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Configuring Routing Protocols Graceful Restart

Enabling Graceful Restart

By default, graceful restart is disabled. To enable graceful restart, include the graceful-restart statement at the [edit routing-instance instance-name routing-options] or [edit routing-options] hierarchy level.

To configure the duration of the graceful restart period, include the restart-duration at the [edit routing-options graceful-restart] hierarchy level.

Note: Helper mode (the ability to assist a neighboring router attempting a graceful restart) is enabled by default when you start the routing platform, even if graceful restart is not enabled. You can disable helper mode on a per-protocol basis.

To disable graceful restart globally, include the disable statement at the [edit routing-options graceful-restart] hierarchy level.

When graceful restart is enabled for all routing protocols at the [edit routing-options graceful-restart] hierarchy level, you can disable graceful restart on a per-protocol basis.

Note: If you configure graceful restart after a BGP or LDP session has been established, the BGP or LDP session restarts and the peers negotiate graceful restart capabilities. Also, the BGP peer routing statistics are reset to zero.

Configuring Graceful Restart Options for BGP

To disable BGP graceful restart capability for all BGP sessions, include the disable statement at the [edit protocols bgp graceful-restart] hierarchy level.

Note: To set BGP graceful restart properties or disable them for a group, include the desired statements at the [edit protocols bgp group group-name graceful-restart] hierarchy level. To set BGP graceful restart properties or disable them for a specific neighbor in a group, include the desired statements at the [edit protocols bgp group group-name neighbor ip-address graceful-restart] hierarchy level.

Note: Configuring graceful restart for BGP resets the BGP peer routing statistics to zero. Also, existing BGP sessions restart, and the peers negotiate graceful restart capabilities.

Configuring Graceful Restart Options for ES-IS

To disable ES-IS graceful restart capability, include the disable statement at the [edit protocols esis graceful-restart] hierarchy level.

Configuring Graceful Restart Options for IS-IS

To disable IS-IS graceful restart helper capability, include the helper-disable statement at the [edit protocols isis graceful-restart] hierarchy level. To disable IS-IS graceful restart capability, include the disable statement at the [edit protocols isis graceful-restart] hierarchy level.

Note: If you configure Bidirectional Forwarding Detection (BFD) and graceful restart for IS-IS, graceful restart might not work as expected.

Note: If adjacencies between the Routing Engine and the neighboring peer 'helper' routers time out, graceful restart protocol extensions are unable to notify the peer 'helper' routers about the impending restart. Graceful restart can then stop and cause interruptions in traffic. To ensure that these adjacencies are kept, change the hold-time for IS-IS protocols from the default of 27 seconds to a value higher than 40 seconds. See Example: Configuring IS-IS for GRES with Graceful Restart for more information.

Note: You can also track graceful restart events with the traceoptions statement at the [edit protocols isis] hierarchy level. For more information, see Tracking Graceful Restart Events.

Configuring Graceful Restart Options for OSPF and OSPFv3

To disable OSPF/OSPFv3 graceful restart, include the disable statement at the [edit protocols (ospf | ospf3) graceful-restart] hierarchy level.

Starting with Release 11.3, the Junos OS supports both the standard (based on RFC 3623, Graceful OSPF Restart) and the restart signaling-based (as specified in RFC 4811, RFC 4812, and RFC 4813) helper modes for OSPF version 2 graceful restart configurations. Both the standard and restart signaling-based helper modes are enabled by default. To disable the helper mode for OSPF version 2 graceful restart configurations, include the helper-disable <both | restart-signaling | standard> statement at the [edit protocols ospf graceful-restart] hierarchy level. Note that the last committed statement always takes precedence over the previous one.

To reenable the helper mode, delete the helper-disable statement from the configuration by using the delete protocols ospf graceful-restarthelper-disable <restart-signaling | standard | both> command. In this case also, the last executed command takes precedence over the previous ones.

Note: Restart signaling-based helper mode is not supported for OSPFv3 configurations. To disable helper mode for OSPFv3 configurations, include the helper-disable statement at the [edit protocols ospfv3 graceful-restart] hierarchy level.

Tip: You can also track graceful restart events with the traceoptions statement at the [edit protocols (ospf | ospf3)] hierarchy level. For more information, see Tracking Graceful Restart Events.

Note: You cannot enable OSPFv3 graceful restart between a routing platform running Junos OS Release 7.5 and earlier and a routing platform running Junos OS Release 7.6 or later. As a workaround, make sure both routing platforms use the same Junos OS version.

Note: If you configure BFD and graceful restart for OSPF, graceful restart might not work as expected.

Configuring Graceful Restart Options for RIP and RIPng

To disable RIP or RIPng graceful restart capability, include the disable statement at the [edit protocols (rip | ripng) graceful-restart] hierarchy level.

Configuring Graceful Restart Options for PIM Sparse Mode

PIM sparse mode continues to forward existing multicast packet streams during a graceful restart, but does not forward new streams until after the restart is complete. After a restart, the routing platform updates the forwarding state with any updates that were received from neighbors and occurred during the restart period. For example, the routing platform relearns the join and prune states of neighbors during the restart, but does not apply the changes to the forwarding table until after the restart.

PIM sparse mode-enabled routing platforms generate a unique 32-bit random number called a generation identifier. Generation identifiers are included by default in PIM hello messages, as specified in the IETF Internet draft Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised). When a routing platform receives PIM hellos containing generation identifiers on a point-to-point interface, 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 PIM sparse mode-enabled routing platform restarts, it creates a new generation identifier and sends it to its 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 completes when either the PIM state becomes stable or when the restart interval timer expires.

If a routing platform does not support generation identifiers or if PIM is enabled on multipoint interfaces, the PIM sparse mode graceful restart algorithm does not activate, and a default restart timer is used as the restart mechanism.

To disable PIM sparse mode graceful restart capability, include the disable statement at the [edit protocols pim graceful-restart] hierarchy level.

Note: Multicast forwarding can be interrupted in two ways. First, if the underlying routing protocol is unstable, multicast reverse-path-forwarding (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.

Tracking Graceful Restart Events