Manual Chapter : 3-DNS Administrator Guide version 4.2: Glossary

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3-DNS Controller versions 1.x - 4.x

  • 4.2 PTF-10, 4.2 PTF-09, 4.2 PTF-08, 4.2 PTF-07, 4.2 PTF-06, 4.2 PTF-05, 4.2 PTF-04, 4.2 PTF-03, 4.2 PTF-02, 4.2 PTF-01, 4.2.0
Manual Chapter


3-DNS Distributed Traffic Controller

The 3-DNS Distributed Traffic Controller is a wide area load distribution solution that intelligently allocates Internet and intranet service requests across geographically distributed network servers. The 3-DNS Distributed Traffic Controller is also most often referred to as the 3-DNS.

3-DNS Maintenance menu

The 3-DNS Maintenance menu is a command line utility that you use to configure the 3-DNS.

3-DNS web server

The 3-DNS web server is a standard web server that hosts the Configuration utility on the 3-DNS.

A record

The A record is the ADDRESS resource record that a 3-DNS returns to a local DNS server in response to a name resolution request. The A record contains a variety of information, including one or more IP addresses that resolve to the requested domain name.

access control list (ACL)

An access control list is a list of local DNS server IP addresses that are excluded from path probing or hops queries.

active unit

In a redundant system, an active unit is a 3-DNS that currently load balances name resolution requests. If the active unit in the redundant system fails, the standby unit assumes control and begins to load balance requests.

alternate method

The alternate method specifies the load balancing mode that the 3-DNS uses to pick a virtual server if the preferred method fails. See also fallback method, preferred method.

big3d agent

The big3d agent is a monitoring agent that collects metrics information about server performance and network paths between a data center and a specific local DNS server. The 3-DNS uses the information collected by the big3d agent for dynamic load balancing.

BIND (Berkeley Internet Name Domain)

BIND is the most common implementation of the Domain Name System (DNS). BIND provides a system for matching domain names to IP addresses. For more information, refer to

CDN switching

CDN switching is the functionality of the 3-DNS that allows a user to redirect traffic to a third-party network, or transparently switch traffic to a CDN. The two features of the 3-DNS that make CDN switching possible are geographic redirection and the pool type CDN.

CNAME record

A canonical name (CNAME) record acts as an alias to another domain name. A canonical name and its alias can belong to different zones so the CNAME record must always be entered as a fully qualified domain name. CNAME records are useful for setting up logical names for network services so that they can be easily relocated to different physical hosts.

completion rate

The completion rate is the percentage of packets that a server successfully returns during a given session.

Completion Rate mode

The Completion Rate mode is a dynamic load balancing mode that distributes connections based on which network path drops the fewest packets, or allows the fewest number of packets to time out.

Configuration utility

The Configuration utility is the browser-based application that you use to configure the 3-DNS.

content delivery network (CDN)

A content delivery network (CDN) is an architecture of Web-based network components that helps dramatically reduce the wide-area network latency between a client and the content they wish to access. A CDN includes some or all of the following network components: wide-area traffic managers, Internet service providers, content server clusters, caches, and origin content providers.

data center

A data center is a physical location that houses one or more 3-DNS systems, BIG-IP systems, EDGE-FX Caches, GLOBAL-SITE systems, or host machines.

data center server

A data center server is any server recognized in the 3-DNS configuration. A data center server can be any of the following: a 3-DNS, a BIG-IP, an EDGE-FX Cache, a GLOBAL-SITE, or a host.

domain name

A domain name is a unique name that is associated with one or more IP addresses. Domain names are used in URLs to identify particular Web pages. For example, in the URL, the domain name is

dynamic load balancing modes

Dynamic load balancing modes base the distribution of name resolution requests to virtual servers on live data, such as current server performance and current connection load.

dynamic site content
Dynamic site content is a type of site content that is automatically generated each time a user accesses the site. Examples are current stock quotes or weather satellite images.

Extended Content Verification (ECV)

On the 3-DNS, ECV is a service monitor that checks the availability of actual content, (such as a file or an image) on a server, rather than just checking the availability of a port or service, such as HTTP on port 80.

external interface

An external interface is the network interface that can be accessed across a wide-area network (WAN). See also internal interface.


