Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 41)

Multi-Service IronWare Switching Configuration Guide 11
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Port loop detection
1
The following information applies to Strict Mode loop detection:
• A port is disabled only if a packet is looped back to that same port.
• Loop detection must be configured on the physical port.
• Strict Mode overcomes specific hardware issues where packets are echoed back to the input
port.
NOTE
Brocade recommends that you limit the use of Loose Mode. If you have a large number of VLANS or
VLAN groups, 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 Layer 2 loop prevention protocols, such as spanning tree (STP), the
Layer 2 protocol takes higher priority. Loop detection cannot send or receive probe packets if ports
are blocked by Layer 2 protocols, so it does not detect Layer 2 loops when STP is running because
loops within a VLAN have been prevented by STP. Loop detection running in Loose Mode can detect
and break Layer 3 loops because STP cannot prevent loops across different VLANs. In these
instances, the ports are not blocked and loop detection is able to send out probe packets in one
VLAN and receive packets in another VLAN. In this way, loop detection running in Loose Mode
disables both ingress and egress ports.
Enabling loop detection
Use the loop-detection command to enable loop detection on a physical port (Strict Mode) or a
VLAN (Loose Mode). Loop detection is disabled by default. The following example shows a Strict
Mode configuration.
Brocade(config)#interface ethernet 1/1
Brocade(config-if-e1000-1/1)#loop-detection
The following example shows a Loose Mode configuration.
Brocade(config)#vlan 20
Brocade(config-vlan-20)#loop-detection
The following example shows a Loose Mode configuration for a VLAN group.
Brocade(config)#vlan-group 10
Brocade(config-vlan-group-10)#add-vlan 1 to 100
Brocade(config-vlan-group-10)#loop-detection
By default, the port will send test packets every one second, or the number of seconds specified by
the loop-detection-interval command. Refer to
“Configuring a global loop detection interval.”
Syntax: [no] loop-detection
Use the [no] form of the command to disable loop detection.