OSPFv3: The Interface That Was Never Enabled
Two IPv6 routers, one process each, both with router IDs, and an empty neighbor table. Find the missing piece, live, right below.
Symptom
Both routers run OSPFv3 with valid router IDs and still never become neighbors. The process is fine. One interface was simply never told to join it.
Your mission
Inspect, recover, then verify
Format
Cisco IOS CLI
Investigate before you configure.
Use the CLI evidence to isolate the fault, make the smallest safe correction, then verify the network state changed.
Observe the symptom and link state.
Diagnose by comparing the protocol evidence.
Verify the expected device state and confirm the original symptom is resolved.
Console access: R1 · R2
This workspace stacks for portrait phones. Rotate to landscape for the full split-screen console.
Need a hint?
Reveal the root cause when you're ready.
Try the investigation first, then use this as your escape hatch, not a dead end.
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Lab debrief
Turn the session into a repeatable troubleshooting pattern.
Use this reference after your attempt: first explain the symptom, then verify the evidence, then confirm the repair.
The problem
R1 and R2 were migrated to IPv6 routing. Both show an OSPFv3 process with a router ID, both links are up/up with IPv6 addresses, and show ipv6 ospf neighbor is empty on both routers.
What you'll practice
- Read show ipv6 ospf neighbor on both ends of a link
- Compare which interfaces run OSPFv3 with show ipv6 ospf interface brief
- Enable OSPFv3 on an interface with ipv6 ospf 1 area 0
- Verify the adjacency and the learned IPv6 route
The topology
R1 and R2 share 2001:db8:12::/64 on Ethernet0/0, a broadcast segment, so they elect a DR and BDR. R2's Loopback0 is 2001:db8:2::2/128.
Commands to run yourself
The real diagnostic commands for this lab, copy-paste ready. Run these in the same order to reproduce the investigation on your own session.
show ipv6 ospf neighborshow ipv6 ospf interface briefshow ipv6 route ospfTopology diagram
Fact-checked references
The commands and behaviour in this lab were checked against these primary references.
Frequently asked
Why is there no error message?
Nothing is misconfigured from IOS's point of view. The process exists and the interface is healthy. The interface is simply not part of OSPFv3, so it sends no hellos and R1 never learns R2 exists.
Does OSPFv3 need an IPv4 router ID?
It needs a 32-bit router ID written like an IPv4 address. A router with IPv4 addresses picks one automatically, but an IPv6-only router cannot and needs router-id set by hand before the process will start.
Why FULL/BDR and not just FULL?
Ethernet is a broadcast network type, so OSPFv3 elects a designated router and a backup, exactly as OSPFv2 does. The part after the slash is the neighbor's role on that segment.
Ready to run this lab yourself?
No setup, no image sourcing. Book a session or ask for a live demo.