OSPF Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Release

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OSPF Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Release

OSPF route advertisement and timer control features

Updated: June 26, 2026

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Explains OSPF route advertisement and timer control features, covering how these mechanisms manage router information, update timing, and enable accurate and efficient routing tables.

OSPF route advertisement and timer control features are routing protocol mechanisms that:

  • manage the dissemination of network link-state information,

  • regulate the timing of network topology updates, and

  • determine how routers on Cisco 8000 Series platforms maintain accurate and efficient routing tables.

Link-State Advertisement Types for OSPF Version 2

Each Link-State Advertisement (LSA) type serves a specific purpose:

  • Router LSA (Type 1): Describes the links a router has within a single area and the cost of each link. Indicates path computation capabilities, router roles (ABR or ASBR), virtual links, and advertises stub networks. Flooded within an area only.

  • Network LSA (Type 2): Describes link-state and cost information for all routers attached to a multiaccess network segment. Generated by the designated router and lists all router interfaces attached.

  • Summary LSA for ABRs (Type 3): Advertises internal networks to routers in other areas (interarea routes). May represent single or aggregated networks. Only ABRs generate these LSAs.

  • Summary LSA for ASBRs (Type 4): Advertises an ASBR and the cost to reach it. Used to determine the best path to external networks. Generated by ABRs.

  • Autonomous System External LSA (Type 5): Redistributes routes from another autonomous system, typically from a different routing protocol.

  • Autonomous System External LSA (Type 7): Carries external route information within a Not-So-Stubby Area (NSSA). Originated and advertised within an NSSA only and not flooded to other areas.

  • Intra-area-prefix LSA (Type 9): Originated for routers or transit networks with unique link-state IDs that describe association and contain prefixes for stub and transit networks.

  • Area local scope (Type 10): Opaque LSAs not flooded past the borders of their associated area.

  • Link-state (Type 11): Flooded throughout the autonomous system, similar flooding scope to Type 5 LSAs but not implemented in stub areas.

Additional reference information

The OSPF FIB Download Notification feature minimizes ingress traffic drops after line card reload and is enabled by default.

OSPF registers with the Routing Information Base (RIB) using the Interface Table Attribute Library (ITAL), which keeps interfaces down until all routes are downloaded to the Forwarding Information Base (FIB). The "Interface Up" notification occurs when routes are complete.

RIB notifications include:

  • Node is lost

  • Node is created

  • Node’s FIB upload completion

OSPFv3 Timers and SPF Throttle Values

  • timers throttle lsa all: start-interval 50 ms, hold-interval 200 ms

  • timers throttle spf: spf-start 50 ms, spf-hold 200 ms, spf-max-wait 5000 ms

OSPF SPF Throttling

SPF scheduling allows millisecond intervals for calculations and helps delay SPF calculations during network instability. SPF is scheduled for topology changes, and multiple events may trigger a single run.

SPF calculation intervals are chosen dynamically based on topology stability. Intervals double until reaching max-wait, then remain constant. Intervals reset based on timing parameters if events occur after max-wait begins.

Example:

timers spf 5 1000 90000

Start interval: 5 ms; initial wait: 1000 ms; maximum wait: 90,000 ms. Wait intervals double until max-wait, then reset as topology stabilizes.

Subdefinitions for OSPFv3 LSA Types

  • Router LSA (Type 1): No address information; protocol independent; multiple router LSAs may need to be concatenated before SPF calculation.

  • Network LSA (Type 2): No address information; protocol independent; generated by designated router.

  • Interarea-prefix LSA (Type 3): Addresses are "prefix and prefix length" (default route = prefix length 0).

  • Interarea-router LSA (Type 4): Advertises ASBR and cost.

  • Autonomous System External LSA (Type 5): Addresses are "prefix and prefix length." Default route = prefix length 0.

  • Type 7 LSA: Carries external information within NSSA.

  • Link LSA (Type 8): Flooded only within their link; communicates link-local address, IPv6 prefixes, and option bits.

  • Intra-area-prefix LSA (Type 9): Multiple per router/network; unique IDs describe association.

Address prefixes appear in most new LSAs as three fields: Prefix Length, Prefix Options, and Address Prefix. Inter-area and intra-area LSAs carry IPv6 prefix information that replaces the IPv4 information contained in router/network LSAs. Certain LSAs have expanded options fields (24 bits for IPv6 support). In OSPFv3, the link-state ID identifies database items, but addresses are carried in the LSA body.