File name: glossary.html![[AIX HP-UX Linux Solaris Windows]](images/dist.gif)
Glossary
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- ACK
- A control bit (acknowledge) occupying no sequence space, which indicates
that the acknowledgment field of this segment specifies the next sequence
number the sender of this segment is expecting to receive, hence acknowledging
receipt of all previous sequence numbers.
- address
- The unique code assigned to each device or workstation connected to a
network. A standard IPv4 address is a 32-bit address field containing two
parts. The first part is the network address, and the second part is the host
number. An IPv6 address is a 128-bit address field that supports a much higher
number of addresses than IPv4, and IPv6 addresses also support additional
features like multicast and anycast addressing.
- advisor
- Advisors collect and analyze feedback from individual servers,
and inform the manager function.
- agent
- In systems management, a user that, for a particular interaction, has
assumed an agent role.
- An entity that represents one or more managed objects by (a) emitting
notifications regarding the objects and (b) handling requests from managers
for management operations to modify or query the objects.
- alias
- An additional name assigned to a server. The alias makes the server independent
of the name of its host machine. The alias must be defined in the domain name
server.
- API
- Application programming interface. The interface (calling conventions)
by which an application program accesses operating system and other services.
An API is defined at source code level and provides a level of abstraction
between the application and the kernel (or other privileged utilities) to
ensure the portability of the code.
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- backup
- In a high availability configuration, this is the partner of the primary
machine. It monitors the status of the primary machine and takes over if necessary.
See also high availability, primary.
- bandwidth
- The difference between the highest and lowest frequencies of a transmission
channel. This is the amount of data that can be sent through a given communication
circuit per second.
- begin range
- In rules-based load balancing, a lower value specified on a rule. The
default for this value depends on the type of rule.
- binary logging
- Allows server information to be stored in binary files, and then be processed
to analyze the server information that is gathered over time.
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- Caching proxy
- A caching proxy server that can help speed up end-user response
time through highly-efficient caching schemes. Flexible PICS filtering helps
network administrators control access to Web-based information at one central
location.
- CGI
- Common Gateway Interface. A standard for the exchange of information between
a Web server and an external program. The external program can be written
in any language supported by the operating system, and performs tasks not
usually done by the server, such as forms processing.
- CGI script
- A CGI program written in a scripting language such as Perl or REXX that
uses the Common Gateway Interface to perform tasks not usually done by the
server, such as forms processing.
- client
- A computer system or process that requests a service of another computer
system or process. For example, a workstation or personal computer requesting
HTML documents from a Lotus® Domino® Go Webserver is a client of that server.
- cluster
- A group of TCP or UDP servers that are used for the same purpose and are
identified by a single hostname. See also cell.
- cluster address
- The address to which clients connect.
- clustered server
- A server that Load Balancer groups with other servers into a single, virtual
server. Load Balancer balances TCP or UDP traffic among these clustered servers.
- consultant
- Collects server metrics from the servers that are being load balanced
and sends server weight information to the switch that performs the load balancing.
- controller
- A collection of one or more consultants.
- cross port affinity
- Cross port affinity is the affinity (sticky) feature expanded
to cover across multiple ports. See also sticky time.
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- daemon
- Disk And Execution Monitor. A program that is not involved explicitly,
but lies dormant waiting for some condition(s) to occur. The idea is that
the perpetrator of the condition need not be aware that a daemon is lurking
(though often a program will commit an action only because it knows that it
will implicitly invoke a daemon).
- default
- A value, attribute, or option that is assumed when none is explicitly
specified.
- destination address
- The address of the high availability partner machine to which heartbeats
and responses are sent.
- Dispatcher
- A component of Load Balancer that efficiently balances TCP or
UDP traffic among groups of individual linked servers. The Dispatcher machine
is the server running the Dispatcher code.
- domain name server
- DNS. A general-purpose distributed, replicated, data query service chiefly
used on Internet for translating hostnames into Internet addresses. Also,
the style of hostname used on the Internet, though such a name is properly
called a fully qualified domain name. DNS can be configured to use a sequence
of name servers, based on the domains in the name being looked for, until
a match is found.
- dotted-decimal notation
- The syntactical representation for a 32-bit integer that consists of four
8-bit numbers, written in base 10 and separated by periods (dots). It is used
to represent IPv4 addresses.
- dscontrol
- Provides the interface to the Dispatcher component of Load Balancer.
- dsserver
- Handles the requests from the command line to the executor, manager, and
advisors.
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- end range
- In rules-based load balancing, a higher value specified on a rule. The
default for this value depends on the type of rule.
- Ethernet
- A standard type of local area network (LAN). It allows multiple stations
to access the transmission medium at will without prior coordination, avoids
contention by using carrier sense and deference, and resolves contention by
using collision detection and transmission. Software protocols used by Ethernet
systems vary, but include TCP/IP.
