English

hello-interval (Protocols IS-IS)

date_range 13-Sep-17

Syntax

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hello-interval seconds;

Hierarchy Level

[edit logical-systems logical-system-name protocols isis interface interface-name level level-number],

[edit logical-systems logical-system-name routing-instances routing-instance-name protocols isis interface interface-name level level-number],

[edit protocols isis interface interface-name level level-number],

[edit routing-instances routing-instance-name protocols isis interface interface-name level level-number]

Release Information

Statement introduced before Junos OS Release 7.4.

Statement introduced in Junos OS Release 9.0 for EX Series switches.

Statement introduced in Junos OS Release 12.1 for the QFX Series.

Statement introduced in Junos OS Release 14.1X53-D20 for the OCX Series.

Description

Modify the frequency with which the routing device sends hello packets out of an interface, in seconds.

Routing devices send hello packets at a fixed interval on all interfaces to establish and maintain neighbor relationships. This interval is advertised in the hello interval field in the hello packet.

You can send out hello packets in subsecond intervals. To send out hello packets every 333 milliseconds, set the hold-time value to 1.

Options

seconds—Frequency of transmission for hello packets.

Range: 1 through 20,000 seconds

Default: 3 seconds (for designated intermediate system [DIS] routers), 9 seconds (for non-DIS routers)

Note

When elected as a designated intermediate system [DIS] router on any LAN adjacency, the hello and hold-timer intervals are scaled down by a factor of 3. This means the default values of 9 and 27 seconds of ISIS hello and hold time intervals are scaled down to 3 and 9 seconds for LAN adjacencies. During switchovers, this hello interval is too short to form LAN adjacencies. Therefore, you can configure one of the following solutions:

Set the hello and hold time interval for LAN adjacencies to 30 seconds and 90 seconds respectively on both the DIS and a neighboring router.
Convert the LAN interfaces to point-to-point IS-IS interfaces.

Best Practice

On QFX10000 switches, we strongly recommend that you configure all IS-IS interfaces, including peer interfaces, as point-to-point interfaces. If you do not, you might experience session flaps, that is, IS-IS sessions that go down and then come back up, when IS-IS is configured in virtual routing and forwarding (VRF) instances. When you scale IS-IS in any scenario, you might also experience scaling issues if you do not configure IS-IS interfaces as point-to-point interfaces.

Required Privilege Level

routing—To view this statement in the configuration.

routing-control—To add this statement to the configuration.