Fail-over is the process whereby a standby unit in a redundant system takes over when a software failure or hardware failure is detected on the active unit.

fail-over cable

The fail-over cable is the cable that directly connects the two units in a hardware-based redundant system.

fallback method

The fallback method is the third method in a load balancing hierarchy that the 3-DNS uses to load balance a resolution request. The 3-DNS uses the fallback method only when the load balancing modes specified for the preferred and alternate methods fail. Unlike the preferred method and the alternate method, the fallback method uses neither server nor virtual server availability for load balancing calculations. See also preferred method, alternate method.

FDDI (Fiber Distributed Data Interface)

FDDI is a multi-mode protocol for transmitting data on optical-fiber cables at speeds up to 100 Mbps.

Global Availability mode

Global Availability is a static load balancing mode that bases connection distribution on a particular server order, always sending a connection to the first available server in the list. This mode differs from Round Robin mode in that it searches for an available server always starting with the first server in the list, while Round Robin mode searches for an available server starting with the next server in the list (with respect to the server selected for the previous connection request).

hops factory

A hops factory is a type of factory run by the big3d agent that collects hops data about network paths.


A host is a network server that manages one or more virtual servers that the 3-DNS uses for load balancing.

ICMP (Internet Control Message Protocol)

ICMP is an Internet communications protocol used to determine information about routes to destination addresses, such as virtual servers managed by 3-DNS systems and BIG-IP systems.

internal interface

An internal interface is a network interface that can be accessed from a local-area network (LAN). See also external interface.


The iQuery protocol is used to exchange information between 3-DNS systems, BIG-IP systems, EDGE-FX Caches, and GLOBAL-SITE systems. The iQuery protocol is officially registered with IANA for port 4353, and works on UDP and TCP connections.

Kilobytes/Second mode

The Kilobytes/Second mode is a dynamic load balancing mode that distributes connections based on which available server currently processes the fewest kilobytes per second.

Least Connections mode

The Least Connections mode is a dynamic load balancing mode that bases connection distribution on which server currently manages the fewest open connections.

load balancing methods

Load balancing methods are the settings that specify the hierarchical order in which the 3-DNS uses three load balancing modes. The preferred method specifies the first load balancing mode that the 3-DNS tries, the alternate method specifies the next load balancing mode to try if the preferred method fails, and the fallback method specifies the last load balancing mode to use if both the preferred and the alternate methods fail.

load balancing mode

A load balancing mode is the way in which the 3-DNS determines how to distribute connections across an array.

local DNS

A local DNS is a server that makes name resolution requests on behalf of a client. With respect to the 3-DNS, local DNS servers are the source of name resolution requests. Also referred to as LDNS.

metrics information

Metrics information is the data that is typically collected about the paths between BIG-IP systems, EDGE-FX Caches or GLOBAL-SITE systems, and local DNS servers. Metrics information is also collected about the performance and availability of virtual servers. Metrics information is used for load balancing, and it can include statistics such as round trip time, packet rate, and packet loss.

MindTerm SSH

MindTerm SSH is the third-party application on 3-DNS systems that uses SSH for secure remote communications. SSH encrypts all network traffic (including passwords) to effectively eliminate eavesdropping, connection hijacking, and other network-level attacks. SSH also provides secure tunneling capabilities and a variety of authentication methods.

name resolution

Name resolution is the process by which a name server matches a domain name request to an IP address, and sends the information to the client requesting the resolution.

name server

A name server is a server that maintains a DNS database, and resolves domain name requests to IP addresses using that database.


The named daemon manages domain name server software.


NameSurfer is the third-party application on 3-DNS systems that automatically manages DNS zone files, synchronizing them with the configuration on the 3-DNS. NameSurfer automatically updates any configuration changes that you make using the Configuration utility. NameSurfer also provides a graphical user interface for DNS zone file management.

Network Time Protocol (NTP)

Network Time Protocol functions over the Internet to synchronize system clocks to Universal Coordinated Time. NTP provides a mechanism to set and maintain clock synchronization within milliseconds.

NS record

A name server (NS) record is used to define a set of authoritative name servers for a DNS zone. A name server is considered authoritative for some given zone when it has a complete set of data for the zone, allowing it to answer queries about the zone on its own, without needing to consult another name server.

packet rate

The packet rate is the number of data packets per second processed by a server.

Packet Rate mode

The Packet Rate mode is a dynamic load balancing mode that distributes connections based on which available server currently processes the fewest packets per second.


A path is a logical network route between a data center server and a local DNS server.

path probing

Path probing is the collection of metrics data, such as round trip time and packet rate, for a given path between a requesting LDNS server and a data center server.