- executor
- One of several functions. The executor routes requests to the
TCP or UDP servers, and also monitors the number of new, active, and finished
connections and does garbage collection of completed or reset connections.
The executor supplies the new and active connections to the manager function.
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- FIN
- A control bit (finis) occupying one sequence number, which indicates that
the sender will send no more data or control occupying sequence space.
- FIN state
- The status of a transaction that has finished. When a transaction is in
FIN state, the garbage collector can clear the memory reserved for the connection.
- Firewall
- A computer that connects a private network, such as a business, to a public
network, such as the Internet. It contains programs that limit the access
between two networks. See also proxy gateway.
- FQDN
- Fully Qualified Domain Name. The full name of a system, consisting of
its local hostname and its domain name, including a top-level domain (tld).
For example, "venera" is a hostname and "venera.isi.edu" is an FQDN. An FQDN
should be sufficient to determine a unique Internet address for any host on
the Internet. This process, called "name resolution", uses the Domain Name
System (DNS).
- FTP (File Transfer Protocol)
- An application protocol used for transferring files to and from network
computers. FTP requires a user ID and sometimes a password to allow access
to files on a remote host system.
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- gateway
- A functional unit that interconnects two computer networks with different
architectures.
- GRE
- Generic Routing Encapsulation. A protocol which allows an arbitrary network
protocol A to be transmitted over any other arbitrary protocol B, by encapsulating
the packets of A within GRE packets, which in turn are contained within packets
of B.
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- heartbeat
- A simple packet sent between two machines in high availability mode used
by the standby machine to monitor the health of the active machine.
- high availability
- A feature in which one Load Balancer machine can take over the function
of another, if the primary machine is no longer available.
- host
- A computer, connected to a network, that provides an access point to that
network. A host can be a client, a server, or both simultaneously.
- host name
- The symbolic name assigned to a host. Host names are resolved to IP addresses
through a domain name server.
- HTML (Hypertext Markup Language)
- The language that is used to create hypertext documents. Hypertext documents
include links to other documents that contain additional information about
the highlighted term or subject. HTML controls the format of text and position
of form input areas, for example, as well as the navigable links.
- HTTP (Hypertext Transfer Protocol)
- The protocol used to transfer and display hypertext documents.
- HTTPS (Hypertext Transfer Protocol, Secure)
- The protocol used to transfer and display hypertext documents using SSL.
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- ICMP
- Internet Control Message Protocol. A message control and error-reporting
protocol between a host server and a gateway to the Internet.
- IMAP
- Internet Message Access Protocol. A protocol allowing a client
to access and manipulate electronic mail messages on a server. It permits
manipulation of remote message folders (mailboxes), in a way that is functionally
equivalent to local mailboxes.
- Internet
- The worldwide collection of interconnected networks that use the Internet
suite of protocols and permit public access.
- intranet
- A secure, private network that integrates Internet standards and applications
(such as Web browsers) with an organization's existing computer networking
infrastructure.
- IP
- Internet Protocol. A connectionless protocol that routes data through
a network or interconnected networks. IP acts as an intermediary between the
higher protocol layers and the physical layer.
- IP address
- Internet Protocol address. The unique address that specifies the actual
location of each device or workstation in a network. It is also known as an
Internet address.
- IPSEC
- Internet Protocol Security. A developing standard for security
at the network or packet processing layer of network communication.
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- LAN
- Local Area Network. A computer network of devices connected within
a limited geographical area for communication and which can be connected to
a larger network.
- loopback alias
- An alternative IP address associated with the loopback interface.
The alternative address has the useful side affect of not advertising on a
real interface.
- loopback interface
- An interface that bypasses unnecessary communications functions when the
information is addressed to an entity within the same system.
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- MAC address
- Media Access Control address. The hardware address of a device
connected to a shared network medium.
- managed node
- In Internet communications, a workstation, server, or router that contains
a network management agent. In the Internet Protocol (IP), the managed node
usually contains a Simple Network Management Protocol (SNMP) agent.
- manager
- Sets weights of servers based on internal counters in the executor
and feedback that is provided by the advisors. The executor then uses the
weights to perform load balancing.
- mark down
- To break all active connections to a server and stop any new connections
or packets from being sent to that server.
- mark up
- To allow a server to receive new connections.
- metric
- A process or command that returns a numeric value that can be
used in load balancing on the network, for example, the number of users currently
logged on.
- metric address
- The address where the metric server connects.
- metric collector
- Resides in the consultant and is responsible for collecting a metric or
metrics.
- Metric Server
- Formerly known as Server Monitor Agent (SMA). Metric server provides
system specific metrics to the manager.
