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The Link Monitor object allows you to monitor a link for a specific interface and belongs to a link detection group.

A new Link Monitor is created for each interface that is configured for link verification. The Link Monitor is provided with a destination to use for link verification as well as the Link Detection Group to which it belongs. The Link Monitor is responsible for pinging that destination, processing responses and determining when the interface should be considered failed. It reports such failures to its Link Detection Group. As a best practice, configure link monitors for the active and standby SBC with different destinations to avoid a failure scenario where the active and standby SBC fail back and forth due to link detection failures caused by loss of communication with a single destination. The active and standby SBC should be connected to different physical hardware (that is, switches) to avoid a single point of failure.

Each Link Monitor that is configured can also be configured with unique values for the Verify Timer, Response Timer, Reattempt Timer, and Maximum Retries. If configured, these values override the values configured for the Link Detection Group.

Each Link Monitor will set a timer while waiting to perform its next verification. The timeout for this timer is based on the configured Verify Timer value. When a ping is in progress and the Link Monitor is awaiting the response from the destination, a timer is set based on the configured Response Timer value. When the response times out and the Link Monitor retries, the Reattempt Timer value is used while waiting for the response.

When the number of consecutive failures reaches the Maximum Retries value, the Link Monitor considers the link verification as failed and reports this to its Link Detection Group.

While in the failed state, the Link Monitor will continue to attempt to ping the destination so that the failed condition can eventually clear. This is done at the rate specified by the Verify Timer.

The Link Monitor also supports a NULL destination (0.0.0.0), which disables the link verification for that interface. The interface is still considered failed if there is a hardware failure.

Link Monitor verifies transport on a specific interface via Layer 3 ICMP/ARP/NUD to a specific destination or monitors MII state for the physical port, where MII is defined as “Media Independent Interface”.

To View Link Monitor

On SBC main screen, go to Configuration > System Provisioning > Category: Base Provisioning > Link Detection Group > Link Monitor. The Link Monitor window is displayed.

Figure : Link Monitor

 

The Link Monitor can be checked for each Address Context or for each Link Detection Group or for all the Address Contexts and Link Detection Groups created. Use the drop-down box to select the desired Address Context and Link Detection Group.

Figure : Link Monitor Main Field

To Edit Link Monitor

To edit any of the Link Monitors in the list, click the radio button next to the specific Link Monitor name.

Figure : Link Monitor Highlighted

 

The Edit Selected Link Monitor window is displayed below.

Figure : Link Monitor Edit Window

 

Make the required changes and click Save at the right hand bottom of the panel to save the changes made.

To Create Link Monitor

To create a new Link Monitor, click New Link Monitor tab on the Link Monitor List panel.

Figure : Link Monitor Fields

 

The Create New Link Monitor window is displayed.

Figure : Link Monitor Create Window

 

 

The following fields are displayed:

Table : Link Monitor Parameters

 

Parameter

Description

Name

Specifies the name of this Link Monitor Group.

Physical Port

Physical port associated with the IP interface to be monitored. In a redundancy configuration, pkt0_p is paired with pkt0_s and pkt1_p is paired with pkt1_s.

  • pkt0_p – Primary packet 0 port.
  • pkt0_s – Secondary packet 0 port.
  • pkt1_p – Primary packet 1 port.
  • pkt1_s – Secondary packet 1 port.

This parameter is only visible on SBC 7000 systems.

Interface GroupSpecifies the name of the IP Interface Group to be monitored.
Interface

Specifies the name of the IP or management interface to be monitored.

IP or MGMT interface can be configured, depending on the type that is configured for the Link Detection Group.

Destination

Specifies the destination IP Address for link verification.

The Destination IP Address must be within the same subnet as the source interface.

Verify Timer

Specifies the time interval (in milliseconds) between the link verification attempts

Response Timer

Specifies the time to wait (in milliseconds) for a link verification attempt.

Reattempt
Timer

Specifies the time to wait (in milliseconds) for a link verification re-attempt.

Retries

Specifies the number of re-tries before the link verification is considered failed.

State

Specifies the administrative state for this link monitor.

Probe On Standby

Use this flag to enable/disable probing on the Standby port for the specified Link Monitor.

  • disabled – Use this option to disable probing on Standby port when the router does not respond properly to the ARP/NUD probes. For additional details, see "Link Detection Support" topic at SBC Redundancy.
  • enabled (default) – Use this option to allow probing on Standby port when the Link Monitor is configured for the Active port.

This flag is only visible on SBC 7000 systems and used when Router cannot reply to the ARP probe with a required unicast destination MAC address.

If the Link Detection Group takes precedence over Link Monitoring, delete the timers from the Link Monitor configuration. 

To Copy Link Monitor

To copy any of the created Link Monitor and to make any minor changes, click the radio button next to the specific Link Monitor to highlight the row.

Figure : Link Monitor Highlighted

 

Click Copy Link Monitor tab on the Link Monitor List panel.

Figure : Link Monitor Fields

 

The Copy Selected Link Monitor window is displayed along with the field details which can be edited.

Figure : Link Monitor Copy Window

 

 

Make the required changes to the required fields and click Save to save the changes. The copied Link Monitor is displayed at the bottom of the original Link Monitor in the Link Monitor List panel.

To Delete Link Monitor

To delete any of the created Link Monitor, click the radio button next to the specific Link Monitor which you want to delete.

Figure : Link Monitor Highlighted

 

Click Delete at the end of the highlighted row. A delete confirmation message appears seeking your decision.

Figure : Link Monitor Delete Confirmation

 

Click Yes to remove the specific Link Monitor from the list.