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Example: Configuring Nonstop Active Routing for PIM

Understanding Nonstop Active Routing for PIM

Nonstop active routing configurations include two Routing Engines that share information so that routing is not interrupted during Routing Engine failover. When nonstop active routing is configured on a dual Routing Engine platform, the PIM control state is replicated on both Routing Engines.

This PIM state information includes:

  • Neighbor relationships

  • Join and prune information

  • RP-set information

  • Synchronization between routes and next hops and the forwarding state between the two Routing Engines

The PIM control state is maintained on the backup Routing Engine by the replication of state information from the primary to the backup Routing Engine and having the backup Routing Engine react to route installation and modification in the [instance].inet.1 routing table on the primary Routing Engine. The backup Routing Engine does not send or receive PIM protocol packets directly. In addition, the backup Routing Engine uses the dynamic interfaces created by the primary Routing Engine. These dynamic interfaces include PIM encapsulation, de-encapsulation, and multicast tunnel interfaces.


The clear pim join, clear pim register, and clear pim statistics operational mode commands are not supported on the backup Routing Engine when nonstop active routing is enabled.

To enable nonstop active routing for PIM (in addition to the PIM configuration on the primary Routing Engine), you must include the following statements at the [edit] hierarchy level:

  • chassis redundancy graceful-switchover

  • routing-options nonstop-routing

  • system commit synchronize

Example: Configuring Nonstop Active Routing with PIM

This example shows how to configure nonstop active routing for PIM-based multicast IPv4 and IPv6 traffic.


For nonstop active routing for PIM-based multicast traffic to work with IPv6, the routing device must be running Junos OS Release 10.4 or above.

Before you begin:

  • Configure the router interfaces. See the Network Interfaces Configuration Guide.

  • Configure an interior gateway protocol or static routing. See the Routing Protocols Configuration Guide.

  • Configure a multicast group membership protocol (IGMP or MLD). See Understanding IGMP and Understanding MLD.


Junos OS supports nonstop active routing in the following PIM scenarios:

  • Dense mode

  • Sparse mode

  • SSM

  • Static RP

  • Auto-RP (for IPv4 only)

  • Bootstrap router

  • Embedded RP on the non-RP router (for IPv6 only)

  • BFD support

  • Draft Rosen Multicast VPNs and BGP Multicast VPNs (use the advertise-from-main-vpn-tables option at the [edit protocols bgp] hierarchy level, to synchronize MVPN routes, cmcast, provider-tunnel and forwarding information between the primary and the backup Routing Engines).

  • Policy features such as neighbor policy, bootstrap router export and import policies, scope policy, flow maps, and reverse path forwarding (RPF) check policies

In Junos OS release 13.3, multicast VPNs are not supported with nonstop active routing. Policy-based features (such as neighbor policy, join policy, BSR policy, scope policy, flow maps, and RPF check policy) are not supported with nonstop active routing.

This example uses static RP. The interfaces are configured to receive both IPv4 and IPv6 traffic. R2 provides RP services as the local RP. Note that nonstop active routing is not supported on the RP router. The configuration shown in this example is on R1.


Figure 1 shows the topology used in this example.

Figure 1: Nonstop Active Routing in PIM DomainNonstop Active Routing in PIM Domain


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, copy and paste the commands into the CLI at the [edit] hierarchy level, and then enter commit from configuration mode.



Step-by-Step Procedure

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

To configure nonstop active routing on R1:

  1. Synchronize the Routing Engines.

  2. Enable graceful Routing Engine switchover.

  3. Configure R1’s interfaces.

  4. Configure OSPF for IPv4 on R1.

  5. Configure OSPF for IPv6 on R1.

  6. Configure PIM on R1. The PIM static address points to the RP router (R2).

  7. Configure per-packet load balancing on R1.

  8. Apply the load-balance policy on R1.

  9. Configure nonstop routing on R1.

Step-by-Step Procedure

For troubleshooting, configure system log and tracing operations.

  1. Enable system log messages.

  2. Trace interface operations.

  3. Trace IGP operations for IPv4.

  4. Trace IGP operations for IPv6.

  5. Trace PIM operations.

  6. Trace all routing protocol functionality.

  7. Trace forwarding table operations.

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


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


To verify the configuration, run the following commands:

  • show pim join extensive

  • show pim neighbors inet detail

  • show pim neighbors inet6 detail

  • show pim rps inet detail

  • show pim rps inet6 detail

  • show multicast route inet extensive

  • show multicast route inet6 extensive

  • show route table inet.1 detail

  • show route table inet6.1 detail

Configuring PIM Sparse Mode Graceful Restart

You can configure PIM sparse mode to continue to forward existing multicast packet streams during a routing process failure and restart. Only PIM sparse mode can be configured this way. The routing platform does not forward multicast packets for protocols other than PIM during graceful restart, because all other multicast protocols must restart after a routing process failure. If you configure PIM sparse-dense mode, only sparse multicast groups benefit from a graceful restart.

The routing platform does not forward new streams until after the restart is complete. After restart, the routing platform refreshes the forwarding state with any updates that were received from neighbors during the restart period. For example, the routing platform relearns the join and prune states of neighbors during the restart, but it does not apply the changes to the forwarding table until after the restart.

When PIM sparse mode is enabled, the routing platform generates a unique 32-bit random number called a generation identifier. Generation identifiers are included by default in PIM hello messages, as specified in the Internet draft draft-ietf-pim-sm-v2-new-10.txt. When a routing platform receives PIM hello messages containing generation identifiers on a point-to-point interface, the Junos OS activates an algorithm that optimizes graceful restart.

Before PIM sparse mode graceful restart occurs, each routing platform creates a generation identifier and sends it to its multicast neighbors. If a routing platform with PIM sparse mode restarts, it creates a new generation identifier and sends it to neighbors. When a neighbor receives the new identifier, it resends multicast updates to the restarting router to allow it to exit graceful restart efficiently. The restart phase is complete when the restart duration timer expires.

Multicast forwarding can be interrupted in two ways. First, if the underlying routing protocol is unstable, multicast RPF checks can fail and cause an interruption. Second, because the forwarding table is not updated during the graceful restart period, new multicast streams are not forwarded until graceful restart is complete.

You can configure graceful restart globally or for a routing instance. This example shows how to configure graceful restart globally.

To configure graceful restart for PIM sparse mode:

  1. Enable graceful restart.
  2. (Optional) Configure the amount of time the routing device waits (in seconds) to complete PIM sparse mode graceful restart. By default, the router allows 60 seconds. The range is from 30 through 300 seconds. After this restart time, the Routing Engine resumes normal multicast operation.
  3. Monitor the operation of PIM graceful restart by running the show pim neighbors command. In the command output, look for the G flag in the Option field. The G flag stands for generation identifier. Also run the show task replication command to verify the status of GRES and NSR.
Release History Table
In Junos OS release 13.3, multicast VPNs are not supported with nonstop active routing. Policy-based features (such as neighbor policy, join policy, BSR policy, scope policy, flow maps, and RPF check policy) are not supported with nonstop active routing.
For nonstop active routing for PIM-based multicast traffic to work with IPv6, the routing device must be running Junos OS Release 10.4 or above.