- MIB
- Management Information Base. A collection of objects that can be accessed
by means of a network management protocol.
- A definition for management information that specifies the information
available from a host or gateway and the operations allowed.
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- netmask
- For IPv4, a 32–bit mask used to identify the subnetwork address bits in
the host portion of an IP address.
- network
- Hardware and software data communication system. Networks are often classified
according to their geographical extent, local area network (LAN), metropolitan
area network (MAN), wide area network (WAN) and also according to the protocols
used.
- Network Address Translation
- NAT, or Network Address Translator, Virtual LAN. A hardware device currently
being developed and used to extend the Internet addresses already in use.
It allows duplicate IP addresses to be used within a corporation and unique
addresses outside.
- Network Address Port Translation
- NAPT, also known as port mapping. This allows you to configure multiple
server daemons within one physical server to listen on different port numbers.
- network management station
- In the Simple Network Management Protocol (SNMP), a station that runs
management application programs that monitor and control network elements.
- network proximity
- The proximity of two networked entities, such as a client and server,
which determines by measuring round-trip time.
- NFA (nonforwarding address)
- The primary IP address of the machine, used for administration and configuration.
- NIC
- Network Interface Card. An adapter circuit board installed in a computer
to provide a physical connection to a network.
- NNTP
- Network News Transfer Protocol. A TCP/IP protocol for transferring news
items.
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- packet
- The unit of data that is routed between an origin and a destination
on the Internet or any other packet-switched network.
- PICS
- Platform for Internet Content Selection. PICS-enabled clients
allow the users to determine which rating services they want to use and, for
each rating service, which ratings are acceptable and which are unacceptable.
- ping
- A command that sends Internet Control Message Protocol (ICMP) echo-request
packets to a host, gateway, or router with the expectation of receiving a
reply.
- POP3
- Post Office Protocol 3. A protocol used for exchanging network mail and
accessing mailboxes.
- port
- A number that identifies an abstracted communication device. Web servers
use port 80 by default.
- primary
- In a high availability configuration, the machine that starts out as the
machine actively routing packets. Its partner, the backup machine, monitors
the status of the primary machine and takes over if necessary. See also backup,
high availability.
- priority
- In rules-based load balancing, the level of importance placed upon any
given rule. The evaluates rules from the first priority level to the last
priority level.
- private network
- A separate network on which Load Balancer communicates with clustered
servers for performance reasons.
- protocol
- The set of rules governing the operation of functional units of a communication
system if communication is to take place. Protocols can determine low-level
details of machine-to-machine interfaces, such as the order in which bits
from a byte are sent; they can also determine high-level exchanges between
application programs, such as file transfer.
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- Quality of Service (QoS)
- The performance properties of a network service, including throughput,
transit delay and priority. Some protocols allow packets or streams to include
QoS requirements.
- quiesce
- To end a process by allowing operations to complete normally.
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- reach
- An advisor that issues pings to a given target and reports whether that
target is responding.
- reach address
- In a high availability configuration, the address of the target to which
the advisor should issue pings to see if the target is responding.
- return address
- A unique IP address or hostname. It is configured on the Load Balancer
machine and used as its source address when load balancing the client's request
to the server.
- RMI
- Remote Method Invocation. Part of the Java programming language library which
enables a Java program running on one computer to access the objects
and methods of another Java program running on a different computer.
- root user
- The unrestricted authority to access and modify any part of the AIX®,
Red Hat Linux,
or Solaris operating system, usually associated with the user who manages
the system.
- route
- The path of network traffic from origin to destination.
- router
- A device which forwards packets between networks. The forwarding decision
is based on network layer information and routing tables, often constructed
by routing products.
- RPM
- Red Hat Package Manager.
- rule
- In rules-based load balancing, a mechanism for grouping servers such that
a server can be chosen based on information other than the destination address
and port.
- rule type
- In rules-based load balancing, an indicator of the information that should
be evaluated to determine whether a rule is true.
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- scalable
- Pertaining to the capability of a system to adapt readily to a greater
or lesser intensity of use, volume, or demand. For example, a scalable system
can efficiently adapt to work with larger or smaller networks performing tasks
of varying complexity.
- server
- A computer that provides shared services to other computers over a network;
for example, a file server, a print server, or a mail server.
- server address
- The unique code assigned to each computer that provides shared services
to other computers over a network; for example, a file server, a print server,
or a mail server. The server address can be either the IP address or the
host name.
- server machine
- A server that Load Balancer groups with other servers into a single, virtual
server. Load Balancer balances traffic among the server machines. Synonymous
with clustered server.
- service
- A function provided by one or more nodes; for example, HTTP, FTP, Telnet.
- shell
- The software that accepts and processes command lines from a
user's workstation. The bash shell is one of several UNIX® shells available.
