NG MVPN Control Messages

The key mechanisms of NG MVPN are VPN multicast route transmission and public network tunnel establishment. The two mechanisms are implemented by transmitting BGP messages on the public network. These messages are NG MVPN control messages.

PEs on an NG MVPN exchange control messages to implement functions such as MVPN membership autodiscovery, PMSI tunnel establishment, and VPN multicast group joining and leaving. The following describes these NG MVPN control messages. All examples in this section are based on the network shown in Figure 1. On this network:

The service provider's backbone network provides both unicast and multicast VPN services for vpn1. The AS number of the backbone network is 65001.
The multicast source resides at Site1, accesses PE1 through CE1, and sends multicast traffic to multicast group 232.1.1.1.
Multicast receivers reside at Site2 and Site3.
The backbone network provides MVPN services for vpn1 over RSVP-TE or mLDP P2MP tunnels.

Figure 1 NG MVPN
Click to enlarge

MVPN NLRI

In NG MVPN, MVPN routing information is carried in the network layer reachability information (NLRI) field of BGP Update messages. The NLRI containing MVPN routing information is called MVPN NLRI. The SAFI of the MVPN NLRI is 5. Figure 2 shows the MVPN NLRI format.

Figure 2 MVPN NLRI format

**Table 1** Description of the fields in the MVPN NLRI
Field	Description
Route type	Type of an MVPN route. Seven types of MVPN routes are available. For more information, see Table 2.
Length	Length of the Route type specific field in the MVPN NLRI.
Route type specific	MVPN routing information. The value of this field depends on the Route type field. For details, see Table 2.

Table 2 describes the types and functions of MVPN routes. Type 1-5 routes are called MVPN A-D routes. These routes are used for MVPN membership autodiscovery and P2MP tunnel establishment. Type 6 and Type 7 routes are called C-multicast routes (C is short for Customer. C-multicast routes refer to multicast routes from the private network). These routes are used for VPN multicast group joining and VPN multicast traffic forwarding.

**Table 2** Types and functions of MVPN routes
Type	Function	Route Type Specific Field Format	Parameter Description
1: Intra-AS I-PMSI A-D route	Used for MVPN membership autodiscovery in intra-AS scenarios. MVPN-capable PEs use Intra-AS I-PMSI A-D routes to advertise and learn intra-AS MVPN membership information.	Figure 3	RD: route distinguisher, an 8-byte field in a VPNv4 address. An RD and a 4-byte IPv4 address prefix form a VPNv4 address, which is used to differentiate IPv4 prefixes using the same address space. Originating router's IP address: IP address of the device that originates Intra-AS A-D routes. In NetEngine 8000 F implementation, the value is the MVPN ID of the device that originates BGP A-D routes.
2: Inter-AS I-PMSI A-D route	Used for MVPN membership autodiscovery in inter-AS scenarios. MVPN-capable ASBRs use Inter-AS I-PMSI A-D routes to advertise and learn inter-AS MVPN membership information.	Figure 4	RD: route distinguisher, an 8-byte field in a VPNv4 address. An RD and a 4-byte IPv4 address prefix form a VPNv4 address, which is used to differentiate IPv4 prefixes using the same address space. Source AS: AS where the source device that sends Inter-AS A-D routes resides.
3: S-PMSI A-D route	Used by a sender PE to initiate a selective P-tunnel for a particular (C-S, C-G).	Figure 5	RD: route distinguisher, an 8-byte field in a VPNv4 address. An RD and a 4-byte IPv4 address prefix form a VPNv4 address, which is used to differentiate IPv4 prefixes using the same address space. Multicast source length: length of a multicast source address. The value is 32 if the multicast group address is an IPv4 address or 128 if the multicast group address is an IPv6 address. Multicast source: address of a multicast source. Multicast group length: length of a multicast group address. The value is 32 if the multicast group address is an IPv4 address or 128 if the multicast group address is an IPv6 address. Multicast group: address of a multicast group. Originating router's IP address: IP address of the device that originates A-D routes. In NetEngine 8000 F implementation, the value is the MVPN ID of the device that originates BGP A-D routes.
4: Leaf A-D route	Used to respond to a Type 1 Intra-AS I-PMSI A-D route with the flags field in the PMSI attribute being 1 or a Type 3 S-PMSI A-D route. If a receiver PE has a request for establishing an S-PMSI tunnel, it sends a Leaf A-D route to help the sender PE collect tunnel information.	Figure 6 NOTE: The Route key is set to the MVPN NLRI of the S-PMSI A-D route received.	Route key: set to the MVPN NLRI of the S-PMSI A-D route received. Originating router's IP address: IP address of the device that originates A-D routes. In NetEngine 8000 F implementation, the value is the MVPN ID of the device that originates BGP A-D routes.
5: Source Active A-D route	Used by PEs to learn the identity of active VPN multicast sources.	Figure 7	RD: RD of the sender PE connected to the multicast source. Multicast source length: length of a multicast source address. The value is 32 if the multicast group address is an IPv4 address or 128 if the multicast group address is an IPv6 address. Multicast source: address of a multicast source. Multicast group length: length of a multicast group address. The value is 32 if the multicast group address is an IPv4 address or 128 if the multicast group address is an IPv6 address. Multicast group: address of a multicast group.
6: Shared Tree Join route	Used in (, G) scenarios. A Shared Tree Join route is originated when a receiver PE receives a (C-, C-G) PIM Join message. A receiver PE sends the Shared Tree Join route to sender PEs with which it has established BGP peer relationships. NOTE: The (, G) PIM-SM join initiated by a VPN is called a (C-, C-G) PIM join.	Figure 8 NOTE: Shared Tree Join routes and Source Tree Join routes have the same NLRI format. The multicast source address is the RP address for (C-*, C-G) joins.	Route type: MVPN route type. The value 6 indicates that the route is a Type 6 route (Shared Tree Join route). Rt-import: VRF Route Import Extended Community of the unicast route to the multicast source. For more information about the VRF Route Import Extended Community, see MVPN Extended Communities. The VRF Route Import Extended Community is used by sender PEs to determine whether to process the BGP C-multicast route sent by a receiver PE. This attribute also helps a sender PE to determine to which VPN instance routing table a BGP C-multicast route should be added. Next hop: next hop address. RD: RD of the sender PE connected to the multicast source. Source AS: Source AS Extended Community of the unicast route to the multicast source. For more information about the Source AS Extended Community, see MVPN Extended Communities. Multicast source length: length of a multicast source address. The value is 32 if the multicast group address is an IPv4 address or 128 if the multicast group address is an IPv6 address. RP address: rendezvous point address. Multicast group length: length of a multicast group address. The value is 32 if the multicast group address is an IPv4 address or 128 if the multicast group address is an IPv6 address. Multicast group: address of a multicast group.
7: Source Tree Join route	Used in (S, G) scenarios. A Source Tree Join route is originated when a receiver PE receives a (C-S, C-G) PIM Join message. A receiver PE sends the Source Tree Join route to sender PEs with which it has established BGP peer relationships. NOTE: The (S, G) PIM-SSM join initiated by a VPN is called a (C-S, C-G) PIM join.	Figure 9	RD: RD of the sender PE connected to the multicast source. Source AS: Source AS Extended Community of the unicast route to the multicast source. For more information about the Source AS Extended Community, see MVPN Extended Communities. Multicast source length: length of a multicast source address. The value is 32 if the multicast group address is an IPv4 address or 128 if the multicast group address is an IPv6 address. Multicast source: address of a multicast source. Multicast group length: length of a multicast group address. The value is 32 if the multicast group address is an IPv4 address or 128 if the multicast group address is an IPv6 address. Multicast group: address of a multicast group.

