The A record is the ADDRESS resource record that a Link Controller 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.
In a redundant system, an active unit is a system 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.
The alternate method specifies the load balancing mode that the Link Controller uses to pick a virtual server if the preferred method fails. See also preferred method.
Any IP Traffic
Any IP Traffic is a feature that allows the Link Controller to load balance protocols other than TCP and UDP.
The big3d agent is a monitoring agent that collects metrics information about server performance and network paths between a Link Controller and a specific local DNS server. The Link Controller uses the information collected by the big3d agent for dynamic load balancing.
The bigpipe utility provides command line access to the Link Controller.
BIG/stat is a statistical monitoring utility that ships on the Link Controller. This utility provides a snap-shot of statistical information.
BIG/top is a statistical monitoring utility that ships on the Link Controller. This utility provides real-time statistical information.
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 http://www.isc.org/products/BIND.
A chain is a series of filtering criteria used to restrict access to an IP address. The order of the criteria in the chain determines how the filter is applied, from the general criteria first, to the more detailed criteria at the end of the chain.
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.
The Link Controller is configured with two default VLANs, one for each interface. One default VLAN is named internal and one is named external. See also VLAN.
default wildcard virtual server
A default wildcard virtual server has an IP address and port number of 0.0.0.0:0. or *:* or "any":"any". This virtual server accepts all traffic that does not match any other virtual server defined in the configuration.
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 http://www.f5.com/index.html, the domain name is f5.com.
dynamic load balancing
Dynamic load balancing modes use current performance information from each node to determine which node should receive each new connection. The different dynamic load balancing modes incorporate different performance factors such as current server performance and current connection load.
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 Ratio load balancing mode
Dynamic Ratio mode is like Ratio mode (see Ratio mode), except that ratio weights are based on continuous monitoring of the links and are therefore continually changing.
An external monitor is a user-supplied health monitor. See also, health check, health monitor.
The external VLAN is a default VLAN on the Link Controller. In a basic configuration, this VLAN has the administration ports locked down. In a normal configuration, this is typically a VLAN on which external clients request connections to internal servers.
Fail-over is the process whereby a standby unit in a redundant system takes over when a software failure or a hardware failure is detected on the active unit.
The fail-over cable directly connects the two controller units together in a redundant system.
Fastest mode is a dynamic load balancing mode that bases connection distribution on which server currently exhibits the fastest response time to node pings.
FDDI (Fiber Distributed Data Interface)
FDDI is a multi-mode protocol used for transmitting data on optical-fiber cables at speeds up to 100 Mbps.
floating self IP address
A floating self IP address is an additional self IP address for a VLAN that serves as a shared address by both units of a Link Controller redundant system.
Global Availability mode
Global Availability mode 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).
A health check is a Link Controller feature that determines whether a node is up or down. Health checks are implemented through health monitors. See also health monitor and external monitor.
A health monitor checks a node to see if it is up and functioning for a given service. If the node fails the check, it is marked down. Different monitors exist for checking different services. See also health check and external monitor.
A host is a network server that manages one or more virtual servers that the Link Controller 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 Link Controller systems.
The physical port on a Link Controller is called an interface. See also link.
The internal VLAN is a default VLAN on the Link Controller. In a basic configuration, this VLAN has the administration ports open. In a normal configuration, this is a network interface that handles connections from internal servers.
IPSEC (Internet Security Protocol) is a communications protocol that provides security for the network layer of the Internet without imposing requirements on applications running above it.
The iQuery protocol is used to exchange information between Link Controllers. The iQuery protocol is officially registered with IANA for port 4353, and works on UDP and TCP connections.
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.
A last hop is the final hop a connection took to get to the Link Controller. You can allow the Link Controller to determine the last hop automatically to send packets back to the device from which they originated. You can also specify the last hop manually by making it a member of a last hop pool.
Least Connections mode
Least Connections mode is a dynamic load balancing mode that bases connection distribution on which server currently manages the fewest open connections.
A link is a physical interface on the Link Controller connected to another physical interface in a network.
The link aggregation feature allows you to combine a number of links together to act as one interface.
Link Controller active unit
In a redundant system, the Link Controller active unit is the controller that currently load balances connections. If the active unit in the redundant system fails, the standby unit assumes control and begins to load balance connections.
Link Controller web server
The Link Controller web server runs on a Link Controller and hosts the Configuration utility.
