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Example: Configuring Multicast-Only Fast Reroute in a Multipoint LDP Domain

 

This example shows how to configure multicast-only fast reroute (MoFRR) to minimize packet loss in a network when there is a link failure.

Multipoint LDP MoFRR is used at the egress node of an MPLS network, where the packets are forwarded to an IP network. In the case of multipoint LDP MoFRR, the two paths toward the upstream provider edge (PE) router are established for receiving two streams of MPLS packets at the label-edge router (LER). One of the streams (the primary) is accepted, and the other one (the backup) is dropped at the LER. The backup stream is accepted if the primary path fails.

Requirements

No special configuration beyond device initialization is required before configuring this example.

In a multipoint LDP domain, for MoFRR to work, only the egress PE router needs to have MoFRR enabled. The other routers do not need to support MoFRR.

MoFRR is supported on MX Series platforms with MPC line cards. As a prerequisite, the router must be set to network-services enhanced-ip mode, and all the line-cards in the platform must be MPCs.

This example requires Junos OS Release 14.1 or later on the egress PE router.

Overview

In this example, Device R3 is the egress edge router. MoFRR is enabled on this device only.

OSPF is used for connectivity, though any interior gateway protocol (IGP) or static routes can be used.

For testing purposes, routers are used to simulate the source and the receiver. Device R4 and Device R8 are configured to statically join the desired group by using the set protocols igmp interface interface-name static group group command. In the case when a real multicast receiver host is not available, as in this example, this static IGMP configuration is useful. On the receivers, to make them listen to the multicast group address, this example uses set protocols sap listen group.

MoFRR configuration includes a policy option that is not shown in this example, but is explained separately. The option is configured as follows:

Topology

Figure 1 shows the sample network.

Figure 1: MoFRR in a Multipoint LDP Domain
MoFRR in a Multipoint LDP Domain

CLI Quick Configuration shows the configuration for all of the devices in Figure 1.

The section Configuration describes the steps on Device R3.

CLI Quick Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Device src1

Device src2

Device R1

Device R2

Device R3

Device R4

Device R5

Device R6

Device R7

Device R8

Configuration

Step-by-Step Procedure

The following example requires that you navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

To configure Device R3:

  1. Enable enhanced IP mode.
  2. Configure the device interfaces.
  3. Configure the autonomous system (AS) number.
  4. Configure the routing policies.
  5. Configure PIM.
  6. Configure LDP.
  7. Configure an IGP or static routes.
  8. Configure internal BGP.
  9. Configure MPLS and, optionally, RSVP.
  10. Enable MoFRR.

Results

From configuration mode, confirm your configuration by entering the show chassis, show interfaces, show protocols, show policy-options, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

If you are done configuring the device, enter commit from configuration mode.

Verification

Confirm that the configuration is working properly.

Checking the LDP Point-to-Multipoint Forwarding Equivalency Classes

Purpose

Make sure the MoFRR is enabled, and determine what labels are being used.

Action

user@R3> show ldp p2mp fec

Meaning

The output shows that MoFRR is enabled, and it shows that the labels 301568 and 301600 are being used for the two multipoint LDP point-to-multipoint LSPs.

Examining the Label Information

Purpose

Make sure that the egress device has two upstream interfaces for the multicast group join.

Action

user@R3> show route label 301568 detail


user@R3> show route label 301600 detail

Meaning

The output shows the primary upstream paths and the backup upstream paths. It also shows the RPF next hops.

Checking the Multicast Routes

Purpose

Examine the IP multicast forwarding table to make sure that there is an upstream RPF interface list, with a primary and a backup interface.

Action

user@R3> show ldp p2mp path

Meaning

The output shows primary and backup sessions, and RPF next hops.

Checking the LDP Point-to-Multipoint Traffic Statistics

Purpose

Make sure that both primary and backup statistics are listed.

Action

Meaning

The output shows both primary and backup routes with the labels.