OSPF: Hello and Dead Timer Mismatch
A healthy link, matching areas, and an empty neighbor table with nothing in the log to explain it. Find the parameter that does not match, live, right below.
Symptom
Two routers share a subnet and the same area, but no adjacency ever forms. Compare the per-interface timers that must agree.
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.
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 are on the same transit subnet, in the same area, with matching masks and no authentication. show ip ospf neighbor is empty on both routers, and the remote LAN never appears in either routing table.
What you'll practice
- List the parameters that must match for an OSPF adjacency
- Read hello and dead intervals per interface
- Explain why timers are interface-level rather than process-level settings
- Align the timers and confirm the neighbor reaches FULL
1. List the parameters that must match for an OSPF adjacency
Area ID, hello and dead intervals, subnet and mask, authentication, stub flags, and MTU. Knowing the list turns a blank neighbor table into a short checklist rather than a guess.
2. Read hello and dead intervals per interface
show ip ospf interface reports both values for each participating interface, which is the only place a per-interface override is visible.
3. Explain why timers are interface-level rather than process-level settings
Changing a timer under router ospf is not possible, so an override applied to one interface affects only that link, which is exactly why the fault is so easy to overlook.
4. Align the timers and confirm the neighbor reaches FULL
You will watch the adjacency progress and confirm the previously missing route appears, rather than stopping at the configuration change.
The topology
Two routers connect over a single transit subnet, each with a LAN behind it that should be advertised into a single OSPF area.
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 ip ospf neighborshow ip ospf interface GigabitEthernet0/1show ip protocolsTopology diagram
Fact-checked references
The commands and behaviour in this lab were checked against these primary references.
Frequently asked
Will the routers log anything about the mismatch?
Not by default. Unlike a native VLAN mismatch, OSPF simply discards the hello packet whose timers do not match, so the symptom is an empty neighbor table with no explanatory message unless debugging is enabled.
Do I have to set both the hello and dead intervals?
Setting the hello interval automatically adjusts the dead interval to four times its value, so aligning hello on both ends usually resolves both. Verify the dead interval afterward, because an explicit override on either router persists.
Ready to run this lab yourself?
No setup, no image sourcing. Book a session or ask for a live demo.