In which configuration mode is show ipv6 ospf used?

The show ipv6 ospf command is entered in Privileged EXEC mode on Cisco IOS devices.

IPv6Privileged EXEC

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.

Definition: show ipv6 ospf is a Cisco IOS privileged exec command. Displays general information about OSPFv3 (IPv6 OSPF) routing processes, including router ID, areas, and interfaces, used to verify OSPFv3 configuration and operation.

Overview

The 'show ipv6 ospf' command is a fundamental diagnostic tool for OSPFv3 (Open Shortest Path First version 3) in IPv6 networks. It provides a high-level summary of the OSPFv3 routing process, including the router ID, OSPF process ID, areas configured, and interfaces participating in OSPFv3. This command is essential for verifying that OSPFv3 is properly configured and operational, and it serves as the first step in troubleshooting OSPFv3 adjacency issues, route propagation problems, or area design misconfigurations.

Unlike its IPv4 counterpart 'show ip ospf', which displays similar information for OSPFv2, 'show ipv6 ospf' focuses exclusively on the IPv6 OSPF process. Network engineers reach for this command when they need to confirm that OSPFv3 is running, check the router ID (which is derived from an IPv4 address even in IPv6-only networks), verify the OSPF process ID, and see which interfaces are enabled for OSPFv3. It also shows the number of areas, the area types (normal, stub, NSSA), and the number of interfaces in each area.

This command is particularly useful during initial OSPFv3 deployment, after configuration changes, or when troubleshooting connectivity issues between IPv6 networks. The output is buffered and may be truncated if the terminal length is not set appropriately; using 'terminal length 0' before the command ensures the full output is displayed. The command requires privileged EXEC mode (enable) and does not modify the running configuration.

It fits into the broader workflow of OSPFv3 verification, often used before more detailed commands like 'show ipv6 ospf neighbor' or 'show ipv6 ospf interface'. Understanding the output helps engineers quickly assess the health of the OSPFv3 process and identify potential issues such as a missing router ID, incorrect area assignment, or interfaces not participating in OSPFv3. The command also displays the OSPFv3 process uptime, which can indicate recent restarts or flapping.

In summary, 'show ipv6 ospf' is a critical command for any engineer working with OSPFv3, providing a concise yet comprehensive view of the OSPFv3 routing process.

Syntax·Privileged EXEC

show ipv6 ospf

When to Use This Command

Verify OSPFv3 process is running and check router ID after initial configuration.
Troubleshoot OSPFv3 neighbor adjacency issues by reviewing active interfaces and areas.
Check OSPFv3 redistribution and routing table references.
Monitor OSPFv3 SPF statistics and timer values for performance tuning.

Parameters

Parameter	Syntax	Required	Description
process-id	<1-65535>	Optional	Specifies the OSPFv3 process ID to display information for. If omitted, information for all OSPFv3 processes is shown. Common mistake: using a process ID that does not exist on the router, resulting in no output.

Command Examples

Basic OSPFv3 Process Information

show ipv6 ospf

Routing Process "OSPFv3 (1)" with ID 192.168.1.1
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x000000
Number of AS-scoped unknown LSA 0
Number of LSA originated 10
Number of LSA received 5
Number of areas in this router is 2. 2 normal 0 stub 0 nssa
Area BACKBONE(0)
    Number of interfaces in this area is 2
    SPF algorithm executed 4 times
    Number of LSA 5. Checksum Sum 0x02B3F1
Area 1
    Number of interfaces in this area is 1
    SPF algorithm executed 3 times
    Number of LSA 3. Checksum Sum 0x01A2C4

Line 1: OSPFv3 process number (1) and router ID (192.168.1.1). Line 2: Indicates this router is an ABR (Area Border Router). Lines 3-4: SPF and LSA timing parameters. Lines 5-8: Counts of external and unknown LSAs, and originated/received LSAs. Line 9: Total number of areas (2) and their types. Lines 10-15: Area BACKBONE(0) details: 2 interfaces, SPF run count, LSA count and checksum. Lines 16-19: Area 1 details: 1 interface, SPF runs, LSA count.

OSPFv3 with Virtual Links and Filtering

show ipv6 ospf

Routing Process "OSPFv3 (10)" with ID 10.0.0.1
It is an internal router
SPF schedule delay 1 secs, Hold time between two SPFs 5 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 2. Checksum Sum 0x001234
Number of AS-scoped unknown LSA 0
Number of LSA originated 15
Number of LSA received 12
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Area 0
    Number of interfaces in this area is 3
    SPF algorithm executed 10 times
    Number of LSA 8. Checksum Sum 0x045678
    Virtual link to router ID 192.168.2.1 is up

Line 1: OSPFv3 process 10, router ID 10.0.0.1. Line 2: Internal router (not ABR/ASBR). Lines 3-4: Faster SPF timers (delay 1s, hold 5s). Lines 5-8: External LSAs present (2), LSA counts. Line 9: Single area (normal). Lines 10-14: Area 0 with 3 interfaces, SPF executed 10 times, LSA count. Line 15: Virtual link to router 192.168.2.1 is operational (important for non-contiguous area 0).

