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IPv6Global Config

ipv6 router ospf [pid]

Enables OSPFv3 routing process for IPv6 on a router and enters OSPF router configuration mode, used to configure OSPFv3 parameters.

Syntax·Global Config
ipv6 router ospf [pid]

When to Use This Command

  • Enable OSPFv3 on a router to route IPv6 traffic in an enterprise network.
  • Configure multiple OSPFv3 processes with different process IDs for administrative separation.
  • Set OSPFv3 router ID manually to ensure stability in router elections.
  • Adjust OSPFv3 timers like hello and dead intervals for faster convergence on high-speed links.

Command Examples

Basic OSPFv3 Configuration with Router ID

ipv6 router ospf 100
Router(config)# ipv6 router ospf 100
Router(config-rtr)# router-id 1.1.1.1
Router(config-rtr)# exit

The command enters OSPFv3 router configuration mode for process 100. The router-id command sets the OSPFv3 router ID to 1.1.1.1. The exit command returns to global configuration mode.

Verifying OSPFv3 Process Configuration

show ipv6 ospf 100
Routing Process "OSPFv3 (100)" with ID 1.1.1.1
Process uptime is 5 minutes
Supports only single TOS(TOS0) routes
It is an area border router
Number of areas: 2
  Area BACKBONE(0)
    Number of interfaces in this area is 2
    SPF algorithm executed 3 times
  Area 1
    Number of interfaces in this area is 1
    SPF algorithm executed 2 times

The output shows OSPFv3 process 100 with router ID 1.1.1.1. 'Process uptime' indicates how long the process has been running. 'It is an area border router' means this router connects to multiple areas. 'Number of areas' shows 2 areas: backbone (0) and area 1. For each area, the number of interfaces and SPF executions are listed.

Understanding the Output

The 'show ipv6 ospf [pid]' command displays OSPFv3 process details. The 'Routing Process' line shows the process ID and router ID. 'Process uptime' indicates stability. 'Supports only single TOS' is normal for OSPFv3. 'It is an area border router' appears if the router has interfaces in multiple areas. 'Number of areas' lists each area with its ID. For each area, 'Number of interfaces' shows how many interfaces are participating, and 'SPF algorithm executed' indicates how many times the SPF calculation has run (higher numbers may indicate network instability). Good values: low SPF counts, stable uptime. Watch for: frequent SPF recalculations indicating flapping links.

CCNA Exam Tips

1.

CCNA exam expects you to know that OSPFv3 uses a process ID that is locally significant and can be any value between 1 and 65535.

2.

Remember that OSPFv3 requires an explicit router-id command; if not configured, the router will use the highest IPv4 address on a loopback or physical interface.

3.

The exam may test that OSPFv3 runs directly over IPv6 (protocol 89) and does not rely on IPv4.

4.

Be aware that OSPFv3 uses link-local addresses for neighbor adjacencies, not global unicast addresses.

Common Mistakes

Forgetting to configure a router-id, which can cause OSPFv3 to fail to establish adjacencies if no IPv4 address is present.

Using the same process ID on multiple routers thinking it must match; process IDs are locally significant and can differ between routers.

Not enabling IPv6 unicast routing globally with 'ipv6 unicast-routing' before configuring OSPFv3, causing OSPFv3 to not start.

Related Commands

show ipv6 ospf

Displays general information about OSPFv3 (IPv6 OSPF) routing processes, including router ID, areas, and interfaces, used to verify OSPFv3 configuration and operation.

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