Configuration Guide User guide

66 FastIron Configuration Guide
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Basic port parameter configuration
• 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 L2 protocols, so it does not detect L2 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 L3
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)# vlan20
Brocade(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 66.
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.
Brocade(config)# loop-detection-interval 50