Unique Loop Detection
Unique Loop Detection
1. Function Overview
This product offers a proprietary system to detect whether there is a loop in the network environment that was configured.
This sends a proprietary loop detection frame from LAN/SFP ports and logical interfaces (hereinafter “loop detection-compatible interfaces”) to monitor whether that same frame returns or not.
If the transmitted frame returns, the system determines that there is a loop in the port in question.
2. Definition of Terms Used
LDF (Loop Detection Frame)
This is a Yamaha proprietary Ethernet frame that is used to detect loops.
3. Function Details
3.1. Loop detection operating specifications
The loop detection specifications for this product are shown below.
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The loop detection functionality in this product can be enabled/disabled for the entire system or for specific loop detection-compatible interfaces.
To activate loop detection at all loop detection-compatible interfaces, the loop detection function must be enabled for the entire system.-
Use the loop-detect command in global configuration mode for the system-wide setting.
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To activate loop detection at only specific loop detection-compatible interfaces, the loop-detect command must be used in the interface mode.
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The default settings for the loop detection function are as shown below. (In the initial state, this function is not operating.)
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System-wide setting: Disabled
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Setting for loop detection-compatible interfaces: Enabled
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If both loop detection and spanning tree protocol settings are set to enabled for the entire system, the spanning tree protocol is prioritized over the loop detection-compatible interface setting.
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If the loop detection function is enabled for this product, the following operations are performed.
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Loop detection frames (hereafter “LDF”) are sent every two seconds from linked-up loop detection-compatible interfaces.
However, the loop detection function is disabled at ports with mirroring specified (mirror ports). -
If an LDF sent from a port is received by that same port, a loop is determined to have occurred and the port that received the LDF performs the following actions.
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Port Shutdown
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If an LDF is sent and received at the same loop detection-compatible interface, the corresponding port is shut down.
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The linkup will be made five minutes after shutdown, and LDF transmission will resume. (If a loop has occurred, this operation will repeat.)
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When a linkup to the relevant port is desired within five minutes of monitored time, the no shutdown command is used.
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Port Blocking
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In any of the following cases, the port that received the LDF will block all non-LDF frames.
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An LDF sent from a logical interface was received at a LAN/SFP port
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An LDF sent from a static logical interface was received at an LACP logical interface
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Sending or receiving interfaces are the same type and the interface with the higher number received an LDF
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The LDF will be transmitted periodically, but LDF will not be forwarded from other devices.
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If a blocked loop detection-compatible interface does not detect an LDF sent from itself for 5 seconds, then the loop is considered resolved and normal communications are resumed.
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Port Detected
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In any of the following cases, the port that received the LDF will continue normal communications because other ports are blocked.
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An LDF sent from a LAN/SFP port was received at a logical interface
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An LDF sent from an LACP logical interface was received at a static logical interface
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Sending and receiving interfaces are the same type and the interface with the smaller number received an LDF
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When a loop is detected, the port lamp display on this product changes to a dedicated status, and the following SYSLOG message is output.
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[LOOP]: inf: Detected Loop! : port1.1, 1.3 … , sa1,3 …, po1,3 <1>
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The port lamp display on this product is restored as communications are resumed after the loop is resolved, and the following SYSLOG message is output.
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[LOOP]: inf: Recovered Loop! : port1.1, 1.3 … , sa1,3 …, po1,3 …
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Shutdown and blocking actions at loop detection-compatible interfaces that have detected a loop can be overridden to perform “loop detected” actions.
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Use the loop-detect blocking disable command for this setting.
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If this setting is “enabled”, port blocking will be implemented on the next largest port number. (Shutdown operations will not occur.)
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A force-clear can be performed on the loop detection status (detected, blocking) by using the loop-detect reset command. (On models equipped with a [MODE] button, this can be also done by holding down the [MODE] button for three seconds.)
If a linkdown has occurred on the port where a loop has been detected, the detection status will be cleared. (The port lamp display is restored, and the following syslog message is outputted.) -
The status of the loop detection function can be checked using the show loop-detect command. The following is displayed.
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System Enable/disable status
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Loop detection status display (status for a single loop detection-compatible interface)
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When an LDF is received by a loop detection-compatible interface when the loop detection function is disabled, frames received from all other ports will be forwarded as-is.
However, forwarding is disabled at ports with mirroring specified (mirror ports). -
In the following kinds of situations, loops in hubs that are connected to this product might not be detected.
