Managing Serviceguard Fifteenth Edition, reprinted May 2008

Understanding Serviceguard Software Components
How the Network Manager Works
Chapter 3 107
Remote Switching
A remote switch (that is, a package switch) involves moving packages to
a new system. In the most common configuration, in which all nodes are
on the same subnet(s), the package IP (relocatable IP; see “Stationary
and Relocatable IP Addresses” on page 99) moves as well, and the new
system must already have the subnet configured and working properly,
otherwise the packages will not be started.
NOTE It is possible to configure a cluster that spans subnets joined by a router,
with some nodes using one subnet and some another. This is called a
cross-subnet configuration. In this context, you can configure packages
to fail over from a node on one subnet to a node on another, and you will
need to configure a relocatable address for each subnet the package is
configured to start on; see “About Cross-Subnet Failover” on page 191,
and in particular the subsection “Implications for Application
Deployment” on page 192.
When a remote switch occurs, TCP connections are lost. TCP
applications must reconnect to regain connectivity; this is not handled
automatically. Note that if the package is dependent on multiple subnets
(specified as monitored_subnets in the package configuration file), all
those subnets must normally be available on the target node before the
package will be started. (In a cross-subnet configuration, all subnets
configured on that node, and identified as monitored subnets in the
package configuration file, must be available.)
Note that remote switching is supported only between LANs of the same
type. For example, a remote switchover between an Ethernet interface on
one machine and an IPoIB interface on the failover machine is not
supported. The remote switching of relocatable IP addresses is shown in
Figure 3-5 and Figure 3-6.
Address Resolution Messages after Switching on the Same
Subnet
When a floating IPv4 address is moved to a new interface, either locally
or remotely, an ARP message is broadcast to indicate the new mapping
between IP address and link layer address. An ARP message is sent for
each IPv4 address that has been moved. All systems receiving the
broadcast should update the associated ARP cache entry to reflect the