What is OSPF Hello/Dead Interval?

OSPF detects neighbors by means of Hello packets, and confirms that the neighbor is working properly by means of Hello packets. If OSPF sends Hello packets periodically and receives Hello packets from the neighbor, OSPF considers that the neighbor is working properly.

The interval at which Hello packets are sent is called the Hello interval, and the time at which the neighbor is considered to be down is the Dead interval.

Hello/Dead interval default

The Hello/Dead interval default is automatically determined by the network type. The default Hello/Dead interval for each network type is as follows

Network TypeHello interval(sec)Dead interval(sec)
Table Hello/Dead interval default

Since it is unlikely that the network type will be NON_BROADCAST/POINT_TO_MULTIPOINT, it is safe to assume that the default Hello/Dead interval is 10/40 (seconds).

By default, a Hello packet should be sent from the neighbor every 10 seconds. If no Hello packets are received from the neighbor for 40 seconds, the neighbor is considered to be down.

Hello/Dead interval configuration and verification commands

Configuring the Hello Interval

To change the Hello interval, enter the following command in interface configuration mode.

Configuring the Hello Interval

(config)#interface <interface-name>
(config-if)#ip ospf hello-interval <sec>

<interface-name> : interface name
<sec> : Hello interval(sec)

Changing the Hello interval will automatically change the Dead interval, which will be four times the value of the Hello interval you set.

Configuring Dead Interval

To change the Dead interval, enter the following command in interface configuration mode.

Configuring Dead Interval

(config)#interface <interface-name>
(config-if)#ip ospf dead-interval <sec>

<interface-name> : interface name
<sec> : Dead interval(sec)

The Dead interval value should be four times the Hello interval. If the Dead Interval is configured too short, it will not be possible to maintain the neighbor properly. Note that changing the Dead Interval does not automatically change the Hello Interval.

Set Dead interval to 1 second

To detect neighbor down in one second, set the Dead interval to one second. To do so, enter the following command in interface configuration mode.

Set Dead interval to 1 second

(config)#interface <interface-name>
(config-if)#ip ospf dead-interval minimal hello-multiplier <value>

<interface-name> : interface name
<value> : Number of Hello packets sent in one second.3-20

The value of is the number of Hello packets to be sent in one second. In other words, the interval for sending Hello packets is 1/ second.

Note on changing the Hello/Dead interval.

When changing the Hello/Dead interval, be sure to match it with the neighbor. One of the conditions for becoming a neighbor is that the Hello/Dead intervals match; if the Hello/Dead interval is changed on only one router, the neighbor condition will not be satisfied.

Verify the Hello/Dead interval.

To verify the Hello/Dead interval, use the show ip ospf interface command to display the details of OSPF enabled interfaces.

R1#show ip ospf interface FastEthernet 0/0
FastEthernet0/0 is up, line protocol is up
  Internet Address, Area 0
  Process ID 1, Router ID, Network Type BROADCAST, Cost: 1
  Transmit Delay is 1 sec, State BDR, Priority 1
  Designated Router (ID), Interface address
  Backup Designated router (ID), Interface address
  Flush timer for old DR LSA due in 00:02:48
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:07
  Supports Link-local Signaling (LLS)
  Index 1/1, flood queue length 0
  Next 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  (Designated Router)
  Suppress hello for 0 neighbor(s)

How the OSPF works