Example: Configuring Data MDTs and Provider Tunnels Operating in Source-Specific Multicast Mode

Before you begin:

• Make sure that the routing devices support multicast tunnel (mt) interfaces.

  A tunnel-capable PIC supports a maximum of 512 multicast tunnel interfaces. Both default and data MDTs contribute to this total. The default MDT uses two multicast tunnel interfaces (one for encapsulation and one for de-encapsulation). To enable an M Series or T Series router to support more than 512 multicast tunnel interfaces, another tunnel-capable PIC is required. See "Tunnel Services PICs and Multicast” and "Load Balancing Multicast Tunnel Interfaces Among Available PICs” in the Multicast Protocols User Guide.

• Make sure that the PE router has been configured for a draft-rosen Layer 3 multicast VPN operating in SSM mode in the provider core.

  In this type of multicast VPN, PE routers discover one another by sending MDT subsequent address family identifier (MDT-SAFI) BGP network layer reachability information (NLRI) advertisements. Key configuration statements for the master instance are highlighted in Table 1. Key configuration statements for the VRF instance to which your PE router is attached are highlighted in Table 2. For complete configuration details, see "Example: Configuring Source-Specific Multicast for Draft-Rosen Multicast VPNs" in the Multicast Protocols User Guide.

By using data MDTs in a Layer 3 VPN, you can prevent multicast packets from being flooded unnecessarily to specified provider edge (PE) routers within a VPN group. This option is primarily useful for PE routers in your Layer 3 VPN multicast network that have no receivers for the multicast traffic from a particular source.

• When a PE router that is directly connected to the multicast source (also called the source PE) receives Layer 3 VPN multicast traffic that exceeds a configured threshold, a new data MDT tunnel is established between the PE router connected to the source site and its remote PE router neighbors.

• The source PE advertises the new data MDT group as long as the source is active. The periodic announcement is sent over the default MDT for the VRF. Because the data MDT announcement is sent over the default tunnel, all the PE routers receive the announcement.

• Neighbors that do not have receivers for the multicast traffic cache the advertisement of the new data MDT group but ignore the new tunnel. Neighbors that do have receivers for the multicast traffic cache the advertisement of the new data MDT group and also send a PIM join message for the new group.

• The source PE encapsulates the VRF multicast traffic using the new data MDT group and stops the packet flow over the default multicast tree. If the multicast traffic level drops back below the threshold, the data MDT is torn down automatically and traffic flows back across the default multicast tree.

• If a PE router that has not yet joined the new data MDT group receives a PIM join message for a new receiver for which (S,G) traffic is already flowing over the data MDT in the provider core, then that PE router can obtain the new group address from its cache and can join the data-MDT immediately without waiting up to 59 seconds for the next data MDT advertisement.

By default, automatic creation of data MDTs is disabled.

The following sections summarize the data MDT configuration statements used in this example and in the prerequisite configuration for this example:

• In the master instance, the PE router’s prerequisite draft-rosen PIM-SSM multicast configuration includes statements that directly support the data MDT configuration you will enable in this example. Table 1 highlights some of these statements^†.

  Table 1: Data MDTS—Key Prerequisites in the Master Instance

  Statement	Description
  [edit protocols] pim { interface (Protocols PIM) interface-name <options>; }	Enables the PIM protocol on PE router interfaces.
  [edit protocols] bgp { group name { type internal; peer-as autonomous-system; neighbor address; family inet-mdt { signaling; } } } [edit routing-options] autonomous-system autonomous-system;	In the internal BGP full mesh between PE routers in the VRF instance, enables the BGP protocol to carry MDT-SAFI NLRI signaling messages for IPv4 traffic in Layer 3 VPNs.
  [edit routing-options] multicast { ssm-groups [ ip-addresses ]; }	(Optional) Configures one or more SSM groups to use inside the provider network in addition to the default SSM group address range of 232.0.0.0/8. Note: For this example, it is assumed that you previously specified an additional SSM group address range of 239.0.0.0/8.
  † This table contains only a partial list of the PE router configuration statements for a draft-rosen multicast VPN operating in SSM mode in the provider core. For complete configuration information about this prerequisite, see “Example: Configuring Source-Specific Multicast for Draft-Rosen Multicast VPNs” in the Multicast Protocols User Guide.

• In the VRF instance to which the PE router is attached—at the [edit routing-instances name] hierarchy level—the PE router’s prerequisite draft-rosen PIM-SSM multicast configuration includes statements that directly support the data MDT configuration you will enable in this example. Table 2 highlights some of these statements^‡.

