A.aggregation congestion occurring at the core layer where the different distribution layer devices feed traffic to the core-layer switches
B.speed mismatches when moving from a low-speed LAN environment to a higher speed WAN environment
C.flapping Ethernet interfaces caused by misconfigured LAN interfaces
D.flapping serial interfaces caused by misconfigured WAN interfaces
E.speed mismatches when moving from a high-speed LAN environment to a lower speed WAN environment