Warm Standby For Ospf Version 3; Multicast-Intact Support For Ospf; Load Balancing In Ospf Version 2 And Ospfv3 - Cisco ASR 9000 Series Routing Configuration Manual

Warm Standby for OSPF Version 3

Warm Standby for OSPF Version 3
This feature helps OSPFv3 to initialize itself prior to Fail over (FO) and be ready to function before the failure
occurs. It reduces the downtime during switchover. By default, the router sends hello packets every 40 seconds.
With warm standby process for each OSPF process running on the Active Route Processor, the corresponding
OSPF process must start on the Standby RP. There are no changes in configuration for this feature.
Warm-Standby is always enabled. This is an advantage for the systems running OSPFv3 as their IGP when
they do RP failover.

Multicast-Intact Support for OSPF

The multicast-intact feature provides the ability to run multicast routing (PIM) when IGP shortcuts are
configured and active on the router. Both OSPFv2 and IS-IS support the multicast-intact feature.
You can enable multicast-intact in the IGP when multicast routing protocols (PIM) are configured and IGP
shortcuts are configured on the router. IGP shortcuts are MPLS tunnels that are exposed to IGP. The IGP
routes IP traffic over these tunnels to destinations that are downstream from the egress router of the tunnel
(from an SPF perspective). PIM cannot use IGP shortcuts for propagating PIM joins, because reverse path
forwarding (RPF) cannot work across a unidirectional tunnel.
When you enable multicast-intact on an IGP, the IGP publishes a parallel or alternate set of equal-cost next
hops for use by PIM. These next hops are called mcast-intact next hops. The mcast-intact next hops have the
following attributes:
• They are guaranteed not to contain any IGP shortcuts.
• They are not used for unicast routing but are used only by PIM to look up an IPv4 next-hop to a PIM
• They are not published to the FIB.
• When multicast-intact is enabled on an IGP, all IPv4 destinations that were learned through link-state
In OSPF, the max-paths (number of equal-cost next hops) limit is applied separately to the native and
mcast-intact next hops. The number of equal cost mcast-intact next hops is the same as that configured for
the native next hops.

Load Balancing in OSPF Version 2 and OSPFv3

When a router learns multiple routes to a specific network by using multiple routing processes (or routing
protocols), it installs the route with the lowest administrative distance in the routing table. Sometimes the
router must select a route from among many learned by using the same routing process with the same
administrative distance. In this case, the router chooses the path with the lowest cost (or metric) to the
destination. Each routing process calculates its cost differently; the costs may need to be manipulated to
achieve load balancing.
OSPF performs load balancing automatically. If OSPF finds that it can reach a destination through more than
one interface and each path has the same cost, it installs each path in the routing table. The only restriction
on the number of paths to the same destination is controlled by the maximum-paths (OSPF) command.
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advertisements are published with a set equal-cost mcast-intact next hops to the RIB. This attribute
applies even when the native next hops have no IGP shortcuts.
Implementing OSPF