  Table 2: Data MDTs—Key Prerequisites in the VRF Instance

  Statement	Description
  [edit routing-instances name] instance-type vrf; vrf-target community;	Creates a VRF table (instance-name.mdt.0) that contains the routes originating from and destined for the Layer 3 VPN. Creates a VRF export policy that automatically accepts routes from the instance-name.mdt.0 routing table. ensures proper PE autodiscovery using the inet-mdt address family You must also configure the interface and route-distinguisher statements for this type of routing instance.
  [edit routing-instances name] protocols { pim { mvpn { family { inet | inet6 { autodiscovery { inet-mdt; } } } } } }	Configures the PE router in a VPN to use an MDT-SAFI NLRI for autodiscovery of other PE routers:
  [edit routing-instances name] provider-tunnelfamily inet | inet6{ pim-ssm { group-address (Routing Instances) address; } }	Configures the PIM-SSM provider tunnel default MDT group address. Note: For this example, it assumed that you previously configured the PIM-SSM provider tunnel default MDT for the VPN instance ce1 with the group address 239.1.1.1. To verify the configuration of the default MDT tunnel for the VRF instance to which the PE router is attached, use the show pim mvpn operational mode command.
  ‡ This table contains only a partial list of the PE router configuration statements for a draft-rosen multicast VPN operating in SSM mode in the provider core. For complete configuration information about this prerequisite, see “Example: Configuring Source-Specific Multicast for Draft-Rosen Multicast VPNs” in the Multicast Protocols User Guide.

• For a rosen 7 MVPN—a draft-rosen multicast VPN with provider tunnels operating in SSM mode—you configure data MDT creation for a tunnel multicast group by including statements under the PIM-SSM provider tunnel configuration for the VRF instance associated with the multicast group. Because data MDTs are specific to VPNs and VRF routing instances, you cannot configure MDT statements in the primary routing instance. Table 3 summarizes the data MDT configuration statements for PIM-SSM provider tunnels.

  Table 3: Data MDTs for PIM-SSM Provider Tunnels in a Draft-Rosen MVPN

  Statement	Description
  [edit routing-instances name] provider-tunnel family inet | inet6{{ mdt { group-range multicast-prefix; } }	Configures the IP group range used when a new data MDT needs to be created in the VRF instance on the PE router. This address range cannot overlap the default MDT addresses of any other VPNs on the router. If you configure overlapping group ranges, the configuration commit fails. This statement has no default value. If you do not set the multicast-prefix to a valid, nonreserved multicast address range, then no data MDTs are created for this VRF instance. Note: For this example, it is assumed that you previously configured the PE router to automatically select an address from the 239.10.10.0/24 range when a new data MDT needs to be initiated.
  [edit routing-instances name] provider-tunnel family inet | inet6{{ mdt { tunnel-limit limit; } }	Configures the maximum number of data MDTs that can be created for the VRF instance. The default value is 0. If you do not configure the limit to a non-zero value, then no data MDTs are created for this VRF instance. The valid range is from 0 through 1024 for a VRF instance. There is a limit of 8000 tunnels for all data MDTs in all VRF instances on a PE router. If the configured maximum number of data MDT tunnels is reached, then no new tunnels are created for the VRF instance, and traffic that exceeds the configured threshold is sent on the default MDT. Note: For this example, you limit the number of data MDTs for the VRF instance to 10.
  [edit routing-instances name] provider-tunnel family inet | inet6{{ mdt { threshold { group group-address { source source-address { rate threshold-rate; } } } } }	Configures a data rate for the multicast source of a default MDT. When the source traffic in the VRF instance exceeds the configured data rate, a new tunnel is created. group group-address—Multicast group address of the default MDT that corresponds to a VRF instance to which the PE router is attached. The group-address explicit (all 32 bits of the address specified) or a prefix (network address and prefix length specified). This is typically a well-known address for a certain type of multicast traffic. source source-address—Unicast IP prefix of one or more multicast sources in the specified default MDT group. rate threshold-rate—Data rate for the multicast source to trigger the automatic creation of a data MDT. The data rate is specified in kilobits per second (Kbps). The default threshold-rate is 10 kilobits per second (Kbps). Note: For this example, you configure the following data MDT threshold: Multicast group address or address range to which the threshold limits apply—224.0.9.0/32 Multicast source address or address range to which the threshold limits apply—10.1.1.2/32 Data rate—10 Kbps When the traffic stops or the rate falls below the threshold value, the source PE router switches back to the default MDT.

Topology

Figure 1 shows a default MDT.

Figure 1: Default MDT

Figure 2 shows a data MDT.

Figure 2: Data MDT

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see the Junos OS CLI User Guide.

• CLI Quick Configuration
• Enabling Data MDTs and PIM-SSM Provider Tunnels on the Local PE Router Attached to a VRF
• (Optional) Enabling Logging of Detailed Trace Information for Multicast Tunnel Interfaces on the Local PE Router
• Results

To verify that the local PE router is managing data MDTs and PIM-SSM provider tunnels properly, perform the following tasks:

• Monitor Data MDTs Initiated for the Multicast Group
• Monitor Data MDT Group Addresses Cached by All PE Routers in the Multicast Group
• (Optional) View the Trace Log for Multicast Tunnel Interfaces