6.5.1

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
specied, regardless of how many management networks have been dened. Use the
das.isolationaddress[...] advanced option to add isolation addresses for additional networks. See
“vSphere HA Advanced Options,” on page 35.
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 rst 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 congure a NIC team for the
management network, congure the vNICs in vSwitch conguration for Active or Standby conguration.
The recommended parameter seings for the vNICs are:
n
Default load balancing = route based on originating port ID
n
Failback = No
After you have added a NIC to a host in your vSphere HA cluster, you must recongure vSphere HA on
that host.
In most implementations, NIC teaming provides sucient heartbeat redundancy, but as an alternative you
can create a second management network connection aached to a separate virtual switch. Redundant
management networking allows the reliable detection of failures and prevents isolation or partition
conditions from occurring, because heartbeats can be sent over multiple networks. The original management
network connection is used for network and management purposes. When the second management network
connection is created, vSphere HA sends heartbeats over both management network connections. If one
path fails, vSphere HA still sends and receives heartbeats over the other path.
N Congure the fewest possible number of hardware segments between the servers in a cluster. The
goal being to limit single points of failure. Also, routes with too many hops can cause networking packet
delays for heartbeats, and increase the possible points of failure.
Using IPv6 Network Configurations
Only one IPv6 address can be assigned to a given network interface used by your vSphere HA cluster.
Assigning multiple IP addresses increases the number of heartbeat messages sent by the cluster's master
host with no corresponding benet.
Chapter 2 Creating and Using vSphere HA Clusters
VMware, Inc. 39