Managing HP Serviceguard for Linux, Sixth Edition, August 2006

Understanding Serviceguard Software Components
How the Network Manager Works
Chapter 368
How the Network Manager Works
The purpose of the network manager is to detect and recover from
network card and cable failures so that network services remain highly
available to clients. In practice, this means assigning IP addresses for
each package to the primary LAN interface card on the node where the
package is running and monitoring the health of all interfaces.
Stationary and Relocatable IP Addresses
Each node (host system) should have an IP address for each active
network interface. This address, known as a stationary IP address, is
configured in the file
/etc/sysconfig/network-scripts/ifcfg-<interface> on Red Hat or
/etc/sysconfig/network/ifcfg-<mac_address> on SUSE. The
stationary IP address is
not associated with packages, and it is not
transferable to another node. Stationary IP addresses are used to
transmit heartbeat messages (described earlier in the section “How the
Cluster Manager Works”) and other data.
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 by the cmmodnet command in the
package control script 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.
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.