Managing HP Serviceguard A.12.00.00 for Linux, June 2014

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:
• A maximum of 30 network interfaces per node is supported. The interfaces can be physical
NIC ports, VLAN interfaces, Channel Bonds, or any combination of these.
• Only port-based and IP-subnet-based VLANs are supported. Protocol-based VLAN is not
supported because Serviceguard does not support any transport protocols other than TCP/IP.
• Each VLAN interface must be assigned an IP address in a unique subnet.
• Using VLAN in a Wide Area Network cluster is not supported.
3.5.11.4 Additional Heartbeat Requirements
VLAN technology allows great flexibility in network configuration. To maintain Serviceguard’s
reliability and availability in such an environment, the heartbeat rules are tightened as follows
when the cluster is using VLANs:
68 Understanding Serviceguard Software Components