On a 3-DNS, persistence is a series of related requests received from the same local DNS server for the same wide IP name. When persistence is turned on, a 3-DNS sends all requests from a particular local DNS server for a specific wide IP to the same virtual server, instead of load balancing the requests.


Picks represent the number of times a particular virtual server is selected to receive a load balanced connection.


A pool is a group of virtual servers managed by a BIG-IP, an EDGE-FX Cache, or a host. The 3-DNS load balances among pools (using the Pool LB Mode), as well as among individual virtual servers.

pool ratio

A pool ratio is a ratio weight applied to pools in a wide IP. If the Pool LB mode is set to Ratio, the 3-DNS uses each pool for load balancing in proportion to the weight defined for the pool.

preferred method

The preferred method specifies the first load balancing mode that the 3-DNS uses to load balance a resolution request. See also alternate method, fallback method.

principal 3-DNS

A 3-DNS that initiates metrics collection by the big3d agents and distributes the metrics to other members of a sync group. See also receiver 3-DNS.

probe protocol

The probe protocol is the specific protocol used to probe a given path and collect metrics information for the path. The probe protocols available on the 3-DNS are: ICMP, DNS_REV, DNS_DOT, UDP, and TCP. The probe protocols that are available change based on the data center server type.


A prober is a specific thread of the big3d agent that is used for path probing of a given set of paths.

prober factory

A prober factory is a utility that collects metrics data, such as round trip time and packet rate, for a given path between a requesting LDNS and a data center server. Prober factories are managed by the big3d agent, which reports the path probing metrics to the 3-DNS. Prober factories can run on BIG-IP systems, EDGE-FX Caches, and GLOBAL-SITE systems.

production rule

A production rule, on the 3-DNS, can change system behavior under specific operating conditions. For example, a production rule can switch load balancing modes or can reroute network traffic to a specific set of servers. Production rules are based on triggers such as time of day or current network traffic load.

QOS equation

The QOS equation is the equation on which the Quality of Service load balancing mode is based. The equation calculates a score for a given path between a data center server and a local DNS server. The Quality of Service mode distributes connections based on the best path score for an available data center server. You can apply weights to the factors in the equation, such as round trip time and completion rate.

Quality of Service load balancing mode

The Quality of Service load balancing mode is a dynamic load balancing mode that bases connection distribution on a configurable combination of the packet rate, completion rate, round trip time, hops, virtual server capacity, kilobytes per second, and topology information.


A ratio is the parameter in a virtual server statement that assigns a weight to the virtual server for load balancing purposes.

Ratio mode

The Ratio load balancing mode is a static load balancing mode that distributes connections across an pool of virtual servers in proportion to the ratio weight assigned to each individual virtual server.

receiver 3-DNS

A receiver 3-DNS is a system, in a sync group, that receives metrics data that are broadcast from big3d agents, but does not initiate metrics collection. See also principal 3-DNS.

redundant system

A redundant system is a pair of systems that are configured for fail-over. In a redundant system, one system runs as the active unit and the other system runs as the standby unit. If the active unit fails, the standby unit takes over and manages resolution requests.

remote administrative IP address

A remote administrative IP address is an IP address from which a system allows shell connections, such as SSH, RSH, or Telnet.


The resolver is the client part of the Domain Name System. The resolver translates a program's request for host name information into a query to a name server, and translates the response into an answer to the program's request. See also name server.

resource record

resource record is a record in a DNS database that stores data associated with domain names. A resource record typically includes a domain name, a TTL, a record type, and data specific to that record type. See also A record, CNAME record, NS record.

reverse domains

A type of DNS resolution request that matches a given IP address to a domain name. The more common type of DNS resolution request starts with a given domain name and matches that to an IP address.

root name server

A root name server is a master DNS server that maintains a complete DNS database. There are approximately 13 root name servers in the world that manage the DNS database for the World Wide Web.

Round Robin mode

Round Robin mode is a static load balancing mode that bases connection distribution on a set server order. Round Robin mode sends a connection request to the next available server in the order.

round trip time (RTT)

Round trip time is the calculation of the time (in microseconds) that a local DNS server takes to respond to a ping issued by the big3d agent running on a data center server. The 3-DNS takes RTT values into account when it uses dynamic load balancing modes.

Round Trip Time mode

Round Trip Time is a dynamic load balancing mode that bases connection distribution on which virtual server has the fastest measured round trip time between the data center server and the local DNS server.

secondary DNS

The secondary DNS is a name server that retrieves DNS data from the name server that is authoritative for the DNS zone.

