6.5.1

Table Of Contents
Network Failure Detection Policy
You can specify one of the following methods that a virtual switch uses for failover detection.
Link status only
Relies only on the link status that the network adapter provides. Detects
failures, such as removed cables and physical switch power failures.
However, link status does not detect the following configuration errors:
n
Physical switch port that is blocked by spanning tree or is
misconfigured to the wrong VLAN .
n
Pulled cable that connects a physical switch to another networking
devices, for example, an upstream switch .
Beacon probing
Sends out and listens for Ethernet broadcast frames, or beacon probes,
that physical NICs send to detect link failure in all physical NICs in a team.
ESXi hosts send beacon packets every second. Beacon probing is most
useful to detect failures in the closest physical switch to the ESXi host,
where the failure does not cause a link-down event for the host.
Use beacon probing with three or more NICs in a team because ESXi can
detect failures of a single adapter. If only two NICs are assigned and one of
them loses connectivity, the switch cannot determine which NIC needs to
be taken out of service because both do not receive beacons and as a
result all packets sent to both uplinks. Using at least three NICs in such a
team allows for n-2 failures where n is the number of NICs in the team
before reaching an ambiguous situation.
Failback Policy
By default, a failback policy is enabled on a NIC team. If a failed physical NIC returns online, the virtual
switch sets the NIC back to active by replacing the standby NIC that took over its slot.
If the physical NIC that stands first in the failover order experiences intermittent failures, the failback
policy might lead to frequent changes in the NIC that is used. The physical switch sees frequent changes
in MAC addresses, and the physical switch port might not accept traffic immediately when an adapter
becomes online. To minimize such delays, you might consider changing the following settings on the
physical switch:
n
Disable Spanning Tree Protocol (STP) on physical NICs that are connected to ESXi hosts .
n
For Cisco based networks, enable PortFast mode for access interfaces or PortfFast trunk mode for
trunk interfaces. This might save about 30 seconds during the initialization of the physical switch port.
n
Disable the trunking negotiation.
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