Routing Around The Restarting Router To Minimize Network Instability; Unexpected Suspension Of Pim During Unified Issu - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - SERVICE AVAILABILITY CONFIGURATION GUIDE 2010-10-08 Configuration Manual

Routing Around the Restarting Router to Minimize Network Instability

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Unexpected Suspension of PIM During Unified ISSU

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Copyright © 2010, Juniper Networks, Inc.
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.
When traffic engineering has been configured, the traffic engineering metrics are also
increased. New tunnels are not established through the upgrading router and any tunnels
undergoing re-optimization in other routers go around the upgrading router.
OSPF support for unified ISSU does not depend on this configuration. If you do not issue
the overload advertise-high-metric issu command, the unified in-service software
upgrade can still proceed to successful completion without disrupting OSPF functionality.
Application Support for Unified ISSU on page 115
overload advertise-high-metric issu
issu start
You can minimize PIM traffic loss during the unified in-service software upgrade by issuing
the ip pim dr-priority command to set a priority so that PIM neighbors do not forward
traffic through the upgrading router. By default, a PIM interface has a priority of one. If
you set the priority to one, the lowest possible priority, then the upgrading router is not
selected to be a designated router in the PIM network if an interface on another router
in that network has a higher priority.
Application Support for Unified ISSU on page 115
ip pim dr-priority
Chapter 5: Configuring a Unified In-Service Software Upgrade
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