R0106-HP MSR Router Series Layer 2 - LAN Switching Configuration Guide(V7)
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The inner frame header for loop detection contains the following fields:
• Code—Protocol sub-type, which is 0x0001, indicating the loop detection protocol.
• Version—Protocol version, which is always 0x0000.
• Length—Length of the frame. The value includes the inner header, but excludes the Ethernet header.
• Reserved—This field is reserved.
Frames for loop detection are encapsulated as TLV triplets.
Table 8 TLVs supported by loop detection
TLV Description Remarks
End of PDU End of a PDU. Optional.
Device ID Bridge MAC address of the sending device. Required.
Port ID ID of the PDU sending port. Optional.
Port Name Name of the PDU sending port. Optional.
System Name Device name. Optional.
Chassis ID Chassis ID of the sending port. Optional.
Slot ID Slot ID of the sending port. Optional.
Sub Slot ID Sub-slot ID of the sending port. Optional.
Loop detection interval
Loop detection is a continuous process as the network changes. Loop detection frames are sent at a
specified interval (called a "loop detection interval") to check whether loops occur on ports and whether
loops are removed.
Loop protection actions
When the router detects a loop on a port, it generates a log but performs no action on the port by default.
You can configure the router to take one of the following actions:
• Block—Disables the port from learning MAC addresses and blocks inbound traffic to the port.
• No-learning—Disables the port from learning MAC addresses.
• Shutdown—Shuts down the port to disable it from receiving and sending any frames.
Port status auto recovery
When the router configured with the block or no-learning loop action detects a loop on a port, it
performs the action and waits three loop detection intervals. If the router does not receive a loop
detection frame within three loop detection intervals, it performs the following tasks:
• Automatically sets the port to the forwarding state.
• Notifies the user of the event.
When the router configured with the shutdown action detects a loop on a port, the following events
occur: