Brocade Communications Systems 6650 Port loop detection

Brocade ICX 6650 Administration Guide 43

53-1002600-01

Basic port parameter configuration 2

Port loop detection

This feature allows the Brocade device to disable a port that is on the receiving end of a loop by

sending test packets. You can configure the time period during which test packets are sent.

There are two types of loop detection; Strict Mode and Loose Mode. In Strict Mode, a port is

disabled only if a packet is looped back to that same port. Strict Mode overcomes specific

hardware issues where packets are echoed back to the input port. In Strict Mode, loop detection

must be configured on the physical port.

In Loose Mode, loop detection is configured on the VLAN of the receiving port. Loose Mode

disables the receiving port if packets originate from any port or VLAN on the same device. The VLAN

of the receiving port must be configured for loop detection in order to disable the port.

Once a loop is detected on a port, it is placed in Err-Disable state. The port will remain disabled

until one of the following occurs:

•You manually disable and enable the port at the Interface Level of the CLI.

•You enter the command clear loop-detection. This command clears loop detection statistics

and enables all Err-Disabled ports.

•The device automatically re-enables the port. To set your device to automatically re-enable

Err-Disabled ports, refer to “Configuring the device to automatically re-enable ports” on

page4 4.

•Loopback detection packets are sent and received on both tagged and untagged ports.

Therefore, this feature cannot be used to detect a loop across separate devices.

The following information applies to Loose Mode loop detection:

•With Loose Mode, two ports of a loop are disabled.

•Different VLANs may disable different ports. A disabled port affects every VLAN using it.

•Loose Mode floods test packets to the entire VLAN. This can impact system performance if too

many VLANs are configured for Loose Mode loop detection.

NOTE

Brocade recommends that you limit the use of Loose Mode. If you have a large number of VLANS,

configuring loop detection on all of them can significantly affect system performance because of the

flooding of test packets to all configured VLANs. An alternative to configuring loop detection in a

VLAN-group of many VLANs is to configure a separate VLAN with the same tagged port and

configuration, and enable loop detection on this VLAN only.

NOTE

When loop detection is used with L2 loop prevention protocols, such as spanning tree (STP), the L2

protocol takes higher priority. Loop detection cannot send or receive probe packets if ports are

blocked by L 2 protocols , so it do es not dete ct L2 loop s when STP is runnin g because loops wi thin a

VLAN have been prevented by STP. Loop detection running in Loose Mode can detect and break L3