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How Loopback Detection Works

Latest reply: Feb 25, 2021 05:45:27 147 12 4 0 0

After loopback detection is enabled on an interface, the interface sends a loopback detection packet every 5s by default. If a loopback detection packet is sent back to the interface, there is a loopback on the interface, indicating that a loop occurs on the network connected to the interface. Then the interface switches to the loopback detection state. The interface automatically restores to the previous status three detection intervals after the loop is removed.

You can configure the action performed on an interface when a loopback is detected, as shown in the following table.

Action

Description

Trap

Sends a trap.

Block

Sends a trap and blocks the   interface. The interface can be unblocked automatically.

Shutdown

Sends a trap and shuts down   the interface. The interface needs to be started manually.

Nolearning

Sends a trap and disables   MAC address learning on the interface. MAC address learning can be re-enabled   automatically.

After loopback detection is enabled on an interface, the interface sends untagged loopback detection packets by default. You can configure the interface to send loopback detection packets of a specified VLAN.

Various interfaces send loopback detection packets as follows:

  • Access interfaces and dot1q tunnel interfaces can      send only untagged loopback detection packets.

  • Trunk interfaces and hybrid interfaces can send      both untagged and tagged loopback detection packets. If a VLAN is      specified on a trunk or hybrid interface, the interface sends loopback      detection packets with the specified VLAN tag. A maximum of eight VLANs      can be specified on an interface. If an interface does not belong to the      specified VLAN, the interface does not send loopback detection packets      with the specified VLAN tag. If no VLAN is specified on an interface, the      interface sends untagged loopback detection packets.

Loopback detection cannot be configured on an Eth-Trunk or its member interfaces.

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user_3015189
Created Feb 22, 2021 19:22:04

Interesting post. Thanks for sharing How Loopback Detection Works-3805311-1
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lucian2003
lucian2003 Created Feb 23, 2021 02:04:46 (0) (0)
 
alexander.grosello
alexander.grosello Reply lucian2003  Created Feb 24, 2021 16:07:13 (0) (0)
 
wissal
MVE Author Created Feb 22, 2021 19:42:00

The content is beneficial
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lucian2003
lucian2003 Created Feb 23, 2021 02:05:05 (0) (0)
 
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NTan33
Created Feb 23, 2021 02:33:23

Another great explanation in a conveniently concise format.
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lucian2003
lucian2003 Created Feb 25, 2021 16:05:32 (0) (0)
Your welcome  
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DragonVN
Created Feb 24, 2021 03:28:27

Great. Thanks for sharing
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lucian2003
lucian2003 Created Feb 25, 2021 16:05:58 (0) (0)
Your welcome  
alexander.grosello
Author Created Feb 24, 2021 16:07:34

Thanks for sharing
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lucian2003
lucian2003 Created Feb 24, 2021 16:15:29 (0) (0)
your welcome  
Zebra
Created Feb 25, 2021 05:45:27

Thanks for sharing
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