Link Flap Prevention on Sx250 and Sx350 Switches
The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.
Objective
Link flap is a situation in which a physical interface on the switch continually goes up and down, three or more times a second for duration of at least 10 seconds. The common cause is usually related to bad, unsupported, or non-standard cable or Small Form-Factor Pluggable (SFP), or related to other link synchronization issues. The cause for link flapping can be intermittent or permanent. Link flap prevention mechanism minimizes the disruption to switch and network operation in a link flap situation. It stabilizes the network topology by automatically setting the ports that experience excessive link flap events to err-disable state ports. This mechanism also provides time to debug and locate root cause for flapping. A syslog message or Simple Network Management Protocol (SNMP) trap is sent to alert regarding link flap and port shutdown. The interface will become active again only if specifically enabled by the system administrator. This article provides instructions on how to enable the Link Flap Prevention feature, configure Automatic ErrDisable Recovery Time, and reactivate a suspended interface on your Sx250 or Sx350 Series Switch.
Applicable Devices
- SF350 Series
- SG350 Series
- SF250 Series
- SG250 Series
Software Version
- 2.1.0.63
Configure Link Flap Prevention
Enable Link Flap Prevention
Step 1. Log in to the web-based utility of your switch.
Step 2. In the Display Mode drop-down menu, choose Advanced.
Step 3. Choose Port Management > Port Settings.
Step 4. Check the Enable Link Flap Prevention check box.
Note: By default, the Link Flap Prevention feature is enabled.
Step 5. Click Apply to save changes to the running configuration file.
Step 6. Click Save to update the startup configuration file.
You should now have enabled Link Flap Prevention on your Sx350 Series Managed Switch.
Configure Automatic ErrDisable Recovery Time
Step 1. To set a recovery time for suspended interface, go to Port Management > Error Recovery Settings.
Step 2. (Optional) Enter a value in seconds in the Automatic Recovery Interval field.
Step 3. Under the Automatic ErrDisable Recovery area, check the Enable Link Flap Prevention check box.
Note: Link Flap Prevention is enabled by default for Automatic ErrDisable Recovery.
Step 4. Click Apply to save changes to the running configuration file.
Step 5. Click Save to update the startup configuration file.
You should now have configured the Automatic ErrDisable Recovery Time settings on your Sx350 Series Managed Switch.
Reactivate a Suspended Interface
Step 1. To check the status of errDisabled or suspended interface, go to Port Management > Error Recovery Settings.
Note: If an interface is suspended due to Link Flap Prevention, the Suspended (errDisabled) Interface Table will show the suspended interfaces.
Step 2. Check the check box next to the interface that you want to reactivate.
Step 3. Click the Reactivate button to reactivate a suspended interface.
You should now have reactivated a suspended interface on your Sx250 or Sx350 Series Managed Switch.
Enabling link flapping protection on an interface
Link flapping on an interface changes network topology and increases the system overhead. For example, in an active/standby link scenario, when interface status on the active link changes between UP and DOWN, traffic switches between active and standby links. To solve this problem, configure this feature on the interface.
With this feature enabled on an interface, when the interface goes down, the system enables link flapping detection. During the link flapping detection interval, if the number of detected flaps reaches or exceeds the link flapping detection threshold, the system shuts down the interface.
Configuration restrictions and guidelines
This feature takes effect only when it is configured in both the system view and interface view.
The dampening, link-delay, and port link-flap protect enable commands are mutually exclusive on an Ethernet interface.
To bring up an interface that has been shut down by link flapping protection, execute the undo shutdown command.
In the display interface command output, the Link-Flap DOWN value of the Current state field indicates that the interface has been shut down by link flapping protection.
Configuration procedure
To enable link flapping protection on an interface:
Configure Link Flap Prevention on a Cisco Business Switch using CLI
The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.
