Intergraph WebScale User Manual page 75

WebScale™ User's Guide
G T
LOSSARY OF ERMS
Adapter card
A hardware plug-in board that connects your computer to a local area network. The
WebScale cluster communicates over the LAN connecting the cluster's hosts.
WebScale currently supports FDDI, Ethernet and fast Ethernet adapter cards. This term
is used interchangeably with network interface card (NIC).
Address Resolution Protocol (ARP)
This standard protocol is used by the TCP/IP Protocol to resolve IP addresses into their
associated MAC addresses prior to communication across a local subnet. When
WebScale uses a multicast cluster MAC address, it assists ARP to ensure that the cluster
IP address(es) are resolved into the corresponding multicast cluster MAC address.
Affinity
In the context of using WebScale to support client sessions, affinity refers to the method
used to associate client requests to cluster hosts. When no affinity is specified, all
network requests are load balanced across the cluster without respect to their source;
this maximizes the scaled performance achieved by load balancing. Affinity can be
increased by directing all client requests from the same IP address to the same cluster
host. Affinity can be further increased by directing all client requests from the same
Class C address range to the same cluster host. Increased affinity enhances the cluster's
ability to support client sessions, although it may somewhat reduce scaled performance.
Availability
Availability is a measure of the fault tolerance of a computer system and its
applications. A highly available system runs twenty-four hours a day, seven days a
week. To do this, the system needs to have redundant components so that it can keep
running even after a portion of the system suffers a failure. Clustering two or more
computers together is an inexpensive and effective means for delivering high
availability. When one computer or software application fails, another member of the
cluster takes over the load and ensures that service is not interrupted.
Class C address (TCP/IP)
A Class C address is one of the most popular of the several forms that a TCP/IP address
can take and meets the needs of many Internet sites. This form allows up to 254 hosts
within a subnet; its subnet mask is 255.255.255.0.
WebScale provides optional session support for Class C addresses (in addition to
support for single IP addresses) to accommodate clients that make use of multiple proxy
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