CCNA
December 22, 2019 Devices enable
OSPF constantly track the status of their neighbours, sending and receiving hello packet. Hello, packets show whether each neighbour still is functioning, and sending and receiving link-state advertisement and acknowledgment packets. OSPF sends hello packets and expects to receive Hello packets at particular intervals. The Hello and Dead Intervals timer is included in the
OSPF Hello messages. The OSPF Hello and Dead intervals are configurable values on a per-interface basis. We can check the current configured value using the “show ip ospf interface”
command. as shown in Figure 1. The GigabitEthernet 0/0 Hello and Dead intervals are set to the default 10 seconds and 40 seconds.  In Figure 2, the “show ip ospf neighbor” command is used on R1 to verify that R1 is adjacent to R2 and R3. The command is used subsequently several times. Notice that the output of the command illustrates the Dead Time is counting down from 40 seconds. By default, this value is refreshed every 10 seconds when R1 receives a Hello from the neighbours. Modifying OSPFv2 IntervalsSometimes we need to change the default Hello and Dead Intervals so that routers identify network failures in less time. Less timer’s increases traffic, but it reduces the convergence time. The default timer prepared for most of the network because it is based on best practices and should only be altered in rare situations. The Hello and Dead Intervals are configurable values in interface configuration modes.
We can reset the Hello Interval and Dead Intervals to their default values using the “no ip ospf hello-interval” and “no ip ospf dead-interval” commands. If we change the Hello interval to 5 seconds, immediately after changing the Hello interval, the Cisco IOS automatically change the Dead interval to four times the Hello interval. But it is not a good practice; it is always good to modify the timer manually. It is also important to modify the Hello and Dead Intervals on all adjacent routers because if alter one side of the OSPF link, when the Dead Timer expires on that router, it will lose the adjacency. The reason is that the values have only been changed on one side of the OSPF link. Therefore the OSPF Hello and Dead intervals must match between neighbours. Modifying OSPFv3 IntervalsWe can also modify and change the OSPFv3 intervals just like OSPFv2. We can modify the Hello and Dead Interval using the following interface configuration mode command.
Similarly to OSPFv2, we can restore the interval values to their default using the “no ipv6 ospf hello-interval” and “no ipv6 ospf dead-interval” commands. Similar to OSPFv2, if change the OSPFv3 Hello Interval to 5 seconds, Immediately after changing the Hello interval, the Cisco IOs automatically modifies the Dead interval to four times the Hello interval. However, it is also required to change the Dead interval manually to 20 seconds. We can verify using the “show ipv6 ospf neighbor command. The show ipv6 ospf interface command also be used to verify the Hello and Dead Intervals.
We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. By clicking “Accept”, you consent to the use of ALL the cookies. What is the default OSPF Hello interval in which hello packets are sent out on a broadcast multi access network?Hello interval.
The default is 10 seconds for broadcast and point-to point networks and 30 seconds for NBMA.
How often does OSPF send hello messages?Sending & Receiving OSPF Hello Messages. An OSPF router generates a Hello packet every poll interval -10 seconds for Peer-to-Peer (P2P) networks and 30 seconds for Non-Broadcast-Multiple-Access (NBMA) networks by default- and advertises it through multicast address 224.0.
What is the default value for the OSPF dead interval?Dead interval in seconds. Valid values range from 3 through 65535 seconds. The default is 40.
How do I find my OSPF Hello interval?To verify the Hello/Dead interval, use the show ip ospf interface command to display the details of OSPF enabled interfaces.
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