Route Type Specific field format

Figure 3 Type 1: Intra-AS I-PMSI A-D route field format

Figure 4 Type 2: Inter-AS I-PMSI A-D route field format

Figure 5 Type 3: S-PMSI A-D route field format

Figure 6 Type 4: Leaf A-D route field format

Figure 7 Type 5: Source Active A-D route field format

Figure 8 Type 6: Shared Tree Join route field format

Figure 9 Type 7: Source Tree Join route field format

PMSI Tunnel attribute

The PMSI Tunnel attribute carries P-tunnel information used for P-tunnel establishment. The following figure shows the PMSI Tunnel attribute format.

**Table 3** Description of fields for the PMSI Tunnel attribute
Format	Field	Description
	Flags	Flags bits. Currently, only one flag indicating whether leaf information is required is specified: If a receiver PE receives a Type 1 route (Intra-AS I-PMSI A-D route) or a Type 3 route (S-PMSI A-D route) and the Flags field of the PMSI Tunnel attribute in the route indicates that leaf information is not required, the receiver PE does not need to respond. If a receiver PE receives a Type 1 route (Intra-AS I-PMSI A-D route) or a Type 3 route (S-PMSI A-D route) and the Flags field of the PMSI Tunnel attribute in the route indicates that leaf information is required, the receiver PE needs to reply with the Type 4 route (Leaf A-D route).
	Tunnel type	Tunnel type, which can be: 0: No tunnel information present 1: RSVP-TE P2MP LSP 2: mLDP P2MP LSP 3: PIM-SSM Tree 4: PIM-SM Tree 5: BIDIR-PIM Tree 6: Ingress Replication 7: mLDP MP2MP LSP
	MPLS label	MPLS labels are used for VPN tunnel multiplexing. Currently, tunnel multiplexing is not supported.
	Tunnel identifier	Tunnel identifier. Its value depends on the value set in the Tunnel type field: If the tunnel type is RSVP-TE P2MP LSP, its value is <P2MP ID, Tunnel ID, Extended Tunnel ID>. If the tunnel type is mLDP P2MP LSP, its value is <Root node address, Opaque value>.

On an NG MVPN, the sender PE sets up the P-tunnel, and therefore is responsible for originating the PMSI Tunnel attribute. The PMSI Tunnel attribute can be attached to intra-AS I-PMSI A-D route, inter-AS I-PMSI A-D routes, or S-PMSI A-D routes and sent to receiver PEs. Figure 10 is an example that shows the format of an Intra-AS I-PMSI A-D route carrying the PMSI Tunnel attribute.

Figure 10 Intra-AS I-PMSI A-D route carrying the PMSI Tunnel attribute