Managing HP Serviceguard for Linux, Tenth Edition, September 2012

that node, and identified as monitored subnets in the package configuration file, must
be available.)
The switching of relocatable IP addresses is shown in Figure 11 and Figure 12 .
Address Resolution Messages after Switching on the Same Subnet
When a relocatable IP 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 IP address that has been moved. All
systems receiving the broadcast should update the associated ARP cache entry to reflect
the change. Currently, the ARP messages are sent at the time the IP address is added to
the new system. An ARP message is sent in the form of an ARP request. The sender and
receiver protocol address fields of the ARP request message are both set to the same
relocatable IP address. This ensures that nodes receiving the message will not send
replies.
Unlike IPv4, IPv6 addresses use NDP messages to determine the link-layer addresses of
their neighbors.
VLAN Configurations
Virtual LAN configuration (VLAN) is supported in Serviceguard clusters.
What is VLAN?
VLAN is a technology that allows logical grouping of network nodes, regardless of their
physical locations.
VLAN can be used to divide a physical LAN into multiple logical LAN segments or
broadcast domains, helping to reduce broadcast traffic, increase network performance
and security, and improve manageability.
Multiple VLAN interfaces, each with its own IP address, can be configured from a physical
LAN interface; these VLAN interfaces appear to applications as ordinary network
interfaces (NICs). See the documentation for your Linux distribution for more information
on configuring VLAN interfaces.
Support for Linux VLAN
VLAN interfaces can be used as heartbeat as well as data networks in the cluster. The
Network Manager monitors the health of VLAN interfaces configured in the cluster, and
performs remote failover of VLAN interfaces when failure is detected. Failure of a VLAN
interface is typically the result of the failure of the underlying physical NIC port or Channel
Bond interface.
Configuration Restrictions
Linux allows up to 1024 VLANs to be created from a physical NIC port. A large pool
of system resources is required to accommodate such a configuration; Serviceguard
could suffer performance degradation if many network interfaces are configured in each
80 Understanding Serviceguard Software Components