HP Serviceguard A.11.20- Managing Serviceguard Twentieth Edition, August 2011

A package switch normally involves moving a failover package and its associated IP addresses
to a new system on the same subnet. In this case, the new system must have the same subnet
configured and working properly; otherwise the package 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 known as 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 IP address for each subnet the package is configured to
start on; see “About Cross-Subnet Failover” (page 154), and in particular the subsection “Implications
for Application Deployment” (page 155).
When a package fails over, 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, normally all of them must be available on the target node before the package will be
started. (In a cross-subnet configuration, all the monitored subnets that are specified for this package,
and configured on the target node, must be up.)
If the package has a dependency on a resource or another package, the dependency must be met
on the target node before the package can start.
The switching of relocatable IP addresses on a single subnet is shown in Figure 14 and Figure 15.
Figure 14 shows a two node cluster in its original state with Package 1 running on Node 1 and
Package 2 running on Node 2. Users connect to the node with the IP address of the package they
wish to use. Each node has a stationary IP address associated with it, and each package has an
IP address associated with it.
Figure 14 Before Package Switching
Figure 15 shows the condition where Node 1 has failed and Package 1 has been transferred to
Node 2 on the same subnet. Package 1’s IP address was transferred to Node 2 along with the
package. Package 1 continues to be available and is now running on Node 2. Also note that
Node 2 can now access both Package1’s disk and Package2’s disk.
52 Understanding Serviceguard Software Components