Configures the hello interval, which is the length of time between the transmission of hello packets that this interface sends to neighbor routers. Show Syntaxip ospf hello-interval interval no ip ospf hello-interval Command DefaultThe default value is 10 seconds. ParametersintervalHello interval in seconds. Valid values range from 1 through 65535.ModesInterface subtype configuration mode Usage GuidelinesIf you change the hello interval, the dead interval is automatically changed to a value that is four times that of the new hello interval, unless the dead interval is also explicitly configured using the ip ospf dead-interval command. The recommended setting is that:
The running-config command displays only explicitly configured values of the dead interval, which means that a value that was automatically changed as the result of a hello-interval change is not displayed. The no form of the command restores the default value. ExamplesThe following example sets the hello interval to 50 on a specific OSPFv2 virtual Ethernet (VE) interface. To specify the interval between hello packets that the Cisco IOS software sends on the interface, use the “ip ospf hello-interval” command in interface configuration mode. To return to the default time, use the no form of this command. Ip ospf hello-interval seconds Examples Related- OSPF Interview Questions Dead IntervalIf an OSPF Layer 3 device does not receive a hello packet from a neighbor within a fixed time, the routing device understands that the neighbor is non-operational. The dead interval specifies the length of time, in seconds, that the routing device waits before declaring that a neighbor is unavailable. This is an interval during which the routing device receives no hello packets from the neighbor. This interval must be the same on all routing devices on a shared network. By default, this interval is four times the default hello interval, which is 40 seconds (broadcast and point-to-point networks) and 120 seconds (NBMA networks). Related- OSPF Neighbor States To set the interval at which hello packets must not be seen before neighbors declare the router down, use the “ip ospf dead-interval” command in interface configuration mode. To return to the default time, use the no form of this command. ip ospf dead-interval seconds Examples The following example sets the OSPF dead interval to 90 seconds:
Retransmit IntervalWhen OSPF sends an advertisement to an adjacent router, it expects to receive an acknowledgment from that neighbor. If no acknowledgment is received, the router will retransmit the advertisement to its neighbor. The retransmit-interval timer controls the number of seconds between retransmissions. To specify the time between link-state advertisement (LSA) retransmissions for adjacencies belonging to the interface, use the “ip ospf retransmit-interval” command in interface configuration mode. To return to the default value, use the no form of this command. ip ospf retransmit-interval seconds Examples The following example sets the retransmit interval value to 8 seconds: interface ethernet 2 OSPF Timers TypesBelow table enumerates the OSPF timers types and corresponding value in seconds on various Network types – OSPF routing devices constantly track the status of their neighbors, sending and receiving hello packets that indicate whether each neighbor still is functioning, and sending and receiving link-state advertisement (LSA) and acknowledgment packets. OSPF sends packets and expects to receive packets at specified intervals. You configure OSPF timers on the interface of the routing device participating in OSPF. Depending on the timer, the configured interval must be the same on all routing devices on a shared network (area). You can configure the following OSPF timers:
The default OSPF timer settings are optimal for most networks. However, depending on your network requirements, you might need to modify the timer settings. This example explains why you might need to modify the following timers:
Hello Interval and Dead Interval The hello interval and the dead interval optimize convergence times by efficiently tracking neighbor status. By lowering the values of the hello interval and the dead interval, you can increase the convergence of OSPF routes if a path fails. These intervals must be the same on all routing devices on a shared network. Otherwise, OSPF cannot establish the appropriate adjacencies. In the first example, you lower the hello interval to 2 seconds and the dead interval to 8 seconds on point-to-point OSPF interfaces fe-0/0/1 and fe-1/0/1 in area 0.0.0.0 by configuring the following settings:
LSA Retransmission Interval The link-state advertisement (LSA) retransmission interval optimizes the sending and receiving of LSA and acknowledgement packets. You must configure the LSA retransmission interval to be equal to or greater than 3 seconds to avoid triggering a retransmit trap because the Junos OS delays LSA acknowledgments by up to 2 seconds. If you have a virtual link, you might find increased performance by increasing the value of the LSA retransmission interval. In the second example, you increase the LSA retransmission timer to 8 seconds on OSPF interface fe-0/0/1 in area 0.0.0.1 by configuring the following setting:
Transit Delay The transit delay sets the time the routing device uses to age a link-state update packet. If you have a slow link (for example, one with an average propagation delay of multiple seconds), you should increase the age of the packet by a similar amount. Doing this ensures that you do not receive a packet back that is younger than the original copy. In the final example, you increase the transit delay to 2 seconds on OSPF interface fe-1/0/1 in area 0.0.0.1. By configuring the following setting, this causes the routing device to age the link-state update packet by 2 seconds:
Configuring the Hello Interval and the Dead Interval
CLI Quick ConfigurationTo quickly configure the hello and dead intervals, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, copy and paste the commands into the CLI at the [edit] hierarchy level, and then enter [edit] user@host# edit protocols ospf area 0.0.0.09 from configuration mode. [edit] set protocols ospf area 0.0.0.0 interface fe-0/0/1 hello-interval 2 set protocols ospf area 0.0.0.0 interface fe-0/0/1 dead-interval 8 set protocols ospf area 0.0.0.0 interface fe-1/0/1 hello-interval 2 set protocols ospf area 0.0.0.0 interface fe-1/0/1 dead-interval 8 Step-by-Step ProcedureTo configure the hello and dead intervals:
ResultsConfirm your configuration by entering the [edit protocols ospf area 0.0.0.0] user@host# set interface fe-0/0/1 user@host# set interface fe-1/0/12 command. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration. What are OSPF default hello and dead timers?The default values are 10 seconds for the hello time, and 40 seconds for the dead time. The usual rule of thumb with OSPF is to keep the dead time value four times the hello interval. However, this is not a strict rule.
What is the default value for the OSPF dead interval?The default value is 40 seconds (generally 4 times the hello packet interval). Specifies the time interval for the dead interval, in seconds.
What is hello interval and dead interval?Hello interval: this defines how often we send the hello packet. Dead interval: this defines how long we should wait for hello packets before we declare the neighbor dead.
How often are OSPF Hello packets sent by default on a broadcast network?By default, the routing device sends hello packets every 10 seconds (broadcast and point-to-point networks) and 30 seconds (nonbroadcast multiple access (NBMA) networks).
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