• 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 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.
device(config)# interface ethernet 1/1
device(config-if-e1000-1/1)# loop-detection
The following example shows a Loose Mode configuration.
device(config)# vlan20
device(config-vlan-20)# 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
on page 81.
Syntax:
[no] loop-detection
Use the [no] form of the command to disable loop detection.
Configuring a global loop detection interval
The loop detection interval specifies how often a test packet is sent on a port. When loop detection is
enabled, the loop detection time unit is 0.1 second, with a default of 10 (one second). The range is from
1 (one tenth of a second) to 100 (10 seconds). You can use the
show loop-detection status
command
to view the loop detection interval.
To configure the global loop detection interval, enter a command similar to the following.
device(config)# loop-detection-interval 50
This command sets the loop-detection interval to 5 seconds (50 x 0.1).
Enabling loop detection
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