Understanding the Output

The 'show ipv6 ospf' command provides a summary of the OSPFv3 routing process. Key fields: 'Routing Process' shows process ID and router ID (a 32-bit number, often an IPv4 address). 'It is an area border router' or 'internal router' indicates router role; ABR connects multiple areas, ASBR redistributes external routes.

SPF schedule delay and hold time affect convergence speed; default values are 5 and 10 seconds. LSA counts help detect instability: rapidly increasing LSA numbers may indicate flapping routes. 'Number of areas' shows area count and types (normal, stub, NSSA).

For each area, 'Number of interfaces' indicates OSPFv3-enabled interfaces; if zero, check interface configuration. 'SPF algorithm executed' count rises with topology changes; frequent SPF runs suggest instability. 'Virtual link' status (if present) shows connectivity to backbone area.

Good values: router ID unique, SPF runs stable, LSA counts consistent. Bad values: router ID 0.0.0.0 (not set), zero interfaces in an area, or virtual link down.

Configuration Scenarios

Verify OSPFv3 Configuration on a Single Router

After configuring OSPFv3 on a router, you need to confirm that the process is running, the router ID is set, and interfaces are participating in the correct areas.

Topology

R1(Gi0/0)---10.0.12.0/30---(Gi0/0)R2
R1(Gi0/1)---2001:db8:1:1::/64---PC1

Steps

1.Step 1: Enter privileged EXEC mode: enable
2.Step 2: Run the command: show ipv6 ospf
3.Step 3: Verify the output shows the OSPFv3 process ID, router ID, and interfaces.

Configuration

! OSPFv3 configuration on R1
ipv6 unicast-routing
interface GigabitEthernet0/0
 ipv6 address 2001:db8:12::1/64
 ipv6 ospf 1 area 0
!
interface GigabitEthernet0/1
 ipv6 address 2001:db8:1:1::1/64
 ipv6 ospf 1 area 1
!
ipv6 router ospf 1
 router-id 1.1.1.1
!

Verify: Expected output snippet: Routing Process "OSPFv3 (1)" with ID 1.1.1.1 Supports only single TOS(TOS0) routes It is an autonomous system boundary router Redistributing External Routes from, Number of areas in this router is 2. 2 normal 0 stub 0 nssa Area BACKBONE(0) Number of interfaces in this area is 1 SPF algorithm executed 3 times Area (1) Number of interfaces in this area is 1 SPF algorithm executed 2 times

Watch out: If the router ID is not manually configured, OSPFv3 will use the highest IPv4 address on a loopback interface. If no IPv4 address exists, the OSPFv3 process may not start. Always configure a router-id under the OSPFv3 process.

Troubleshoot OSPFv3 Process Not Starting

After configuring OSPFv3, the process does not start, and no OSPFv3 routes appear. The 'show ipv6 ospf' command returns no output or an error.

Topology

R1(Gi0/0)---2001:db8:12::/64---(Gi0/0)R2

Steps

1.Step 1: Check if IPv6 unicast routing is enabled: show ipv6 interface brief
2.Step 2: Verify OSPFv3 configuration: show running-config | section ipv6 router ospf
3.Step 3: Ensure a router ID is configured: show ipv6 ospf
4.Step 4: If no output, check if the OSPFv3 process exists: show ipv6 ospf ?

Configuration

! Correct OSPFv3 configuration
ipv6 unicast-routing
!
ipv6 router ospf 1
 router-id 1.1.1.1
!
interface GigabitEthernet0/0
 ipv6 address 2001:db8:12::1/64
 ipv6 ospf 1 area 0
!

Verify: After fixing, 'show ipv6 ospf' should display the OSPFv3 process information. If the process is missing, ensure 'ipv6 unicast-routing' is enabled globally.

Watch out: A common mistake is forgetting to enable 'ipv6 unicast-routing' globally. Without it, OSPFv3 will not start, and 'show ipv6 ospf' will return no output.

Troubleshooting with This Command

When troubleshooting OSPFv3 issues, 'show ipv6 ospf' is the first command to run. Healthy output shows the OSPFv3 process ID, router ID, and a list of areas with interfaces. Key indicators of problems include: no output (process not running), missing router ID (process may not start), or areas with zero interfaces (interfaces not enabled for OSPFv3).

