6.0.1

Networks Used for vSphere HA Communications
To identify which network operations might disrupt the functioning of vSphere HA, you should know
which management networks are being used for heart beating and other vSphere HA communications.
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On legacy ESX hosts in the cluster, vSphere HA communications travel over all networks that are
designated as service console networks. VMkernel networks are not used by these hosts for vSphere
HA communications. To contain vSphere HA traffic to a subset of the ESX console networks, use the
allowedNetworks advanced option.
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On ESXi hosts in the cluster, vSphere HA communications, by default, travel over VMkernel networks.
With an ESXi host, if you wish to use a network other than the one vCenter Server uses to communicate
with the host for vSphere HA, you must explicitly enable the Management traffic checkbox.
To keep vSphere HA agent traffic on the networks you have specified, configure hosts so vmkNICs used by
vSphere HA do not share subnets with vmkNICs used for other purposes. vSphere HA agents send packets
using any pNIC that is associated with a given subnet if there is also at least one vmkNIC configured for
vSphere HA management traffic. Consequently, to ensure network flow separation, the vmkNICs used by
vSphere HA and by other features must be on different subnets.
Network Isolation Addresses
A network isolation address is an IP address that is pinged to determine whether a host is isolated from the
network. This address is pinged only when a host has stopped receiving heartbeats from all other hosts in
the cluster. If a host can ping its network isolation address, the host is not network isolated, and the other
hosts in the cluster have either failed or are network partitioned. However, if the host cannot ping its
isolation address, it is likely that the host has become isolated from the network and no failover action is
taken.
By default, the network isolation address is the default gateway for the host. Only one default gateway is
specified, regardless of how many management networks have been defined. You should use the
das.isolationaddress[...] advanced option to add isolation addresses for additional networks. See
“vSphere HA Advanced Options,” on page 38.
Network Path Redundancy
Network path redundancy between cluster nodes is important for vSphere HA reliability. A single
management network ends up being a single point of failure and can result in failovers although only the
network has failed. If you have only one management network, any failure between the host and the cluster
can cause an unnecessary (or false) failover activity if heartbeat datastore connectivity is not retained during
the networking failure. Possible failures include NIC failures, network cable failures, network cable
removal, and switch resets. Consider these possible sources of failure between hosts and try to minimize
them, typically by providing network redundancy.
The first way you can implement network redundancy is at the NIC level with NIC teaming. Using a team
of two NICs connected to separate physical switches improves the reliability of a management network.
Because servers connected through two NICs (and through separate switches) have two independent paths
for sending and receiving heartbeats, the cluster is more resilient. To configure a NIC team for the
management network, configure the vNICs in vSwitch configuration for Active or Standby configuration.
The recommended parameter settings for the vNICs are:
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Default load balancing = route based on originating port ID
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Failback = No
After you have added a NIC to a host in your vSphere HA cluster, you must reconfigure vSphere HA on
that host.
Chapter 2 Creating and Using vSphere HA Clusters
VMware, Inc. 41