Objective
Link flap is a situation in which a physical interface on the switch continually goes up and down, three or more times a second for duration of at least 10 seconds. The common cause is usually related to bad, unsupported, or non-standard cable or Form-Factor Pluggable (SFP), or related to other link synchronization issues. The cause for link flapping can be intermittent or permanent. Link flap prevention mechanism minimizes the disruption to switch and network operation in a link flap situation. It stabilizes the network topology by automatically setting the ports that experience excessive link flap events to err-disable state ports. This mechanism also provides time to debug and locate root cause for flapping. A syslog message or Simple Network Management Protocol (SNMP) trap is sent to alert regarding link flap and port shutdown. The interface will become active again only if specifically enabled by the system administrator. This article provides instructions on how to enable the Link Flap Prevention feature, configure Automatic ErrDisable Recovery settings, and reactivate a suspended interface through the Command Line Interface (CLI) of the switch.
Applicable Devices | Software Version
- CBS250 (Data Sheet) | 3.1.0.57 (Download latest)
- CBS350 (Data Sheet) | 3.1.0.57 (Download latest)
- CBS350-2X (Data Sheet) | 3.1.0.57 (Download latest)
- CBS350-4X (Data Sheet) | 3.1.0.57 (Download latest)
Configure Link Flap Prevention Settings
Enable Link Flap Prevention
Step 1
Log in to the switch console. The default username and password is cisco/cisco. If you have configured a new username or password, enter the credentials instead.
To learn how to access a Cisco Business Switch CLI through SSH or Telnet, click here.
The commands may vary depending on the exact model of your switch.
Step 2
From the Privileged EXEC mode of the switch, enter the Global Configuration mode by entering the following:
Step 3
To globally enable setting a physical interface to err-disable state due to excessive link flapping, enter the following:
CBS350(config)# link-flap prevention [enable | disable]
This command will shut down the Ethernet (physical) interfaces if the interface experienced three link flaps (link status changes) within each second for a duration of 10 seconds.
Step 4
(Optional) To disable link flap prevention on the switch, enter the following:
CBS350(config)# no link-flap prevention
Step 5
(Optional) To enable jumbo frames on the switch, enter the following:
CBS350(config)# port jumbo-frame
You have now successfully configured the Link Flap Prevention settings on your switch through the CLI.
Configure Automatic ErrDisable Recovery Settings
To enable the function of automatically reactivating a port that has been shut down because of an error condition after the Automatic Recovery Interval has passed, follow these steps:
Step 1
In the Global Configuration mode, enter the Interface Configuration context by entering the following:
- link-flapping — Enables the error recovery mechanism for the link-flap prevention Err-Disable state.
Step 2
To set the error recovery timeout interval of the errdisable recovery, enter the following:
- seconds — Specifies the error recovery timeout interval in seconds. The range is from 30 to 86400 seconds. The default value is 300 seconds.
Step 3
Enter the exit command to go back to the Privileged EXEC mode:
You have now successfully configured the automatic errdisable recovery settings on your switch through the CLI.
Reactivate a Suspended Interface
To manually reactivate an interface that was shut down, follow the steps:
Step 1
To activate an interface that was configured to be active but was shut down by the system, enter the following:
CBS350# set interface active [interface-id]
Step 2
(Optional) In the Privileged EXEC mode of the switch, save the configured settings to the startup configuration file by entering the following:
CBS350# copy running-config startup-config
Step 3
(Optional) Press Y for Yes or N for No on your keyboard once the Overwrite file [startup-config]. prompt appears.
You have now successfully reactivated a suspended interface on your switch through the CLI.
Включение функции D-Disable Link-Flap на MES5448/MES7048
Данный функционал позволяет переводить порт в статус errdisable при флапинге линка.
Функционал включается следующей командой:
console(Config)# link-flap d-disable
По умолчанию время которое необходимо для фиксирования флапинга линка и последующего перевода его в errdisable равно 10 секундам, за это время должно произойти 5 флапов. Изменить данные значение можно при помощи команд:
console(Config)# link-flap d-disable duration
console(Config)# link-flap d-disable max-count
Включение функционала errdisable, для автоматического восстановления линка после перехода в состояние errdisable:
console(Config)# errdisable recovery cause link-flap
- Нет меток