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OSPF hello packet timers?

Networking Concepts IP Networking
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Question added by shahzad Ahmad , Network/ Database Administrator , Instaclear (PARCO)
Date Posted: 2014/04/23
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Lahbib SETTI
by Lahbib SETTI , System and Network Administrator , Global Axis - Saudi Bugshan Group

The HelloInterval and RouterDeadInterval are the two timers that you can adjust to speed up network convergence in an OSPF network. The HelloInterval determines the interval between sending OSPF Hello messages on an interface, while the RouterDeadInterval is the interval in which a router must receive an OSPF Hello message from a neighbor before it considers that neighbor to be down.

 

Cisco IOS assigns a default HelloInterval and RouterDeadInterval to OSPF enabled interfaces. Depending on the interface type, the HelloInterval will be either10 seconds or30 seconds. The RouterDeadInterval will be four times the HelloInterval (40 or120 seconds). A Cisco OSPF-enabled device will maintain a count down timer for each neighbor based on the RouterDeadInterval. Each time receives a Hello message from a neighbor, it will reset this timer to the RouterDeadInterval. If it does not receive a Hello message before this timer expires, then the neighbor will be set to the OSPF DOWN state.

 

You can adjust the HelloInterval and RouterDeadInterval with the ip ospf hello-interval and ip ospf dead-interval interface configuration commands. Doing so can reduce OSPF convergence, but you should be careful to take into consideration the quality (and possibly speed) of your links before doing so.

Deleted user
by Deleted user

The Hello and Dead timers must match to form a neighbor relationship in OSPF. Also when combining different OSPF network types such as point-to-point and point-to-multipoint you must adjust the timers to match as point-to-multipoint is30/120 by default and point-to-point is10/40 by default.

The dead-timer is typically four times the amount of the hello timer to give time for packet loss/drops due to network issues and/or quality of service policies.

 

To configure the hello timer, you’d use the: ip ospf hello-interval # whereas # is a number between1 and65535 seconds.

To configure the dead timer you’ll use the: ip ospf dead-interval # whereas # is a number between1 and65535 seconds.

To verify the OSPF timers on a particular interface you’ll use the :show ip ospf interface interfacename#/#.

Manoranjan Behera

Sending Hello packets         Hello packets are sent out each functioning router interface.         They are used to discover and maintain neighbor         relationships.[6] On broadcast and NBMA networks, Hello Packets         are also used to elect the Designated Router and Backup         Designated Router.         The format of an Hello packet is detailed in Section A.3.2.  The         Hello Packet contains the router's Router Priority (used in         choosing the Designated Router), and the interval between Hello         Packets sent out the interface (HelloInterval).  The Hello         Packet also indicates how often a neighbor must be heard from to         remain active (RouterDeadInterval).  Both HelloInterval and         RouterDeadInterval must be the same for all routers attached to         a common network...

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