Managing HP Serviceguard A.11.20.20 for Linux, March 2014

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” (page 130), and in particular the subsection“Implications for
Application Deployment” (page 131).
When a package switch occurs, 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 (specified as monitored_subnets in the package configuration file), all those
subnets must normally be available on the target node before the package will be started. (In a
cross-subnet configuration, all subnets configured on 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 .
3.5.10 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.
3.5.11 VLAN Configurations
Virtual LAN configuration (VLAN) is supported in Serviceguard clusters.
3.5.11.1 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.
3.5.11.2 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.
3.5.11.3 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 cluster node. To prevent this and
other problems, Serviceguard imposes the following restrictions:
70 Understanding Serviceguard Software Components