High CPU Usage on an MSTP Network

Publication Date:  2015-03-24 Views:  205 Downloads:  0
Issue Description
Applicable Products and Versions:S5700 V200R001/V200R002/V200R003

High CPU Usage on an MSTP Network.
Alarm Information
The CPU usage is high on the S5700 on an MSTP network.

Handling Process
1.  Check interface statistics and check whether there is high bandwidth usage on any interface.

<Quidway> display interface brief
…………
Interface                  PHY   Protocol InUti OutUti   inErrors  outErrors
GigabitEthernet4/0/1       up    up       0.72%    81%          0          0
GigabitEthernet4/0/2       up    up         81%  0.73%          2          0


2.  Run the display stp tc-bpdu statistics command to check the number of TC and TCN BPDUs received and sent by each interface. The command output shows that a large number of TC BPDUs are received.

<Quidway> display stp tc-bpdu statistics
-------------------------- STP TC/TCN information --------------------------
MSTID Port                        TC(Send/Receive)      TCN(Send/Receive)
0     GigabitEthernet4/0/1               3/2                   0/0
0     GigabitEthernet1/0/10              14/9                  0/
0


It is difficult to locate the fault that causes topology changes. To resolve the high CPU usage problem, perform the following operations:
  • Run the arp topology-change disable command to disable the switch from deleting aged ARP entries upon network topology changes.
  • Run the mac-address update arp command to enable the switch to update outbound interfaces in ARP entries when outbound interfaces in MAC address entries change.
NOTE:
V100R006 and later versions support the mac-address update arp command. V200R001 and later versions support the arp topology-change disable command.

After the preceding operations are performed, the CPU usage decreases greatly.


Root Cause
When network topology recalculation occurs on an MSTP network, a large number of TC BPDUs will be advertised. The switch will then recalculate the topology, causing a high CPU usage.

Suggestions
When a high CPU usage is detected on a switch on an MSTP network, check whether the switch receives a large number of TC BPDUs. If the switch receives a large number of TC BPDUs, disable the switch from deleting aged ARP entries upon network topology changes, and enable the switch to update outbound interfaces in ARP entries when outbound interfaces in MAC address entries change.

END