Focus on the 'Number of areas' line: if it shows 0 areas, no interfaces are participating. Also check the 'SPF algorithm executed' count; if it is very high, the network may be unstable. Common symptoms this command helps diagnose include: OSPFv3 not forming adjacencies (check if interfaces are listed in the correct area), routes not being learned (verify that the process is running and areas are correct), and router ID conflicts (if two routers have the same router ID, adjacencies may fail).

A step-by-step diagnostic flow: 1) Run 'show ipv6 ospf' to confirm the process is running. If no output, check 'ipv6 unicast-routing' and OSPFv3 configuration. 2) Verify the router ID is set; if not, configure it. 3) Check that interfaces appear under the correct area. If an interface is missing, verify the 'ipv6 ospf' command on the interface. 4) If areas are correct but adjacencies are not forming, proceed to 'show ipv6 ospf neighbor' and 'show ipv6 ospf interface'.

Correlate 'show ipv6 ospf' output with 'show ipv6 route ospf' to see if routes are being installed. Use 'debug ipv6 ospf events' for real-time adjacency issues, but be cautious in production. The command output also shows whether the router is an ASBR (autonomous system boundary router) or ABR (area border router), which is important for redistribution and area design.

In summary, 'show ipv6 ospf' provides a quick health check of the OSPFv3 process and guides further troubleshooting steps.

CCNA Exam Tips

CCNA exam may ask to identify the OSPFv3 router ID from the output; it is always a 32-bit number, often an IPv4 address even in IPv6 OSPF.

Know that 'show ipv6 ospf' does not show neighbors; use 'show ipv6 ospf neighbor' for adjacency details.

The output indicates if a router is an ABR or internal; exam scenarios may test understanding of area border roles.

Be able to interpret SPF timer values and LSA counts to diagnose network stability issues.

Common Mistakes

Confusing OSPFv3 (IPv6) with OSPFv2 (IPv4); the command is 'show ipv6 ospf' not 'show ip ospf'.

Assuming 'show ipv6 ospf' shows neighbor details; it only shows process and area info.

Overlooking the router ID; if it is 0.0.0.0, OSPFv3 is not properly configured.

Misinterpreting 'Number of areas' as number of interfaces; it is the count of configured areas.

show ipv6 ospf vs ping ipv6 [address]

Both 'show ipv6 ospf' and 'ping ipv6 [address]' are IPv6-related commands used in troubleshooting, but they serve fundamentally different purposes. 'show ipv6 ospf' reveals OSPFv3 process and neighbor state, while 'ping ipv6' tests end-to-end reachability. They are often confused because both help diagnose IPv6 routing issues, yet one examines the routing protocol itself and the other verifies actual connectivity.

Aspect	show ipv6 ospf	ping ipv6 [address]
Scope	OSPFv3 process and neighbor status	End-to-end IPv6 connectivity
Output type	Structured process and interface details	Echo reply statistics
Protocol layer	Layer 3 (routing protocol)	Layer 3 (ICMPv6)
Configuration dependency	Requires OSPFv3 configured	Requires IPv6 connectivity
Troubleshooting focus	Routing protocol health	Path availability

Use show ipv6 ospf when you need to verify OSPFv3 adjacencies, check router ID, or confirm that OSPFv3 is running on the correct interfaces.

Use ping ipv6 [address] when you want to test whether a specific IPv6 destination is reachable and measure round-trip time or packet loss.

Platform Notes

In IOS-XE, the 'show ipv6 ospf' command syntax and output are identical to classic IOS. However, in IOS-XE 16.x and later, the output may include additional fields such as 'Graceful restart' information. On NX-OS, the equivalent command is 'show ip ospfv3' (note the 'v3' instead of 'ipv6').

The NX-OS output is similar but may have different formatting and includes process details like 'OSPFv3 Process ID'. On ASA firewalls, OSPFv3 is not supported; only OSPFv2 is available. For IOS-XR, the command is 'show ospfv3' (without 'ipv6'), and the output is significantly different, focusing on process and area details in a structured format.

In older IOS versions (12.x), the command may not support certain parameters like 'process-id' filtering; it shows all processes by default. In 15.x and 16.x, the command is fully featured. When using the command on a switch running IOS, the output is the same as on routers.

Always ensure the device supports IPv6 and OSPFv3; some older switches may not. For automation, the command output can be parsed using 'show ipv6 ospf | include' to extract specific lines. In summary, while the command is consistent across IOS platforms, engineers should be aware of the slight syntax differences on NX-OS and IOS-XR.

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