HP 3600 v2 series Configuration Manual page 105

Enabling loop guard
A device that keeps receiving BPDUs from the upstream device can maintain the state of the root port and
blocked ports. However, link congestion or unidirectional link failures might cause these ports to fail to
receive BPDUs from the upstream devices. The device will reselect the port roles: Those ports in
forwarding state that failed to receive upstream BPDUs will become designated ports, and the blocked
ports will transition to the forwarding state, resulting in loops in the switched network. The loop guard
function can suppress the occurrence of such loops.
The initial state of a loop guard-enabled port is discarding in every MSTI. When the port receives BPDUs,
its state transitions normally. Otherwise, it stays in the discarding state to prevent temporary loops.
Configure loop guard on the root port and alternate ports of a device.
Follow these steps to enable loop guard:
To do...
Enter system view
Enter interface
view or port
group view
Enable the loop guard function for the ports
NOTE:
Do not enable loop guard on a port that connects user terminals. Otherwise, the port will stay in the
•
discarding state in all MSTIs because it cannot receive BPDUs.
You cannot configure edge port settings and loop guard, or configure root guard and loop guard on a
•
port at the same time.
Enabling TC-BPDU guard
When a switch receives topology change (TC) BPDUs (the BPDUs that notify devices of topology
changes), the switch flushes its forwarding address entries. If someone forges TC-BPDUs to attack the
switch, the switch will receive a large number of TC-BPDUs within a short time and be busy with
forwarding address entry flushing. This affects network stability.
With the TC-BPDU guard function, you can set the maximum number of immediate forwarding address
entry flushes that the device can perform every a specified period of time (10 seconds). For TC-BPDUs
received in excess of the limit, the device performs a forwarding address entry flush when the time period
expires. This prevents frequent flushing of forwarding address entries.
Follow these steps to enable TC-BPDU guard:
To do...
Enter system view
Enable the TC-BPDU guard function
Configure the maximum number of
forwarding address entry flushes that the
device can perform every 10 seconds
Enter Layer 2 Ethernet
interface view or Layer 2
aggregate interface view
Enter port group view
Use the command...
system-view
interface interface-type
interface-number
port-group manual
port-group-name
stp loop-protection
Use the command...
system-view
stp tc-protection enable
stp tc-protection threshold
number
97
Remarks
—
Required
Use either command.
Required
Disabled by default.
Remarks
—
Optional
Enabled by default.
Optional
6 by default.