Managing HP Serviceguard for Linux, Eighth Edition, March 2008

Understanding Serviceguard Software Components
How the Network Manager Works
Chapter 3 75
IMPORTANT Any subnet identified as a monitored_subnet in the package
configuration file must be configured as a STATIONARY_IP or
HEARTBEAT_IP in the cluster configuration file. See “Cluster
Configuration Parameters” on page 110 and “Package Parameter
Explanations” on page 209.
In addition to the stationary IP address, you normally assign one or more
unique IP addresses to each package. The package IP address is assigned
to the primary LAN interface card when the package starts up.
The IP addresses associated with a package are called relocatable IP
addresses (also known as IP aliases, package IP addresses or
floating IP addresses) because the addresses can actually move from
one cluster node to another. You can use up to 200 relocatable IP
addresses in a cluster spread over as many as 150 packages. This can be
a combination of IPv4 and IPv6 addresses.
Because system multi-node and multi-node packages do not fail over,
they do not have relocatable IP address.
A relocatable IP address is like a virtual host IP address that is assigned
to a package. It is recommended that you configure names for each
package through DNS (Domain Name System). A program then can use
the package’s name like a host name as the input to gethostbyname(3),
which will return the package’s relocatable IP address.
Relocatable addresses (but not stationary addresses) can be taken over
by an adoptive node if control of the package is transferred. This means
that applications can access the package via its relocatable address
without knowing which node the package currently resides on.
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 136,
and in particular the subsection “Implications for Application
Deployment” on page 137.