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ME60 V800R010C10SPC500 Feature Description - IP Multicast 01

This is ME60 V800R010C10SPC500 Feature Description - IP Multicast
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BGP A-D MVPN

BGP A-D MVPN

Background

Multicast packets, including protocol packets and data packets, are transmitted from the public network to a private network along a public network multicast distribution tree (MDT). Public network MDTs are categorized into the following types:
  • PIM-SM MDT: an MDT established by sending PIM-SM Join messages to the intermediate device RP. PIM-SM MDTs are used in scenarios in which the location of the multicast source (multicast tunnel interface) is unknown.
  • PIM-SSM MDT: an MDT established by sending PIM-SSM Join messages to the multicast source. PIM-SSM MDTs are used in scenarios in which the location of the multicast source (multicast tunnel interface) is known.

Before the BGP A-D MVPN is introduced, MD MVPNs can establish only PIM-SM MDTs. This is because PEs belonging to the same VPN cannot detect each other's peer information. As a result, PEs belonging to the same VPN cannot detect the multicast source, and therefore are unable to send PIM-SSM Join messages to the multicast source to establish a PIM-SSM MDT.

After the BGP A-D MVPN is introduced, MD MVPNs can also establish PIM-SSM MDTs. On a BGP A-D MVPN, PEs obtain and record peer information about a VPN by exchanging BGP Update packets that carry A-D route information. Then, these PEs send PIM-SSM Join messages directly to the multicast source to establish a PIM-SSM MDT. After the PIM-SSM MDT is established, the BGP A-D MVPN transmits multicast services over a public network tunnel based on the PIM-SSM MDT.

Related Concepts

The concepts related to BGP A-D MVPN are as follows:
  • MD MVPN: See MVPN Terms.

  • Peer: a BGP speaker that exchanges messages with another BGP speaker.

  • BGP A-D: a mechanism in which PEs exchange BGP Update packets that carry A-D route information to obtain and record peer information of a VPN.

Implementation

For multicast VPN in BGP A-D mode, only MDT-SAFI A-D is supported, in which a new address family is defined by BGP. In this manner, after VPN instance is configured on a PE, the PE advertises the VPN configuration including the RD, share-group address, and IP address of the MTI interface to all its BGP peers. After a remote PE receives an MDT-SAFI message advertised by BGP, the remote PE compares the Share-Group address in the message with its Share-Group address. If the remote PE confirms that it is in the same VPN as the sender of the MDT-SAFI message, the remote PE establishes the PIM-SSM MDT on the public network to transmit multicast VPN services.

Figure 7-14 Networking diagram of multicast VPN in BGP A-D mode

As shown in Figure 7-14, PE1, PE2, and PE3 belong to VPN1, and join the share-group G1. The address of G1 is within the SSM group address range. BGP MDT-SAFI A-D mode is enabled on each PE. In addition, the BGP A-D function is enabled on VPN1. The site where CE1 resides is connected to Source of VPN1, and CE2 and CE3 are connected to VPN1 users. Based on the BGP A-D mechanism, every PE on the network obtains and records information about all its BGP peers on the same VPN, and then directly establishes a PIM-SSM MDT on the public network for transmitting multicast VPN services. In this manner, MVPN services can be transmitted over a public network tunnel based on the PIM-SSM MDT.

The following uses PE3 as an example to describe service processing in MVPN in BGP A-D mode:
  1. After being configured with the BGP A-D function, PE1, PE2, and PE3 negotiate session parameters, and confirm that both ends support the BGP A-D function. Then, the PEs can establish BGP peer relationships. After receiving a BGP Update packet from PE1 and PE2, respectively, PE3 obtains and records the BGP peer addresses of PE1 and PE2. The BGP Update packets carry the information about the PEs that send packets, such as the PE address and supported tunnel type.

  2. VPN1 is configured on PE3. PE3 joins the share-group G1. PE3 creates a PIM-SSM entry with G1 being the group address and the address of PE1 being the source address and another PIM-SSM entry with G1 being the group address and the address of PE2 being the source address. PE3 then directly sends PIM Join messages to PE1 and PE2 to establish two PIM-SSM MDTs to PE1 and PE2, respectively.

  3. CE3 sends a Join message to PE3. After receiving the Join message, PE3 encapsulates the Join message with the PIM-SSM share-group address, and then sends it to PE1 over the public network tunnel. PE1 then decapsulates the received Join message, and then sends it to the multicast source.

  4. After the multicast data sent by the multicast source reaches PE1, PE1 encapsulates the multicast data with the share-group address, and then forwards it to PE3 over the public network tunnel. PE3 then forwards the multicast data to CE3, and CE3 sends the multicast data to the user.

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Updated: 2019-01-04

Document ID: EDOC1100059456

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