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

This example shows how to configure data multicast distribution trees (MDTs) in a Draft Rosen Layer 3 VPN operating in any-source multicast mode. This example is based on the Junos implementation of RFC 4364, BGP/MPLS IP Virtual Private Networks (VPNs) and based on Section Two of the IETF Internet draft draft-rosen-vpn-mcast-06.txt, Multicast in MPLS/BGP VPNs (expires April 2004).

• Requirements
• Overview
• Configuration
• Verification

Requirements

Before you begin:

• Configure the Draft Rosen multicast over Layer 3 VPN scenario. See Example: Basic IPv4 Multicast over a Layer 3 VPN Configuration or Example: IPv4 Multicast with Interprovider VPNs Configuration in the Multicast over Layer 3 VPNs Feature Guide.
• Make sure 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.

Overview

By using data multicast distribution trees (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 ignore the new tunnel. Conversely, neighbors that do have receivers for the multicast traffic 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.

By default, automatic creation of data MDTs is disabled.

Because data MDTs apply to VPNs and VRF routing instances, you cannot configure MDT statements in the master routing instance.

This example includes the following configuration options:

• group—Specifies the multicast group address to which the threshold applies. This could be a well-known address for a certain type of multicast traffic.

  The group address can be explicit (all 32 bits of the address specified) or a prefix (network address and prefix length specified). Explicit and prefix address forms can be combined if they do not overlap. Overlapping configurations, in which prefix and more explicit address forms are used for the same source or group address, are not supported.

• group-range—Specifies the multicast group IP address range used when a new data MDT needs to be initiated on the PE router. For each new data MDT, one address is automatically selected from the configured group range.

  The PE router implementing data MDTs for a local multicast source must be configured with a range of multicast group addresses. Group addresses that fall within the configured range are used in the join messages for the data MDTs created in this VRF instance. Any multicast address range can be used as the multicast prefix; however, the group address range cannot overlap the default MDT group address configured for any VPN on the router. If you configure overlapping group addresses, the configuration commit operation fails.

• pim—Supports data MDTs for service provider tunnels operating in any-source multicast mode.
• rate—Specifies the data rate that initiates the creation of data MDTs. When the source traffic in the VRF exceeds the configured data rate, a new tunnel is created. The range is from 10 kilobits per second (Kbps), the default, to 1 gigabit per second (Gbps, equivalent to 1,000,000 Kbps).
• source—Specifies the unicast address of the source of the multicast traffic. It can be a source locally attached to or reached through the PE router. A group can have more than one source.

  The source addresses can be explicit (all 32 bits of the address specified) or a prefix (network address and prefix length specified). Explicit and prefix address forms can be combined if they do not overlap. Overlapping configurations, in which prefix and more explicit address forms are used for the same source or group address, are not supported.

• threshold—Associates a rate with a group and a source. The PE router implementing data MDTs for a local multicast source must establish a data MDT-creation threshold for a multicast group and source.

  When the traffic stops or the rate falls below the threshold value, the source PE router switches back to the default MDT.

• tunnel-limit—Specifies the maximum number of data MDTs that can be created for a single routing instance. The PE router implementing a data MDT for a local multicast source must establish a limit for the number of data MDTs created in this VRF instance. If the limit is 0 (the default), then no data MDTs are created for this VRF instance.

  If the number of data MDT tunnels exceeds the maximum configured tunnel limit for the VRF, then no new tunnels are created. Traffic that exceeds the configured threshold is sent on the default MDT.

  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.

Figure 51 shows a default MDT.

Figure 52 shows a data MDT.

Configuration

CLI Quick Configuration

To quickly configure data MDTs and provider tunnels, copy the following commands into a text file, remove any line breaks, and then paste the commands into the CLI.

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Modification of the Junos OS Configuration in Junos OS CLI, Release 10.3.

To configure data MDTs:

1. Configure the group range.

   [edit]user@host# edit routing-instances vpn-A pimmdt[edit routing-instances vpn-A pim mdt]user@host# set group-range 227.0.0.0/8

2. Configure a data MDT-creation threshold for a multicast group and source.

   [edit routing-instances vpn-A pim mdt]user@host# set threshold group 224.4.4.4 source 10.10.20.43 rate 10
3. Configure a tunnel limit.
   [edit routing-instances vpn-A pim mdt]user@host# set tunnel-limit 10

4. If you are done configuring the device, commit the configuration.

   [edit routing-instances vpn-A pim mdt]user@host# commit

Verification

You can monitor the operation of data MDTs by running the show pim mdt command. This command displays either the outgoing tunnels (the tunnels initiated by the local PE router), the incoming tunnels (tunnels initiated by the remote PE routers), or both.

You can trace the operation of data MDTs by including the mdt detail flag in the [edit protocols pim traceoptions] configuration. When this flag is set, all the mt interface-related activity is logged in trace files.

Related Topics

• Configuring PIM Trace Options
• Introduction to Configuring Layer 3 VPNs in the Junos VPNs Configuration Guide