Technical Documentation

Configuring Routing Protocols Graceful Restart

This topic includes the following sections:

Configuring Graceful Restart Globally

To configure graceful restart globally, include the graceful-restart statement at the [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.

[edit]routing-options {graceful-restart {disable;restart-duration seconds;}}

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 session has been established, the BGP session restarts and the peers negotiate graceful restart capabilities.

Configuring Graceful Restart Options for BGP

To configure the duration of the BGP graceful restart period, include the restart-time statement at the [edit protocols bgp graceful-restart] hierarchy level. To set the length of time the router waits to receive messages from restarting neighbors before declaring them down, include the stale-routes-time statement at the [edit protocols bgp graceful-restart] hierarchy level.

[edit]protocols {bgp {graceful-restart {disable;restart-time seconds;stale-routes-time seconds;}}}

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.

Configuring Graceful Restart Options for ES-IS

On J Series Services Routers, to configure the duration of the ES-IS graceful restart period, include the restart-duration statement at the [edit protocols esis graceful-restart] hierarchy level.

[edit]protocols {esis {graceful-restart {disable;restart-duration seconds;}}}

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 configure the duration of the IS-IS graceful restart period, include the restart-duration statement at the [edit protocols isis graceful-restart] hierarchy level.

[edit]protocols {isis {graceful-restart {disable;helper-disable;restart-duration seconds;}}}

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: 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 configure the duration of the OSPF/OSPFv3 graceful restart period, include the restart-duration statement at the [edit protocols (ospf | ospf3) graceful-restart] hierarchy level. To specify the length of time for which the router notifies helper routers that it has completed graceful restart, include the notify-duration at the [edit protocols (ospf | ospf3) graceful-restart] hierarchy level. Strict OSPF link-state advertisement (LSA) checking results in the termination of graceful restart by a helping router. To disable strict LSA checking, include the no-strict-lsa-checking statement at the [edit protocols (ospf | ospf3) graceful-restart] hierarchy level.

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

Note: 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 Release 7.5 and earlier and a routing platform running JUNOS Release 7.6 or later. As a workaround, make sure both routing platforms use the same JUNOS Software 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 configure the duration of the RIP or RIPng graceful restart period, include the restart-time statement at the [edit protocols (rip | ripng) graceful-restart] hierarchy level.

[edit]protocols {(rip | ripng) {graceful-restart {disable;restart-time seconds;}}}

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 Software 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 configure the duration of the PIM graceful restart period, include the restart-duration statement at the [edit protocols pim graceful-restart] hierarchy level:

[edit]protocols {pim {graceful-restart {disable;restart-duration seconds;}}}

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

To track the progress of a graceful restart event, you can configure graceful restart trace options flags for IS-IS and OSPF/OSPFv3. To configure graceful restart trace options, include the graceful-restart statement at the [edit protocols protocol traceoptions flag] hierarchy level:

[edit protocols]isis {traceoptions {flag graceful-restart;}}(ospf | ospf3) {traceoptions {flag graceful-restart;}}

Published: 2010-04-28