Configuring Graceful Restart When Bgp And Ldp Are Configured; Configuring A Longer Dead Interval Than Normal; Routing Around The Restarting Router To Minimize Network Instability; Interruption In Traffic Forwarding For Layer 3 Routing Protocols During Unified - Juniper SERVICE AVAILABILITY - CONFIGURATION GUIDE V 11.1.X Configuration Manual

now unreachable. When the unified in-service software upgrade completes and the
routing protocols restart, the IS-IS neighbors can relearn the routes through the router.
You must also ensure that the OSPF neighbors have been configured as graceful
restart helper routers. During the unified ISSU initialization phase, OSPF graceful
restart on the upgrading router cannot verify whether its neighbors are helper routers,
and reports that fact by means of the CLI.

Configuring Graceful Restart When BGP and LDP Are Configured

When BGP, LDP, and OSPF are all configured on a router on which you want to
perform a unified in-service software upgrade, ensure that the OSPF graceful restart
timeout is longer than the LDP graceful restart timeout. The OSPF graceful restart
does not complete when the LDP graceful restart timeout is longer than the OSPF
graceful restart timeout. Configure OSPF graceful restart timeout with the
graceful-restart restart-time command. Configure LDP graceful restart timeout
with the mpls ldp graceful-restart timers max-recovery command.

Configuring a Longer Dead Interval Than Normal

To prevent OSPF from timing out to the OSPF neighbors, you must configure a dead
interval that is longer than the expected forwarding outage for the platform. During
the initialization phase, unified ISSU displays the recommended dead interval in a
warning message. For information about the expected forwarding outage, see

"Interruption in Traffic Forwarding for Layer 3 Routing Protocols During Unified

ISSU" on page 92

Routing Around the Restarting Router to Minimize Network Instability

NOTE: The situation described in this section is very uncommon. This rare
circumstance arises when you have redundant uplinks to the core and network
topology changes cause routes to go through the upgrading router. In a typical network
design, this is not an issue and you do not need to route peers around the upgrading
router.
During the unified ISSU upgrade phase, network instability can result if the restarting
router goes into an unstable state after the unified ISSU process fails. Some OSPF
traffic loss occurs during the resulting line module resets. For those reasons, you
might want OSPF peers to route around the router that is being upgraded.
You can use the overload advertise-high-metric issu command to cause the router
to advertise a high link cost to its neighbors so that they route around the upgrading
router. When you issue the issu start command, the router raises the link cost to the
maximum link cost on all interfaces running OSPF. The higher cost is advertised in
the OSPF LSAs. OSPF neighbors then choose a path with lower metrics to reach any
destination that was previously reached through the upgrading router. When unified
ISSU is completed, OSPF reverts the link costs back to the values that were configured
before the unified in-service software upgrade.
Chapter 4: Configuring a Unified In-Service Software Upgrade

OSPF Effects on Graceful Restart and Network Stability During Unified ISSU

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