- site name
- A site name is an unresolvable host name that the client will request.
For example, a web site has 3 servers (1.2.3.4, 1.2.3.5, and 1.2.3.6) configured
for site name www.dnsload.com. When a client requests this site name,
one of the three server IP addresses will be returned as the resolution. The
site name must be a fully qualified domain name, for example: dnsload.com.
An unqualified name, for example, dnsload is invalid for a site name.
- Site Selector
- A DNS-based load balancing component of . Site Selector balances
the load on servers within a wide area network (WAN) using measurements and
weights that are gathered from the Metric Server component running on those
servers.
- SMTP
- Simple Mail Transfer Protocol. In the Internet suite of protocols, an
application protocol for transferring mail among users in the Internet environment.
SMTP specifies the mail exchange sequences and message format. It assumes
that the Transmission Control Protocol (TCP) is the underlying protocol.
- SNMP
- Simple Network Management Protocol. The Internet standard protocol, defined
in STD 15, RFC 1157, developed to manage nodes on an IP network. SNMP is
not limited to TCP/IP. It can be used to manage and monitor all sorts of equipment
including computers, routers, wiring hubs, toasters and jukeboxes.
- source address
- In a high availability configuration, the address of the high availability
partner machine that sends heartbeats.
- SPARC
- Scalable processor architecture.
- sscontrol
- Provides the interface to the Site Selector component of .
- SSL
- Secure Sockets Layer. A popular security scheme developed by Netscape
Communications Corp. along with RSA Data Security Inc. SSL allows the client
to authenticate the server and all data and requests to be encrypted. The
URL of a secure server protected by SSL begins with https (rather than HTTP).
- sticky time
- The interval between the closing of one connection and the opening of
a new connection during which a client will be sent back to the same server
used during the first connection. After the sticky time, the client may be
sent to a server different from the first.
- strategy
- In a high availability configuration, a keyword for specifying how recovery
takes place following the failure of the active machine.
- subnet mask
- For IPv4, a 32–bit mask used to identify the subnetwork address bits in
the host portion of an IP address.
- SYN
- A control bit in the incoming segment, occupying one sequence number,
used at the initiation of a connection, to indicate where the sequence numbering
will start.
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- TCP
- Transmission Control Protocol. A communications protocol used on the Internet.
TCP provides reliable host-to-host exchange of information. It uses IP as
the underlying protocol.
- TCP/IP
- Transmission Control Protocol/Internet Protocol. A suite of protocols
designed to allow communication between networks regardless of the communication
technologies used in each network.
- TCP server machine
- A server that links with other servers into a single, virtual server.
balances TCP traffic among the TCP server machines. Synonymous with clustered
server.
- Telnet
- Terminal emulation protocol, a TCP/IP application protocol for remote
connection service. Telnet allows a user at one site to gain access to a remote
host as if the user’s workstation were connected directly to that remote host.
- timeout
- The time interval allotted for an operation to occur.
- TOS
- Type of service. A one byte field in the IP header of the SYN
packet.
- TTL
- A DNS TTL (time to live) is the number of seconds a client can cache the
name resolution response.
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- UDP
- User Datagram Protocol. In the Internet suite of protocols, a protocol
that provides unreliable, connectionless datagram service. It enables an application
program on one machine or process to send a datagram to an application program
on another machine or process. UDP uses the Internet Protocol (IP) to deliver
datagrams.
- URI
- Universal Resource Identifier. The encoded address for any resource on
the Web, such as HTML document, image, video clip, program, and so forth.
- URL
- Uniform Resource Locator. A standard way of specifying the location of
an object, typically a web page, on the Internet. URLs are the form of address
used on the World-Wide Web. They are used in HTML documents to specify the
target of a hyperlink which is often another HTML document (possibly stored
on another computer).
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- VPN
- Virtual Private Network (VPN). A network comprised of one or
more secure IP tunnels connecting two or more networks.
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- WAN
- Wide Area Network. A network that provides communication services to a
geographic area larger than that served by a local area network or a metropolitan
area network, and that may use or provide public communication facilities.
- WAP
- Wireless Application Protocol. This is an open international standard
for applications that use wireless communication. For example, this standard
includes internet access from a mobile phone.
- WAS
- WebSphere® Application
Server.
- Web
- The network of HTTP servers that contain programs and files, many of them
hypertext documents that contain links to other documents on HTTP servers.
Also World Wide Web.
- wizard
- A dialog within an application that uses step-by-step instructions
to guide a user through a specific task.
- WLM
- Workload Manager. An advisor that is provided with Load Balancer.
It is designed to work only in conjunction with servers on OS/390® mainframes
running the MVS Workload
Manager (WLM) component.
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