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Configuring Topologies and SPF Options for MT-OSPF

Include the following statements to enable topologies for OSPF and to configure topology identifiers. Any topologies you enable for OSPF must first be created under the [edit routing-options] hierarchy level. The routes for each topology are added to the routing table for the topology. For more information about the naming conventions for routing tables for topologies, see Routing Table Naming Conventions for Multitopology Routing.

The default topology is automatically created and has a topology identifier of 0 (zero), which cannot be modified. The routes that correspond to the default topology are added to the inet.0 routing table. You can, however, modify other parameters, such as shortest-path first (SPF) options. In addition, you can specify a topology for IPv4 multicast traffic. The topology for IPv4 multicast has a topology identifier of 1, which you cannot modify. The routes corresponding to this topology are added to the inet.2 routing table. You can also configure for each topology options for the SPF algorithm that override the default or globally configured SPF values. Include the following statements to configure a topology for OSPF and SPF options for the topology at the [edit protocols ospf] hierarchy level:



[edit protocols ospf]

topology (default
| ipv4-multicast | name) {

topology-id number;



spf-options {
delay milliseconds;
holddown milliseconds;
rapid-runs number;
}


}

For name, include the name of a topology that you configured under the [edit routing-options] hierarchy level to create the topology.

Use ipv4-multicast for IPv4 multicast traffic. You must first enable this topology under the [edit routing-options] hierarchy level.

topology-id number is the topology identifier. The range for topology-id number is from 32 through 127 for any topology you create, except for the default and IPv4 multicast topologies. The identifier for those topologies is predefined and cannot be modified.

Note: Multitopology Routing is not currently supported for OSPF version 3 (OSPFv3).

You can configure SPF options for each topology. The values you configure for each of the following options override the default or globally configured values.

The delay in the time between the detection of a topology change and when the SPF algorithm actually runs
The maximum number of times that the SPF algorithm can run in succession before the hold-down timer begins
The time to hold down, or wait, before running another SPF calculation after the SPF algorithm has run in succession the configured maximum number of times

To configure the SPF delay, include the delay statement when specifying the spf-options statement:



delay milliseconds;

By default, the SPF algorithm runs 200 milliseconds after the detection of a topology change. The range that you can configure is from 50 through 8000 milliseconds.

To configure the maximum number of times that the SPF algorithm can run in succession, include the rapid-runs statement when specifying the spf-options statement:



rapid-runs number;

The default number of SPF calculations that can occur in succession is 3. The range that you can configure is from 1 through 5. Each SPF algorithm is run after the configured SPF delay. When the maximum number of SPF calculations occurs, the hold-down timer begins. Any subsequent SPF calculation is not run until the hold-down timer expires.

To configure the SPF hold-down timer, include the holddown statement when specifying the spf-options statement:



holddown milliseconds;

The default is 5000 milliseconds, and the range that you can configure is from 2000 through 20,000 milliseconds. Use the hold-down timer to hold down, or wait, before running any subsequent SPF calculations after the SPF algorithm runs for the configured maximum number of times. If the network stabilizes during the hold-down period and the SPF algorithm does not need to run again, the system reverts to the configured values for the delay and rapid-runs statements.

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