R3721-F3210-F3171-HP High-End Firewalls Network Management Configuration Guide-6PW101

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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 may 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.
To enable loop guard:
Ste
p
Command Remarks
1. Enter system view.
system-view N/A
2. Enter Ethernet interface view or Layer 2
aggregate interface view.
interface interface-type
interface-number
N/A
3. Enable the loop guard function for the ports. stp loop-protection Disabled by default.
NOTE:
• Do not enable loop guard on a port connecting user terminals. Otherwise, the port will stay in the
discarding state in all MSTIs because it cannot receive BPDUs.
• Among loop guard, root guard and edge port settings, only one function (whichever is confi
g
ured the
earliest) can take effect on a port at the same time.
Enabling TC-BPDU guard
When a device receives topology change (TC) BPDUs (the BPDUs that notify devices of topology
changes), it flushes the forwarding address entries. If someone forges TC-BPDUs to attack the device, the
device 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 certain 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.
To enable TC-BPDU guard:
Ste
p
Command Remarks
1. Enter system view.
system-view N/A
2. Enable the TC-BPDU guard function.
stp tc-protection enable
Optional.
Enabled by default.
3. Configure the maximum number of
forwarding address entry flushes that the
device can perform every 10 seconds.
stp tc-protection threshold
number
Optional.
6 by default.