19-10 ip ospf hi-interval seconds

19-10 ip ospf hello-interval seconds

Syntax Description:

• seconds ” The time in seconds between sending Hello packets over a link. The range of values is 1 “8192 seconds. The default value is 10 seconds (30 seconds on a nonbroadcast multiaccess [NBMA] network).

Purpose: OSPF Hello packets are used to initially establish the neighbor relationship. Once the neighbor relationship is established, the packets are used as a keepalive mechanism to determine if OSPF neighbors are active. The Hello interval should be less than the dead interval. All interfaces on a common network must have the same Hello interval or an OSPF neighbor relationship will not be established.

Initial Cisco IOS Software Release: 10.0

Configuration Example: Modifying the Interface Hello Interval

Configure the network in Figure 19-7 so you can observe the default timer values on an OSPF interface link. You will then experiment with adjusting the values of the Hello interval.

Figure 19-7. The Hello Interval Must Be Configured with the Same Value on All Interfaces Attached to a Common Network

 Router A  interface Loopback0   ip address 1.1.1.1 255.255.255.255   !   interface Serial0/1   ip address 10.1.1.1 255.255.255.252   clockrate 64000   !   router ospf 1   network 10.1.1.0 0.0.0.3 area 0   network 1.1.1.1 0.0.0.0 area 1  _________________________________________________________________ Router B  interface Loopback0   ip address 2.2.2.2 255.255.255.255   !   interface Serial0   ip address 10.1.1.2 255.255.255.252   !   router ospf 1   network 10.1.1.0 0.0.0.3 area 0   network 2.2.2.2 0.0.0.0 area 2  

View the timer values for the serial interface on Routers A and B.

 rtrA#  show ip ospf interface s0/1  Serial0/1 is up, line protocol is up   Internet Address 10.1.1.1/30, Area 0   Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1562   Transmit Delay is 1 sec, State POINT_TO_POINT,   Timer intervals configured,  Hello 10  , Dead 40, Wait 40, Retransmit 5     Hello due in 00:00:09   Index 1/2, flood queue length 0   Next 0x0(0)/0x0(0)   Last flood scan length is 1, maximum is 2   Last flood scan time is 0 msec, maximum is 4 msec   Neighbor Count is 1, Adjacent neighbor count is 1     Adjacent with neighbor 2.2.2.2   Suppress hello for 0 neighbor(s) _________________________________________________________________ rtrB#  show ip ospf interface serial 0  Serial0 is up, line protocol is up   Internet Address 10.1.1.2/30, Area 0   Process ID 1, Router ID 2.2.2.2, 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     Hello due in 00:00:09   Neighbor Count is 1, Adjacent neighbor count is 1     Adjacent with neighbor 1.1.1.1   Suppress hello for 0 neighbor(s) 

Notice that the default Hello interval is 10 seconds and the default dead interval is 40 seconds. Modify the configuration on Router A to change the Hello interval to 11 seconds while leaving the value for the Hello interval on Router B set to the default of 10 seconds.

 Router A  interface Serial0/1   bandwidth 64   ip address 10.1.1.1 255.255.255.252    ip ospf hello-interval 11    clockrate 64000  

Inspect the OSPF interface timers for serial 0/1 on Router A.

 rtrA#  show ip ospf interface serial 0/1  Serial0/1 is up, line protocol is up   Internet Address 10.1.1.1/30, Area 0   Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1562   Transmit Delay is 1 sec, State POINT_TO_POINT,   Timer intervals configured,  Hello 11, Dead 44  , Wait 44, Retransmit 5     Hello due in 00:00:05   Index 1/2, flood queue length 0   Next 0x0(0)/0x0(0)   Last flood scan length is 0, maximum is 2   Last flood scan time is 0 msec, maximum is 4 msec   Neighbor Count is 0, Adjacent neighbor count is 0   Suppress hello for 0 neighbor(s) 

The dead timer has been automatically set to four times the Hello interval.

Verify that Routers A and B have an OSPF neighbor relationship.

 rtrA#  show ip ospf neighbor  (no output) 

Because the Hello interval time on Router A does not match the Hello interval on Router B, an OSPF neighbor relationship will not be established. This can be seen by enabling OSPF debugging on Router B.

 rtrB#  debug ip ospf adj  OSPF adjacency events debugging is on rtrB# 17:03:20: OSPF: Rcv hello from 1.1.1.1 area 0 from Serial0 10.1.1.1 17:03:20: OSPF: Mismatched hello parameters from 10.1.1.1 17:03:20: Dead R 44 C 40, Hello R 11 C 10 

Modify the Hello interval on Router B to match the Hello interval on Router A.

 Router B  interface Serial0   ip address 10.1.1.2 255.255.255.252    ip ospf hello-interval 11   

Verification

Verify that the Hello interval on Router A matches the Hello interval on Router B.

 rtrB#  show ip ospf interface serial 0  Serial0 is up, line protocol is up   Internet Address 10.1.1.2/30, Area 0   Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64   Transmit Delay is 1 sec, State POINT_TO_POINT,   Timer intervals configured,  Hello 11, Dead 44  , Wait 44, Retransmit 5     Hello due in 00:00:07   Neighbor Count is 1, Adjacent neighbor count is 1     Adjacent with neighbor 1.1.1.1   Suppress hello for 0 neighbor(s) 

Verify that the OSPF neighbor relationship has been re-established.

 rtrB#  show ip ospf neighbor  Neighbor ID     Pri   State           Dead Time   Address         Interface 1.1.1.1           1   FULL/  -        00:00:42    10.1.1.1        Serial0 

Troubleshooting

Step 1. Verify that all interfaces attached to a common network are using the same value for the Hello interval.