Abstract: When deploying VPLS service, E-LAN loop will cause broadcast storm, MAC address flapping,
at last it cause service interruption.
Product Line: Carrier IP Product Family: PTN
Product Model: PTN3900&3900-8&PTN1900&PTN960&PTN950&PTN910
Trigger conditions:
When Deploying VPLS services, we must avoid loop, such as PW , UNI interface and external device.
PW logical loop in a single VPLS. When two parallel homologous and homoclinic PWs are added into
VPLS without Split Horizon Group configured, it will certainly cause a loop.
Loop is generated by VPLS and other service or other device.
VPLS UNI loopback. For example, when two UNI connects to each other, or go to the same switch/OLT
ELAN, or port loopback, loop will be generated.
Fault appearance:
When a large amount of broadcast traffic occurs on link of VPLS, causing broadcast storm, link
congestion, or MAC address flapping and finally cause service interruption.
Judgment method:
Where the link of VPLS goes far beyond the usual flow of broadcast packets. In normal situation,
broadcast and multicast traffic are relatively low. When the problem happens, you can see lots
broadcast traffic through the port RMON performance, such as 1MB or more on FE. Checking
method is as the figure below.
Traffic congestion occurs. Alarm like FLOW_OVER, ETH_TX_FLOW_OVER, ETH_RX_FLOW_OVER
ETH etc are reported MAC address flapping appears. PW or UNI learn the wrong MAC address. When
continue query the MAC address self-learning table, it can be found that a MAC address learned from
different interface (PW/UNI) from time to time.
Root Cause:
When loop is generated in VPLS, the broadcast traffic will be numerously copied and cause broadcast
storm. Meanwhile, it will cause MAC address flapping.
Impact and Risk:
Broadcast storm will generate congestion on link and cause other service interruption, MAC address
flapping will affects the service itself
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