparently interconnect its private network across the network backbone. Using MVPNs to interconnect an enterprise network does not change the way that an enterprise network is administered and it does not change general enterprise connectivity.
MVPN Routing and Forwarding and Multicast Domains
MVPNs introduce multicast routing information to the VPN routing and forwarding table. When a provider edge (PE) router receives multicast data or control packets from a customer edge (CE) router, the router forwards the data or control packets according to the information in the MVPN routing and forwarding (MVRF).
A set of MVRFs that can send multicast traffic to each other constitutes a multicast domain. For example, the multicast domain for a customer that wanted to send certain types of multicast traffic to all global employees would consist of all CE routers that are associated with that enterprise.
Multicast Distribution Trees
MVPNs establish a static default multicast distribution tree (MDT) for each multicast domain. The default MDT defines the path used by PE routers to send multicast data and control messages to every other PE router in the multicast domain.
MVPNs also support the dynamic creation of MDTs for high-bandwidth transmission. Data MDTs are intended for high-bandwidth sources such as full-motion video inside the VPN to ensure optimal traffic forwarding in the VPN core.
In the following example, a service provider has a multicast customer with offices in San Jose, New York, and Dallas. A one-way multicast presentation is occurring in San Jose. The service provider network supports all three sites that are associated with this customer, in addition to the Houston site of a different enterprise customer. The default MDT for the enterprise customer consists of provider routers P1, P2, and P3 and their associated PE routers. PE4 is not part of the default MDT, because it is associated with a different customer. The following figure shows that no data flows along the default MDT, because no one outside of San Jose has joined the multicast.
An employee in New York joins the multicast session. The PE router that is associated with the New York site sends a join request that flows across the default MDT for the multicast domain of the customer. PE1, the PE router that is associated with the multicast session source, receives the request. The following figure depicts that the PE router forwards the request to the CE router that is associated with the multicast source (CE1a).
The CE router (CE1a) begins to send the multicast data to the associated PE router (PE1), which sends the multicast data along the default MDT. PE1 creates a data MDT, sends a message to all routers using the default MDT that contains information about the data MDT, and, three seconds later, begins sending the multicast data for that particular stream using the data MDT. Only PE2 has interested receivers for this source, so only PE2 joins the data MDT and receives traffic on it. (If the data MDT had not been configured and only the default MDT had been configured, all the customer sites would have received the traffic even though they were not interested in it.) PE routers maintain a PIM relationship with other PE routers over the default MDT and a PIM relationship with its directly attached P routers.
Multicast Tunnel Interface
An MVPN routing and forwarding (MVRF), which is created per multicast domain, requires the router to create a tunnel interface from which all MVRF traffic is sourced. A multicast tunnel interface is an interface that the MVRF uses to access the multicast domain. The interface is a conduit that connects an MVRF and the global MVRF. One tunnel interface is created per MVRF.
Benefits of MVPNs
The benefits of MVPNs are as follows:
Provides a scalable method to dynamically send information to multiple locations.
Provides high-speed information delivery.
Provides connectivity through a shared infrastructure.