ip ospf dead-interval [secs]
Sets the OSPF dead interval, which is the time a router waits to hear from a neighbor before declaring it down, used to tune OSPF convergence.
ip ospf dead-interval [secs]When to Use This Command
- Speeding up OSPF convergence on fast links by reducing the dead interval to 10 seconds.
- Matching the dead interval to a neighbor's configured interval to avoid adjacency flapping.
- Using a longer dead interval on unstable links to prevent unnecessary neighbor resets.
- Setting the dead interval to 4 times the hello interval as per OSPF default behavior.
Command Examples
Set dead interval to 40 seconds
ip ospf dead-interval 40Router(config-if)# ip ospf dead-interval 40 Router(config-if)#
No output is shown upon successful configuration. The command sets the OSPF dead interval to 40 seconds on the interface.
Verify dead interval with show ip ospf interface
show ip ospf interface GigabitEthernet0/0GigabitEthernet0/0 is up, line protocol is up
Internet Address 192.168.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 1.1.1.1, Interface address 192.168.1.1
Backup Designated router (ID) 2.2.2.2, Interface address 192.168.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:03
Supports Link-local Signaling (LLS)
Cisco NSF helper support enabled
IETF NSF helper support enabled
Index 1/1/1, flood queue length 0
Next 0x0(0)/0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2 (Backup Designated Router)
Suppress hello for 0 neighbor(s)The 'Timer intervals configured' line shows Hello 10, Dead 40. The Dead interval is 40 seconds, meaning the router will wait 40 seconds without receiving a hello from a neighbor before declaring it dead.
Understanding the Output
The primary command 'ip ospf dead-interval' does not produce output; it silently configures the interface. To verify, use 'show ip ospf interface'. In the output, look for 'Timer intervals configured' which lists Hello, Dead, Wait, and Retransmit intervals. The Dead interval is the time in seconds the router waits for a hello from a neighbor before considering the neighbor down. A typical default is 40 seconds (4 times the hello interval of 10 seconds). If the dead interval is set too low, neighbors may flap; if too high, convergence is slow. Ensure dead intervals match on both ends of a link to avoid adjacency issues.
CCNA Exam Tips
CCNA exam tip: The dead interval must match on both OSPF neighbors; otherwise, they will not form an adjacency.
CCNA exam tip: By default, dead interval is 4 times the hello interval (e.g., hello 10, dead 40).
CCNA exam tip: You can set the dead interval independently of the hello interval, but best practice is to keep the 4:1 ratio.
CCNA exam tip: On broadcast networks, the dead interval also affects the wait timer for DR/BDR election.
Common Mistakes
Mistake 1: Setting dead interval to a value lower than the hello interval, causing constant neighbor flapping.
Mistake 2: Forgetting to configure the same dead interval on both ends of a point-to-point link, preventing adjacency.
Mistake 3: Using 'ip ospf dead-interval' in global configuration mode instead of interface configuration mode.
Related Commands
ip ospf hello-interval [secs]
Configures the interval (in seconds) between OSPF Hello packets on an interface, used to adjust neighbor discovery and dead timer detection.
show ip ospf interface
Displays OSPF interface parameters and status, used to verify OSPF configuration and troubleshoot neighbor relationships.
show ip ospf neighbor
Displays OSPF neighbor information to verify adjacency formation and troubleshoot OSPF neighbor relationships.
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