Flap guard

A flapping port is a port that changes status rapidly from up to down. A flapping port can create instability in protocols such as STP. If a port is flapping, STP must continually recalculate the role for each port. Flap guard also prevents unwanted access to the physical ports.

The port flap guard detects how many times a port changes status during a specified number of seconds, and the system shuts down the port if necessary. You can manually reset the port and restore it to the active state.

This section covers the following topics:

• Retaining the triggered state
• Configuring the port flap guard
• Resetting a port
• Viewing the port flap guard configuration

Retaining the triggered state

When the flap guard is triggered, the status for the port is shown as “triggered” in the output of the diagnose flapguard status command. By default, rebooting the switch resets the state of the flap guard and removes the “triggered” state. You can change the setting so that the triggered state remains after a switch is rebooting until the port is reset. See Resetting a port.

Using the GUI:

1. Go to Switch > Flap Guard.
   
2. Select Retain Triggered State Across Reboot.
3. Select Update to save the change.

Using the CLI:

config switch global

set flapguard-retain-trigger enable

end

Configuring the port flap guard

The port flap guard is configured and enabled on each port. The default setting is disabled.

The flap rate counts how many times a port changes status during a specified number of seconds. The range is 1 to 30 with a default setting of 5.

The flap duration is the number of seconds during which the flap rate is counted. The range is 5 to 300 seconds with a default setting of 30 seconds.

The flap timeout (CLI only) is the number of minutes before the flap guard is reset. The range is 0 to 120 minutes. The default setting of 0 means that there is no timeout.

NOTE:

• If a triggered port times out while the switch is in a down state, the port is initially in a triggered state until the switch has fully booted up and calculated that the timeout has occurred.
• The following models do not store time across reboot; therefore, any triggered port is initially in a triggered state until the switch has fully booted up—at which point the trigger is cleared:
  • FS-1xxE
  • FS-2xxD/E
  • FS-4xxD
  • FS-4xxE

Using the GUI:

1. Go to Switch > Port > Physical.
2. Select a port.
3. Select Edit.
4. Under Flap Guard, select Enable.
   
5. Enter values for Flap Duration (Seconds) and Flap Rate.
6. Select Update to save the changes.

Using the CLI:

config switch physical-port

edit <port_name>

set flapguard {enabled | disabled}

set flap-rate <1-30>

set flap-duration <5-300 seconds>

set flap-timeout <0-120 minutes>

end

For example:

config switch physical-port

edit port10

set flapguard enabled

set flap-rate 15

set flap-duration 100

set flap-timeout 30

end

Resetting a port

After the flap guard detects that a port is changing status rapidly and the system shuts down the port, you can reset the port and restore it to service.

Using the GUI:

1. Go to Switch > Port > Physical.
2. Select the port that was shut down.
3. Select Reset.

Using the CLI:

execute flapguard reset <port_name>

For example:

execute flapguard reset port15

Viewing the port flap guard configuration

Use the following command to check if the flap guard is enabled on a specific port:

show switch physical-port <port_name>

For example:

show switch physical-port port10

Use the following command to display the port flap guard information for all ports:

diagnose flapguard status