When a physical NIC experiences frequent link status flapping, ESXi may turn off the physical NIC to avoid unnecessary link failover and network instability.
For example, a physical NIC driver may reset the physical NIC when it detects "tx Hang". A reset causes a link down/up event to be generated. If the physical NIC is itself bad, this causes periodic reset and link status flapping. The
vmkernel.log log file on the ESXi host will show that one or more network cards and constantly changing from a Down to Up state and visa versa.
During link status flapping, traffic may migrate between different physical NICs. If the flapping is too frequent, you experience network issues, such as bandwidth reduction or an unstable network.