NG MVPN Public Network Tunnel Principle

NG MVPN devices exchange routing information through BGP and establishes an MVPN tunnel based on MPLS P2MP to carry multicast traffic.

The establishment of NG MVPN tunnels is affected by the network deployed on the public network, including whether the public network contains multiple ASs and whether different MPLS protocols are deployed in different areas. According to the two factors, NG MVPN deployment scenarios can be classified into the following types:
  • Intra-AS non-segmented NG MVPN: The public network contains only one AS, and only one MPLS protocol is deployed.
  • Intra-AS segmented NG MVPN: The public network contains only one AS but contains multiple areas. Different MPLS protocols are deployed in adjacent areas.
  • Inter-AS non-segmented NG MVPN: The public network contains multiple ASs, and only one MPLS protocol is deployed in the ASs.

For details about the NG MVPN deployment scenarios, see NG MVPN Typical Deployment Scenarios on the Public Network.

Tunnel establishment includes the following basic steps and slightly differs in different scenarios:

  1. MVPN membership autodiscovery

    MVPN membership autodiscovery is a process that automatically discovers MVPN peers and establishes MVPN peer relationships. A sender PE and a receiver PE on the same MVPN can exchange control messages that carry MVPN NLRI to establish a PMSI tunnel only after they establish an MVPN peer relationship. In NetEngine 8000 F, PEs use BGP as the signaling protocol to exchange control messages.

  2. I-PMSI tunnel establishment

    PMSI tunnels are logical tunnels used by a public network to transmit VPN multicast traffic.

  3. Switching between I-PMSI and S-PMSI tunnels

    After switching between I-PMSI and S-PMSI tunnels is configured, if the multicast data forwarding rate exceeds the switching threshold, multicast data is switched from the I-PMSI tunnel to an S-PMSI tunnel. Unlike the I-PMSI tunnel that sends multicast data to all PEs on an NG MVPN, an S-PMSI tunnel sends multicast data only to PEs interested in the data, reducing bandwidth consumption and PEs' burdens.

  4. Transmitting multicast traffic on an NG MVPN

    After a public network PMSI tunnel is created, multicast users can join the multicast group and apply for multicast services from the multicast source. The multicast source can send multicast traffic to multicast users through the PMSI tunnel.

The concepts and protocols related to the multicast traffic carried by the public network tunnel are as follows:

PMSI Tunnel

Public tunnels (P-tunnels) are transport mechanisms used to forward VPN multicast traffic across service provider networks. In NetEngine 8000 F, PMSI tunnels can be carried over RSVP-TE P2MP or mLDP P2MP tunnels. Table 1 lists the differences between RSVP-TE P2MP tunnels and mLDP P2MP tunnels.

Table 1 Differences between RSVP-TE P2MP tunnels and mLDP P2MP tunnels

Tunnel Type

Tunnel Establishment Method

Characteristic

RSVP-TE P2MP tunnel

Established from the root node.

RSVP-TE P2MP tunnels support bandwidth reservation and can ensure service quality during network congestion. Use RSVP-TE P2MP tunnels to carry PMSI tunnels if high service quality is required.

mLDP P2MP tunnel

Established from a leaf node.

mLDP P2MP tunnels do not support bandwidth reservation and cannot ensure service quality during network congestion. Configuring an mLDP P2MP tunnel, however, is easier than configuring an RSVP-TE P2MP tunnel. Use mLDP P2MP tunnels to carry PMSI tunnels if high service quality is not required.

Theoretically, a P-tunnel can carry the traffic of one or multiple MVPNs. However, in NetEngine 8000 F, a P-tunnel can carry the traffic of only one MVPN.

On an MVPN that uses BGP as the signaling protocol, a sender PE distributes information about the P-tunnel in a new BGP attribute called PMSI. PMSI tunnels are the logical tunnels used by the public network to transmit VPN multicast data, and P-tunnels are the actual tunnels used by the public network to transmit VPN multicast data. A sender PE uses PMSI tunnels to send specific VPN multicast data to receiver PEs. A receiver PE uses PMSI tunnel information to determine which multicast data is sent by the multicast source on the same MVPN as itself. There are two types of PMSI tunnels: I-PMSI tunnels and S-PMSI tunnels.Table 2 lists the differences between I-PMSI and S-PMSI tunnels.
Table 2 I-PMSI and S-PMSI

PMSI Tunnel Type

Description

Characteristic

I-PMSI tunnel

An I-PMSI tunnel connects to all PEs on an MVPN.

Multicast data sent over an I-PMSI tunnel can be received by all PEs on the MVPN. In a VPN instance, one PE corresponds to only one I-PMSI tunnel.

S-PMSI tunnel

An S-PMSI tunnel connects to the sender and receiver PEs of specific sources and multicast groups.

Multicast data sent over an S-PMSI tunnel is received by only PEs interested in the data. In a VPN instance, one PE can correspond to multiple S-PMSI tunnels.
A public network tunnel can consist of one PMSI logical tunnel or multiple interconnected PMSI tunnels. The former is a non-segmented tunnel, and the latter forms a segmented tunnel.
  • For a non-segment tunnel, the public network between the sender PE and receiver PE uses the same MPLS protocol. Therefore, an MPLS P2MP tunnel can be used to set up a PSMI logical tunnel to carry multicast traffic.
  • For a segmented tunnel, different areas on the public network between the sender PE and receiver PE use different MPLS protocols. Therefore, PMSI tunnels need to be established in each area based on the MPLS protocol type and MPLS P2MP tunnel type. In addition, tunnel stitching must be configured on area connection nodes to stitch PMSI tunnels in different areas into one tunnel to carry the data traffic of the MVPN. Currently, the NetEngine 8000 F supports intra-AS segmented tunnels, not inter-AS segmented tunnels.

MVPN Targets

MVPN targets are used to control MVPN A-D route advertisement. MVPN targets function in a similar way as VPN targets used on unicast VPNs and are also classified into two types:
  • Export MVPN target: A PE adds the export MVPN target to an MVPN instance before advertising this route.
  • Import MVPN target: After receiving an MVPN A-D route from another PE, a PE matches the export MVPN target of the route against the import MVPN targets of its VPN instances. If the export MVPN target matches the import MVPN target of a VPN instance, the PE accepts the MVPN A-D route and records the sender PE as an MVPN member. If the export MVPN target does not match the import MVPN target of any VPN instance, the PE drops the MVPN A-D route.

By default, if you do not configure MVPN targets for an MVPN, MVPN A-D routes carry the VPN target communities that are attached to unicast VPN-IPv4 routes. If the unicast and multicast network topologies are congruent, you do not need to configure MVPN targets for MVPN A-D routes. If they are not congruent, configure MVPN targets for MVPN A-D routes.

Parent Topic: Understanding NG MVPN
Copyright © Huawei Technologies Co., Ltd.
Copyright © Huawei Technologies Co., Ltd.
< Previous topic Next topic >