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Loops are being detected in a connected hub
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Loop detection frames are not being forwarded by a connected hub
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3.2. Loop detection examples
The following shows examples of loop detection in this product.
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Loop detection examples
Loop detection case | Configuration example | Loop detection status |
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1 |
A loop is detected when a port receives the LDF that it has transmitted. |
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2 |
When loops are detected in multiple ports on the same terminal, the port with the largest number is blocked. |
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3 |
The loop is avoided by blocking multiple ports. |
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4 |
When loops are detected in multiple groups, the port with the largest number in each group |
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5 |
When a loop occurs between two switches, one of the switches detects the loop. |
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6 |
Out of the six ports that are connected by cable, the port for which the loop is most quickly detected is the one that is blocked. |
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7 |
Because the LDF transmitted from each port returns to these ports, port1.5 and port1.6 will both shut down. |
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8 |
Port1.6 of switch #B is blocked. |
4. Related Commands
Related commands are indicated below.
For details on the commands, refer to the Command Reference.
Operations | Operating commands |
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Enable/disable loop detection function (system) |
loop-detect enable/disable |
Enable/disable loop detection function (interface) |
loop-detect enable/disable |
Set port blocking for loop detection |
loop-detect blocking enable/disable |
Set port blocking duration time when a loop is detected |
loop-detect blocking interval |
Reset the loop detection status |
loop-detect reset |
Refer to the setting status of loop detection |
show loop-detect |
5. Examples of Command Execution
This example detects any loops occurring on this product using the following configuration, when the loop detection function is enabled.
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[Example 1] Loop occurring within this product
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[Example 2] Loop occurring in a third-party hub connected to this product
This sets LAN ports #1 and #3 to detect loops.
■ Setting Procedure
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Enable the loop detection function for the entire system.
Yamaha(config)#loop-detect enable (1)
1 Enable the loop detection function for the entire system -
Enable the loop detection function for LAN ports #1 and #3.
Yamaha(config)#interface port1.1 Yamaha(config-if)#spanning-tree disable (1) Yamaha(config-if)#loop-detect enable (2) Yamaha(config-if)#loop-detect blocking enable (3) (Also perform the above settings for LAN port #3.)
1 Disable the spanning tree function for each LAN port 2 Enable the loop detection function for each LAN port 3 Enables blocking -
The loop detection function for each LAN port and blocking are both enabled by default, so there is no need to set them.
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Confirm that the loop detection function has been set.
Confirm whether the loop detection function is enabled(*) for LAN ports #1 and #3.Yamaha>show loop-detect loop-detect: Enable port loop-detect port-blocking status ------------------------------------------------------- port1.1 enable(*) enable Normal port1.2 enable enable Normal port1.3 enable(*) enable Normal port1.4 enable enable Normal port1.5 enable enable Normal port1.6 enable enable Normal port1.7 enable enable Normal port1.8 enable enable Normal port1.9 enable enable Normal : : : : ------------------------------------------------------- (*): Indicates that the feature is enabled.
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If a loop has been detected, the loop detection status can be checked.
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In the case of example 1:
Yamaha>show loop-detect loop-detect: Enable port loop-detect port-blocking status ------------------------------------------------------- port1.1 enable(*) enable Detected (1) port1.2 enable enable Normal port1.3 enable(*) enable Blocking (2) port1.4 enable enable Normal port1.5 enable enable Normal port1.6 enable enable Normal port1.7 enable enable Normal port1.8 enable enable Normal port1.9 enable enable Normal : : : : ------------------------------------------------------- (*): Indicates that the feature is enabled.
1 LAN port #1 enters the detected status 2 LAN port #3 enters the blocking status -
In the case of example 2:
Yamaha>show loop-detect loop-detect: Enable port loop-detect port-blocking status ------------------------------------------------------- port1.1 enable(*) enable Shutdown (1) port1.2 enable enable Normal port1.3 enable(*) enable Normal port1.4 enable enable Normal port1.5 enable enable Normal port1.6 enable enable Normal port1.7 enable enable Normal port1.8 enable enable Normal port1.9 enable enable Normal : : : : ------------------------------------------------------- (*): Indicates that the feature is enabled.
1 LAN port #1 goes into the shutdown state
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6. Points of Caution
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All LAN/SFP ports included in the same logical interface must have the same loop detection setting (enabled, disabled, or blocked).
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LAN/SFP ports with different loop detection settings cannot be included in the same logical interface.
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Loop detection settings cannot be specified for LAN/SFP ports included in a logical interface.
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