Managing HP Serviceguard for Linux, Seventh Edition, July 2007

Understanding Serviceguard Software Components
How the Network Manager Works
Chapter 372
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. 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.
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.
Adding and Deleting Relocatable IP Addresses
When a package is started, a relocatable IP address can be added to a
specified IP subnet. When the package is stopped, the relocatable IP
address is deleted from the specified subnet. Adding and removing of
relocatable IP addresses is handled through the cmmodnet command in
the package control script, which is described in detail in the chapter
“Configuring Packages and their Services.”
IP addresses are configured only on each primary network interface
card. Multiple IP addresses on the same network card must belong to the
same IP subnet.
Load Sharing
Serviceguard allows you to configure several services into a single
package, sharing a single IP address; in that case all those services will
fail over when the package does. If you want to be able to load-balance
services (that is, move a specific service to a less loaded system when
necessary) you can do so by putting each service in its own package and
giving it a unique IP address.