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.
ip ospf hello-interval [secs]When to Use This Command
- Speed up OSPF convergence on a fast link by reducing the hello interval to 1 second.
- Match hello intervals on both sides of a link to ensure OSPF adjacency forms.
- Reduce OSPF overhead on a slow or congested WAN link by increasing the hello interval.
- Troubleshoot OSPF adjacency issues caused by mismatched hello intervals.
Command Examples
Set hello interval to 5 seconds on GigabitEthernet0/0
ip ospf hello-interval 5GigabitEthernet0/0 is up, line protocol is up
Internet address is 192.168.1.1/24
OSPF enabled on interface, area 0.0.0.0
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 5, Dead 20, Wait 20, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:03
Index 1/1, flood queue length 0
Next 0(0)/0(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 output shows OSPF interface details. The line 'Timer intervals configured, Hello 5, Dead 20, Wait 20, Retransmit 5' confirms the hello interval is set to 5 seconds. The dead interval (20 seconds) is automatically 4x the hello interval. 'Hello due in 00:00:03' indicates the next Hello packet will be sent in 3 seconds.
Set hello interval to 10 seconds on Serial0/0/0
ip ospf hello-interval 10Serial0/0/0 is up, line protocol is up
Internet address is 10.0.0.1/30
OSPF enabled on interface, area 0.0.0.0
Process ID 1, Router ID 1.1.1.1, Network Type POINT-TO-POINT, Cost: 64
Transmit Delay is 1 sec, State POINT-TO-POINT
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:07
Index 1/1, flood queue length 0
Next 0(0)/0(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
Suppress hello for 0 neighbor(s)On a point-to-point serial link, the hello interval is set to 10 seconds. The dead interval is 40 seconds (4x hello). The output shows the interface is in POINT-TO-POINT state with one adjacent neighbor. The 'Hello due in 00:00:07' shows the countdown to the next Hello.
Understanding the Output
The 'show ip ospf interface' command displays the configured hello interval in the line 'Timer intervals configured, Hello X, Dead Y'. The hello interval is the first number after 'Hello'. The dead interval is automatically set to 4 times the hello interval by default (unless manually changed). A shorter hello interval (e.g., 1 second) allows faster detection of neighbor failures but increases OSPF traffic. A longer interval (e.g., 30 seconds) reduces overhead but slows convergence. The 'Hello due in' field shows the time remaining until the next Hello packet is sent. If the hello interval is mismatched between neighbors, the adjacency will not form, and the 'Neighbor Count' will show 0. Always verify that the hello interval matches on both sides of a link.
CCNA Exam Tips
CCNA exam tip: The dead interval is automatically set to 4 times the hello interval unless manually changed with 'ip ospf dead-interval'.
CCNA exam tip: Hello intervals must match on both OSPF neighbors for adjacency to form; mismatched intervals prevent adjacency.
CCNA exam tip: On broadcast multiaccess networks (e.g., Ethernet), the default hello interval is 10 seconds; on non-broadcast networks (e.g., Frame Relay), it is 30 seconds.
CCNA exam tip: The 'ip ospf hello-interval' command is configured in interface configuration mode, not router OSPF mode.
Common Mistakes
Mistake: Setting the hello interval without also adjusting the dead interval manually, causing the dead interval to remain at 4x the new hello interval (which may be too short).
Mistake: Forgetting to apply the same hello interval on both ends of a link, resulting in OSPF adjacency not forming.
Mistake: Using the command in router OSPF configuration mode instead of interface configuration mode, which causes a syntax error.
Related Commands
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.
show ip ospf interface
Displays OSPF interface parameters and status, used to verify OSPF configuration and troubleshoot neighbor relationships.
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