Describes OSPF scaling, optimization, and protection features for Cisco 8000 Series Routers running IOS XR, including OSPF behavior, dependencies, and key design considerations.
OSPF scale, optimization, and protection features are advanced routing mechanisms that
improve the scalability and convergence of OSPF on Cisco 8000 Series Routers,
optimize route installation and prefix handling for efficient operations, and
protect the network from resource exhaustion caused by excessive routing or link-state advertisements.
OSPF SPF Prefix Prioritization enables administrators to prioritize the installation of important prefixes, ensuring faster convergence for critical traffic (such as VoIP), especially in networks with a large number of routes. Prefixes are assigned to priority queues ("critical," "high," "medium," "low") based on route policy. This mechanism helps time-sensitive routes converge quickly.
Usage guidelines and limitations
The features support only IPv4 addresses.
-
To use multi-area interfaces, associate the loopback interface with an area of an ABR and reuse it as a multi-area interface elsewhere.
-
These features are limited to a single OSPF instance and a single VRF. Multiple instances or VRFs are not supported.
Feature introduction and release summary
| Feature Name | Release | Description |
|---|---|---|
| Limiting the Maximum Redistributed Type-3 LSA Prefixes in OSPF | Release 25.1.1 | Introduced on select fixed and modular systems; supported on 8712-MOD-M, 8011-4G24Y4H-I. |
| Limiting the Maximum Redistributed Type-3 LSA Prefixes in OSPF | Release 24.4.1 | Available on fixed (8200/8700) and modular (8800) systems; supported across additional models such as 8212-48FH-M, 8711-32FH-M, etc. |
| Limiting the Maximum Redistributed Type-3 LSA Prefixes in OSPF | Release 7.9.1 | Default limit set to 100,000 per process. Halts further redistribution and generates logs when exceeded. |
| Limiting LSA numbers in a OSPF Link-State Database | Release 25.1.1 | Enabled by default from 7.9.1. Limits nonself-generated LSAs to 500,000 per process; supported on key platforms. |
| Autonomous System Boundary Router Isolation and Adjacency Control | Release 25.1.1 | Provides protection by isolating ASBRs in LSA overload scenarios. |
| Autonomous System Boundary Router Isolation and Adjacency Control | Release 7.10.1 | Prevents traffic disruption during LSA overload by isolating ASBRs and controlling adjacency recovery. |
If only a high-priority route policy is configured, permitted prefixes are assigned to the high queue; unmatched prefixes (including /32s) are placed in the low-priority queue.
Example for configuring all /32s as medium priority:
-
prefix-set ospf-medium-prefixes
-
0.0.0.0/0 ge 32
-
end-set
Usage notes
Always configure route policies thoughtfully to align network priorities with traffic needs.
Peer routers must support OSPF protection features to prevent LSA leaks.
Use prefix suppression to reduce unnecessary route advertisements and bolster convergence and security.
Additional key behaviors
-
Overload protection: OSPF can disable adjacencies and log events if LSA or prefix limits are reached, preventing overall router instability.
-
ASBR isolation: When LSA limits are exceeded, neighboring routers can automatically isolate a misbehaving ASBR, keeping the rest of the OSPF domain operational.
-
Timers and thresholds: You can configure thresholds, ignore times, and recovery times for granular control over protection mechanisms.