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Configuration Guide - IP Multicast

CloudEngine 12800 and 12800E V200R005C10

This document describes the configurations of IP multicast, including IP multicast basics, IGMP, MLD, PIM (IPv4), PIM (IPv6), MSDP, multicast VPN, multicast route management (IPv4), multicast route management (IPv6), IGMP snooping, MLD snooping, static multicast MAC address, multicast VLAN, multicast network management.
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Overview of Multicast VPN

Overview of Multicast VPN

Definition

Multicast virtual private network (VPN) technology allows multicast services to run on Border Gateway Protocol or Multiprotocol Label Switching (BGP/MPLS) IP VPN networks.

Multicast VPN technology encapsulates multicast packets from a private network to enable the packets to be forwarded along the multicast distribution tree (MDT) on a public network. When the packets reach the destination network, they are decapsulated and forwarded to receivers as private network multicast packets.

Purpose

Multicast VPN is used to address the following problems occurring during the multicast service deployment on the BGP/MPLS IP VPN networks:

  • VPN multicast packets cannot pass the reverse path forwarding (RPF) check on the public network.

    Different from unicast forwarding, multicast forwarding requires routers to perform RPF checks on multicast packets based on the multicast source address and inbound interface. Only multicast packets from the RPF interface are forwarded. Each router needs to know the unicast route to the multicast source. The provider (P) device on a BGP/MPLS IP VPN network does not know the VPN routes; therefore, RPF checks fail on the P device.

  • Overlapping multicast source addresses or group addresses on VPNs lead to inter-VPN communication.

    A BGP/MPLS IP VPN network allows overlapping addresses in different VPNs; therefore, the multicast source addresses or group addresses of different VPNs may overlap. A provider edge (PE) router must correctly forward multicast packets from a VPN to only the users at the sites on the same VPN to prevent communication between different VPNs.

  • If VPN packets are forwarded in unicast mode on the public network, load on the public network will increase greatly when the multicast traffic volume is high.

    The multicast technology ensures that each link transmits only one copy of multicast packets. Each router replicates multicast data according to the number of outbound interfaces, and the bandwidth consumed does not increase with the number of receivers. If the public network supports multicast forwarding, multicast packets are replicated only at bifurcation points on the public network. This on-demand replication mechanism reduces load on the public network and saves bandwidth.

  • The PE routers on a VPN can receive multicast packets from a multicast source on the same VPN. When the multicast traffic volume is high, loads on the PEs increase greatly.

    A VPN is composed of multiple sites, each of which connects to a different PE. Some sites may not have receivers. If VPN multicast data is forwarded only to the PEs with receivers connected, burdens on PEs are reduced.

Benefits

To carriers, the multicast VPN technology allows them to provide multicast services to users on VPNs. The public network does not need to know multicast data sent to users on VPNs, while VPNs do not need to know multicast routing information on the public network.

To enterprises, the multicast VPN technology allows them to deploy their own multicast on the VPNs provided by carriers. Multicast services of enterprises on different VPNs are isolated.

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Updated: 2019-04-20

Document ID: EDOC1100074724

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