Setup utility

The Setup utility is a utility that takes you through the initial system configuration process. The Setup utility runs automatically when you turn on a 3-DNS for the first time.

site content

Site content is data (including text, images, audio, and video feeds) that is accessible to clients who connect to a given site. See also dynamic site content, static site content.

SNMP (Simple Network Management Protocol)

SNMP is the Internet standard protocol, defined in STD 15, RFC 1157, that was developed to manage nodes on an IP network.

sod (switch over daemon)

The sod daemon controls the fail-over process in a redundant system.


SSH is a protocol for secure remote login and other secure network services over a non-secure network.

standby unit

A standby unit is a system in a redundant system that is always prepared to become the active unit if the active unit fails.

static load balancing modes

Static load balancing modes base the distribution of name resolution requests to virtual servers on a pre-defined list of criteria and server and virtual server availability; they do not take current server performance or current connection load into account.

static site content

Static site content is a type of site content that is stored in HTML pages, and changes only when an administrator edits the HTML document itself.


A subdomain is a sub-section of a higher level domain. For example, .com is a high level domain, and is a subdomain within the .com domain.


A sub-statement is a logical section within a statement that defines a particular element in the statement. A sub-statement begins with the sub-statement name followed by an open brace ( { ) and ends with a closed brace ( } ). Everything between those braces is part of the sub-statement. Sub-statements typically define a group of related variables, such as the calculation coefficients used in Quality of Service load balancing.

sync group

A sync group is a group of 3-DNS systems that share system configurations and path metrics for data center servers and virtual servers. Sync groups have one principal 3-DNS, and may contain one or more receiver systems. The receiver systems obtain their configuration information from the principal system. See also principal 3-DNS, receiver 3-DNS.

time tolerance value

The time tolerance value is the number of seconds that one 3-DNS system's clock is allowed to differ in comparison to another 3-DNS system's clock, without the two clocks being considered out of sync.

Topology mode

The Topology mode is a static load balancing mode that bases the distribution of name resolution requests on the weighted scores for topology records. Topology records are used by the Topology load balancing mode to redirect DNS queries to the closest virtual server, geographically, based on location information derived from the DNS query message.

topology record

A topology record specifies a score for a local DNS server location endpoint and a virtual server location endpoint.

topology score

The topology score is the weight assigned to a topology record when the 3-DNS is filtering the topology records to find the best virtual server match for a DNS query.

topology statement

A topology statement is a collection of topology records.


Traceroute is the utility that the hops factory uses to calculate the total number of network hops between a local DNS server and a specific data center.

TTL (Time to Live)

The TTL is the number of seconds for which a specific DNS record or metric is considered to be valid. When a TTL expires, the server usually must refresh the information before using it again.


The unavailable is a status used for data center servers and virtual servers. When a data center server or virtual server is unavailable, the 3-DNS does not use it for load balancing.


The unknown status is used for data center servers and virtual servers. When a data center server or virtual server is new to the 3-DNS and does not yet have metrics information, the 3-DNS marks its status as unknown. The 3-DNS can use unknown servers for load balancing, but if the load balancing mode is dynamic, the 3-DNS uses default metrics information for the unknown server until it receives live metrics data.


The up status is used for data center servers and virtual servers. When a data center server or virtual server is up, the data center server or virtual server is available to respond to name resolution requests.

virtual server

A virtual server is a specific combination of a virtual IP address and virtual port, and is associated with a content site that is managed by a BIG-IP, EDGE-FX Cache, or host server.

watchdog timer card

The watchdog timer card is a hardware device that monitors the 3-DNS for hardware failure.

wide IP

A wide IP is a collection of one or more domain names that maps to one or more groups of virtual servers managed either by BIG-IP systems, EDGE-FX Caches, or by host servers. The 3-DNS load balances name resolution requests across the virtual servers that are defined in the wide IP that is associated with the requested domain name.

WKS (well-known services)

Well-known services are protocols on ports 0 through 1023 that are widely used for certain types of data. Some examples of some well-known services (and their corresponding ports) are: HTTP (port 80), HTTPS (port 443), and FTP (port 20).

WKS record

A WKS record is a DNS resource record that describes the services usually provided by a particular protocol on a specific port.


In DNS terms, a zone is a subset of DNS records for one or more domains.

zone file

In DNS terms, a zone file is a database set of domains with one or many domain names, designated mail servers, a list of other name servers that can answer resolution requests, and a set of zone attributes, which are contained in an SOA record.