Load Balancer Glossary
A
- 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 IP address is a 32-bit address field.
This field contains two parts. The first part is the network address;
the second part is the host number.
- advisor
- The advisors are a function of the Load Balancer components. Advisors
collect and analyze feedback from individual servers and inform the manager
component.
- agent
- (1) In systems management, a user that, for a particular interaction, has
assumed an agent role.
- (2) 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.
B
- backup
- In high availability for the Dispatcher, 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; 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.
C
- 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.
- CBR (Content Based Routing)
- A component of Load Balancer. CBR works with Caching Proxy to load balance incoming
client requests, based on Web page content using specified rule types, to HTTP or HTTPS servers.
- cbrcontrol
- Provides the interface to the Content Based Routing component of Load Balancer.
- cbrserver
- In Content Based Routing, handles the requests from the command line to the executor, manager and
advisors.
- ccocontrol
- In Cisco CSS Controller, provides the interface to the Cisco CSS switch.
- ccoserver
- In Cisco CSS Controller, handles the requests from the command line to the consultants.
- 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.
- Cisco CSS Controller (CCO)
- A component of Load Balancer. Cisco CSS Controller uses Load Balancer technology
to provide real-time load balancing information to the Cisco Content Services Switch.
- Cisco CSS Switch
- Any of Cisco's CSS 11000 series switches, used for packet
forwarding and content routing.
- 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
- The cluster name or address to which clients connect. The cluster value is either a
symbolic name or in dotted-decimal format. A cluster value of 0.0.0.0 can be used to
specify a wildcard cluster.
- Cluster Address
- The address to which clients connect. The cluster address can be either the
dotted-decimal IP address or the host name of the machine. If the cluster value is not resolvable,
you must provide this IP address of the physical machine.
- clustered server
- A server that the Dispatcher groups with other servers into a single,
virtual server. Load Balancer balances TCP or UDP traffic among
these clustered servers.
- collocate
- When Load Balancer is
installed on the same machine it is load balancing. Collocate only applies
to AIX, Red Hat Linux, SuSE Linux and Solaris operating systems.
- consultant
- Collects server metrics from the servers (which 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
- The affinity (sticky) feature expanded to cover across multiple ports.
D
- 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. Dispatcher, CBR,
Site Selector, Cisco CSS Controller and Nortel Alteon Controller are all called components of
Load Balancer. Each of these components have functions.
- DNS (Domain Name Server)
- 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 IP addresses.
- dscontrol
- Provides the interface to the Dispatcher component of Load Balancer.
- dsserver
- In Dispatcher, handles the requests from the command line to the executor, manager, and advisors.
E
- 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 Load Balancer 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 component. For Cisco CSS Controller or Nortel Alteon Controller, the executor holds the
configuration information and contains the information required
to connect to the Cisco CSS Switch or the Nortel Alteon Switch.
F
- 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. Once a transaction
is in FIN state, the Load Balancer 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.
G
- 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.
H
- heartbeat
- A simple packet sent between two Load Balancer machines in high availability
mode used by the standby Load Balancer to monitor the health of the active
Dispatcher.
- high availability
- A Load Balancer feature in which one Load Balancer can take over the function of
another, should that part fail.
- 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 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
I
- Internet
- The worldwide collection of interconnected networks that use the Internet
suite of protocols and permit public access.
- 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.
- 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 32-bit 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.
L
- 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 effect 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.
M
- 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
- One of several Load Balancer functions existing on all components. The manager sets weights based
on internal counters in the executor and feedback 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(s) of Load Balancer components.
- MIB
- (1) Management Information Base. A collection of objects that can be
accessed by means of a network management protocol.
- (2) A definition for management information that specifies the information
available from a host or gateway and the operations allowed.
- multiple address collocation
- Multiple address collocation allows the customer to specify the address of the
collocated server to be different than the nonforwarding address (NFA) in the
configuration.
- mutual high availability
- Mutual high availability allows two Dispatcher machines to be both primary and backup for each other.
N
- nalcontrol
- Provides the interface to the Nortel Alteon Controller component of Load Balancer.
- nalserver
- In Nortel Alteon Controller, a script that starts the Nortel Alteon Controller in a java virtual
machine.
- netmask
- For Internet subnetworking, 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)
- Allows you to configure multiple server daemons within one physical server to respond to
requests to different IP addresses
- 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 executes
management application programs that monitor and control network
elements.
- network proximity
- The proximity of two networked entities, such as a client and server, which Site Selector determines by
measuring round-trip time.
- 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.
- nonforwarding address (nfa)
- The primary IP address of the Load Balancer machine, used for administration and
configuration.
- Nortel Alteon Controller
- A component of IBM Load Balancer. Nortel Alteon Controller uses Load Balancer technology to provide real-time
load balancing information to the Nortel Alteon Web Switch.
- Nortel Alteon Web Switch
- The Nortel Alteon ACE Director Series Switch and the Nortel Alteon 180 Series Switch from
the Alteon Web Switching portfolio, used for packet forwarding and content routing.
P
- 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 high availability for the Dispatcher, 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 Dispatcher 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.
Q
- 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.
R
- reach
- In Dispatcher, an advisor that issues pings to a given target and reports
whether that target is responding.
- reach address
- In high availability for the Dispatcher, 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 Dispatcher machine and used by Dispatcher
as its source address when load balancing the client's request to the server.
- RMI (Remote Method Invocation)
- A method used by a programmer, using the Java programming language and development
environment, to write object-oriented programs in which objects on different computers
can interact in a distributed network.
- root user
- The unrestricted authority to access and modify any part of the AIX, Red
Hat Linux, SUSE 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.
S
- 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. A standard IP address is a 32-bit address field.
The server address can be either the dotted decimal IP address or the host
name.
- server machine
- A server that the Dispatcher groups with other servers into a single,
virtual server. The Dispatcher balances traffic among the server
machines. Synonymous with clustered server.
- service
- A function provided by one or more nodes; for example, HTTP, FTP,
Telnet.
- For Nortel Alteon Controller, a service is the function or information requested by an end
user from a site. It is identified by a virtual IP address and a virtual port number by an end user
request. On the switch, it is defined by a virtual server identifier, which is an integer
and a virtual port number or service name.
- For Cisco CSS Controller, a service is a destination location where a piece of content physically
resides. For example, a local or remote server and port.
- 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 (aka host 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, on 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 component of Load Balancer. Site Selector works in conjunction with a name server to load
balance among a group of servers 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 high availability for the Dispatcher, 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 Load Balancer.
- 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).
- ssserver
- In Site Selector, handles the requests from the command line to the nameserver, manager and
advisors.
- 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 high availability for the Dispatcher, a keyword for specifying how
recovery takes place following the failure of the active machine.
- subnet mask
- For Internet subnetworking, 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.
T
- 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 Load Balancer links with other servers into a single,
virtual server. Load Balancer 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.
- Time to Live (TTL)
- A DNS TTL is the number of seconds a client can cache the name resolution response.
- timeout
- A period of time after which an error is raised if some event has not occurred. A common example
is sending a message. If the receiver does not acknowledge the message with some preset timeout
period, a transmission error is assumed to have occurred.
- TOS (Type of Service)
- A one byte field in the IP header of the SYN packet.
U
- 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).
V
- VPN (Virtual Private Network)
- A network comprised of one or more
secure IP tunnels connecting two or more networks.
W
- 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 are network, and that may use or provide public communication facilities.
- WAP (Wireless Application Protocol)
- An open international standard for applications that use wireless communication, e.g.
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 provided with Dispatcher. 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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