Configuring OSPF Hello Timer

The OSPF hello timer dictates the frequency at which an OSPF router sends hello packets to its OSPF neighbors. These hello packets help to verify the activity status of neighboring routers or to initiate a new neighbor relationship.
The OSPF hello interval varies depending on the OSPF network type. For Ethernet interfaces, the default OSPF hello interval is 10 seconds. However, this interval can be adjusted to suit specific network requirements.
A important rule regarding OSPF timers is that both OSPF routers attempting to establish a neighbor relationship must use the same timer value.
In this discussion, I’ll guide you through the process of configuring the OSPF hello timer. We’ll begin by examining the default OSPF hello timer setting and then change it to our preferred value.

Network Topology

The network topology we will be using in this post is depicted below. As you can see, it consists of two OSPF routers in OSPF Area 0. In this demonstration, we will configure OSPF on the two routers and then proceed to configure the OSPF hello timer on both routers.

Configuring OSPF Hello Timer

Here are steps to configure OSPF hello time on OSPF routers.

Step 1: Configure OSPF on the routers.

Firstly, let’s configure OSPF on R1 and R2 and advertise the connected network.

Router 1

R1(config)#interface ethernet0/0
R1(config-if)#ip address 192.168.12.1 255.255.255.0
R1(config-if)#no shutdown 
R1(config-if)#exit

R1(config)#router ospf 1
R1(config-router)#router-id 1.1.1.1
R1(config-router)#network 192.168.12.0 0.0.0.255 area 0
R1(config-router)#exit

Router 2

R2(config)#interface ethernet0/0
R2(config-if)#ip address 192.168.12.2 255.255.255.0
R2(config-if)#no shutdown
R2(config-if)#exit

R2(config)#router ospf 1
R2(config-router)#router
R2(config-router)#router-id 2.2.2.2
R2(config-router)#network 192.168.12.0 0.0.0.255 area 0
R2(config-router)#exit

Step 2: Check if both routers formed OSPF neighborship

Router 1

R1#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface
2.2.2.2           1   FULL/BDR        00:00:37    192.168.12.2    Ethernet0/0

Router 2

R2#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           1   FULL/DR         00:00:31    192.168.12.1    Ethernet0/0

Step 3: Check the default Hello Interval value on R2

As stated before, the default OSPF hello interval is 10s for ethernet interfaces.

R2#show ip ospf interface ethernet0/0

Ethernet0/0 is up, line protocol is up 
  Internet Address 192.168.12.2/24, Area 0, Attached via Network Statement
  Process ID 1, Router ID 2.2.2.2, Network Type BROADCAST, Cost: 10
  Topology-MTID    Cost    Disabled    Shutdown      Topology Name
        0           10        no          no            Base
  Transmit Delay is 1 sec, State BDR, Priority 1
  Designated Router (ID) 1.1.1.1, Interface address 192.168.12.1
  Backup Designated router (ID) 2.2.2.2, Interface address 192.168.12.2
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40       ^         ^
    Hello due in 00:00:06       ^         ^
  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 1.1.1.1  (Designated Router)
  Suppress hello for 0 neighbor(s)

 Step 4: Change the OSPF Hello interval on R2

Change the hello interval on R2 to 12 sec. Do the routers have neighborship with R1?

R2(config)#interface ethernet0/0
R2(config-if)#ip ospf hello-interval 12
R2(config-if)#exit

R2#show ip ospf interface ethernet0/0

Ethernet0/0 is up, line protocol is up 
  Internet Address 192.168.12.2/24, Area 0, Attached via Network Statement
  Process ID 1, Router ID 2.2.2.2, Network Type BROADCAST, Cost: 10
  Topology-MTID    Cost    Disabled    Shutdown      Topology Name
        0           10        no          no            Base
  Transmit Delay is 1 sec, State BDR, Priority 1
  Designated Router (ID) 1.1.1.1, Interface address 192.168.12.1
  Backup Designated router (ID) 2.2.2.2, Interface address 192.168.12.2
  Timer intervals configured, Hello 12, Dead 48, Wait 48, Retransmit 5
    oob-resync timeout 48       ^         ^
    Hello due in 00:00:04       ^         ^
  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 1.1.1.1  (Designated Router)
  Suppress hello for 0 neighbor(s)

Then check if R1 and R2 are still OSPF neighbor.

R2#show ip ospf neighbor
----> Empty <----

Step 5: Change the hello interval on R2 back to 10 sec

Change the hello interval on R2 back to 10 sec. Is the neighborship formed again?

R2(config)#interface ethernet0/0
R2(config-if)#ip ospf hello-interval 10
R2(config-if)#exit

R2#show ip ospf interface ethernet0/0

Ethernet0/0 is up, line protocol is up 
  Internet Address 192.168.12.2/24, Area 0, Attached via Network Statement
  Process ID 1, Router ID 2.2.2.2, Network Type BROADCAST, Cost: 10
  Topology-MTID    Cost    Disabled    Shutdown      Topology Name
        0           10        no          no            Base
  Transmit Delay is 1 sec, State DR, Priority 1
  Designated Router (ID) 2.2.2.2, Interface address 192.168.12.2
  Backup Designated router (ID) 1.1.1.1, Interface address 192.168.12.1
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40       ^	  ^
    Hello due in 00:00:08       ^	  ^
  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 0, maximum is 2
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 1, Adjacent neighbor count is 1 
    Adjacent with neighbor 1.1.1.1  (Backup Designated Router)
  Suppress hello for 0 neighbor(s)

Check whether the two routers have formed a neighborly relationship.

R2#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           1   FULL/BDR        00:00:31    192.168.12.1    Ethernet0/0

That is all for this post. Do check our the related content below;

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5. How to Configure OSPF Multi-Area
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