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CLI-based Configuration Guide - IP Multicast

AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R007

This document describes the principles and configurations of IP multicast, and provides configuration examples.
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Inter-AS MVPN

Inter-AS MVPN

Principles

As multicast services are widely deployed and the number of users requesting multicast services is increasing, multicast users and multicast sources may reside in different ASs. To allow multicast users in a different AS to enjoy multicast services, multicast services need to be transmitted in a VPN across ASs. There are two types of inter-AS MVPNs: Option A and Option B.

NOTE:

Inter-AS MVPN does not support a switchover to the switch-MDT.

Related Concepts

The following part briefly describes the concept of inter-AS MVPN with reference to the following figures:

  • PIM Vector: refers to a technique of adding BGP neighbor information (Vector information) to PIM Join messages. Based on the Vector information, a multicast distribution tree can be established in inter-AS MVPN Option B or Option C networking. Vector information can carry Route Distinguisher (RD) information or not.

  • BGP multicast distribution tree (MDT) Subsequent Address Family Identifier (SAFI) route: refers to a route that has the same routing policy with a VPNv4 route. PEs and autonomous system boundary routers (ASBRs) check information about this route and obtain BGP neighbor information as the Vector information.

  • RD: refers to a route distinguisher, which is an eight-byte field in a VPNv4 address. A VPNv4 address is composed of an RD and a four-byte IPv4 address prefix. An RD is used to distinguish IPv4 prefixes with the same address space.

  • Inter-AS VPN Option A: refers to the networking in which ASBRs of two ASs are directly connected and are PEs (ASBR PEs) in their respective ASs, and an ASBR takes the peer ASBR as its CE and uses EBGP to advertise IPv4 routes to the peer ASBR.

  • Inter-AS VPN Option B: refers to the networking in which three independent tunnels are established between PEs and ASBRs, and between ASBRs to transmit VPN data on the public network. Data is transparently transmitted on a P in either AS so that the P does not know the route to the other AS. In addition, ASBR1 and ASBR2 only know the routes to each other, but not the route to remote PEs.

Implementation

Among three types of inter-AS MVPN, Option A supports Any-Source Multicast (ASM) and Source-Specific Multicast (SSM), whereas Option B only supports MDT-SAFI auto-discovery (A-D) of MVPN BGP A-D in SSM. The implementation of each type of inter-AS MVPN is described as follows:

  • Inter-AS MVPN Option A:

    As shown in Figure 7-17, an independent multicast domain (MD) is established in each AS, and VPN multicast data is transmitted between MDs.

    Figure 7-17  Inter-AS MVPN Option A

    In inter-AS MVPN Option A, VPN multicast data is transmitted in the following process:
    1. CE1 in VPN1 sends VPN multicast data to the CE of ASBR1", that is, ASBR2"; CE2 sends VPN multicast data to the CE of ASBR2", that is, ASBR1".

    2. After the VPN multicast data of CE1 reaches ASBR2", ASBR2" considers that the multicast data comes from VPN2. ASBR2" then encapsulates the multicast data and forwards it to PE2 and then CE2 in MD2. Similarly, VPN multicast data of CE2 can also reach CE1 based on the preceding process. In this manner, CE1 and CE2 can exchange VPN multicast data across ASs.

  • Inter-AS MVPN Option B:

    As shown in Figure 7-18, each P does not know the route to the other AS, and each ASBR does not know the route to the PE in the other AS. This hinders the establishment of a multicast distribution tree across ASs because the next hop to the multicast source cannot be identified when PIM Join messages are sent. To solve this problem, the PIM Vector technique is used. Based on PIM Vector, PEs and ASBRs check the BGP MDT SAFI route to obtain the BGP neighbor information (Vector information containing RD information), and add the Vector information to the PIM Join messages. In this manner, a multicast distribution tree can be established across ASs.

    To be specific, after receiving a PIM Join message with Vector information, a device checks whether the Vector information specifies the IP address of a local interface:

    • If the Vector information does not specify the IP address of a local interface, the device continues to send the PIM Join message to the next hop based on the Vector information.
    • If the Vector information specifies the IP address of a local interface, the device searches for the new Vector information in the BGP MDT SAFI routing table based on the RD and the multicast source IP address. If the new Vector information specifies an IP address in the same AS as the multicast source address, the device forwards the PIM Join message based on an Interior Gateway Protocol (IGP) route. If the new Vector information does not specify an IP address in the same AS as the multicast source address, the device continues to send the PIM Join message to the next hop based on the Vector information.

    In this manner, a multicast distribution tree can be established across ASs.

    Inter-AS MVPN Option B needs only one MD to be established across ASs.

    Figure 7-18  Inter-AS MVPN Option B

    In inter-AS MVPN Option B, VPN multicast data is transmitted in the following process:
    1. VPN multicast data of CE1 is encapsulated on PE1 based on MTI and then forwarded over Multicast Tunnel (MT) tunnels. The encapsulated VPN multicast data is transmitted over the public network as common multicast data based on Share-Group or Switch-Group entries of the public network.

    2. The VPN multicast data reaches PE2 and inter-AS multicast is implemented. PE1 and PE2 do not know how VPN multicast data is transmitted across ASs and consider that the VPN multicast data is transmitted within the same AS.

Application scenario

Inter-AS MVPN is applicable to networks that adopt inter-AS VPN Option A and Option B.

Advantages

Inter-AS MVPN allows carriers to deploy multicast VPN across ASs to provide multicast services for users in different ASs.

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Updated: 2019-06-12

Document ID: EDOC1000097181

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