A local DNS is a server that makes name resolution requests on behalf of a client. With respect to the Link Controller, local DNS servers are the source of name resolution requests. Local DNS is also referred to as LDNS.
load balancing mode
A load balancing mode is a particular method of determining how to distribute connections across links.
A loopback adapter is a software interface that is not associated with an actual network card. The nPath routing configuration requires you to configure loopback adapters on servers.
MAC (Media Access Control)
MAC is a protocol that defines the way workstations gain access to transmission media, and is most widely used in reference to LANs. For IEEE LANs, the MAC layer is the lower sublayer of the data link layer protocol.
A MAC address is used to represent hardware devices on an Ethernet network.
Member is a reference to a node when it is included in a particular pool. Pools typically include multiple member nodes.
Metrics information is the data that is typically collected about the paths between Link Controllers 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 is the third-party application on Link Controller 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.
minimum active members
The minimum active members is the number of members that must be active in a priority group in order for the Link Controller to send its requests to that group. If the number of active members falls below this number, requests are sent to the next highest priority group (the priority group with the next lowest priority number).
The Link Controller uses monitors to determine whether nodes are up or down. There are several different types of monitors and they use various methods to determine the status of a server or service.
monitor destination IP address or IP address:port
The monitor destination IP address or address:port for a user defined monitor is used mainly for setting up a node alias for the monitor to check. All nodes associated with that monitor will be marked down if the alias node (destination IP address:port) is marked down. See also node alias.
You create a monitor instance when a health monitor is associated with a node, node address, or port. It is the monitor instance that actually performs the health check, not the monitor.
A monitor template is a system-supplied health monitor that is used primarily as a template to create user-defined monitors, but in some cases can be used as is. The Link Controller includes a number of monitor templates, each specific to a service type, for example, HTTP and FTP. The template has a template type that corresponds to the service type and is usually the name of the template.
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.
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.
NAT (Network Address Translation)
A NAT is an alias IP address that identifies a specific node managed by the Link Controller to the external network.
A node is a specific combination of an IP address and port (service) number associated with a server in the array that is managed by the Link Controller.
A node address is the IP address associated with one or more nodes. This IP address can be the real IP address of a network server, or it can be an alias IP address on a network server.
A node alias is a node address that the Link Controller uses to verify the status of multiple nodes. When the Link Controller uses a node alias to check node status, it pings the node alias. If the Link Controller receives a response to the ping, it marks all nodes associated with the node alias as up. If the controller does not receive a response to the ping, the it marks all nodes associated with the node alias as down.
A node port is the port number or service name that is hosted by a specific node.
Node status indicates whether a node is up and available to receive connections, or down and unavailable. The Link Controller uses the node ping and health check features to determine node status.
Observed mode is a dynamic load balancing mode that bases connection distribution on a combination of two factors: the server that currently hosts the fewest connections and also has the fastest response time.
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 Link Controller and a local DNS server.
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 Link Controller.
A performance monitor gathers statistics and checks the state of a target device.
Persistence is a series of related connections received from the same client, having the same session ID. When persistence is turned on, a controller sends all connections having the same session ID to the same node, instead of load balancing the connections.
Picks represent the number of times a particular virtual server is selected to receive a load balanced connection.
A pool is composed of a group of network devices (called members). The Link Controller load balances requests to the nodes within a pool based on the load balancing method and persistence method you choose when you create the pool or edit its properties.
A pool ratio is a ratio weight applied to pools in a wide IP. If the Pool LB mode is set to Ratio, the Link Controller uses each pool for load balancing in proportion to the weight defined for the pool.
A port is represented by a number that is associated with a specific service supported by a host. Refer to the Services and Port Index for a list of port numbers and corresponding services.
port-specific wildcard virtual server
A port-specific wildcard virtual server is a wildcard virtual server that uses a port number other than 0. See wildcard virtual server.
Port mirroring is a feature that allows you to copy traffic from any port or set of ports to a single, separate port where a sniffing device is attached.
Predictive mode is a dynamic load balancing mode that bases connection distribution on a combination of two factors: the server that currently hosts the fewest connections, and also has the fastest response time. Predictive mode also ranks server performance over time, and passes connections to servers which exhibit an improvement in performance rather than a decline.
The preferred method specifies the first load balancing mode that the Link Controller uses to load balance a resolution request. See also alternate method.
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 link and a local DNS server. The Quality of Service mode distributes connections based on the best path score for an available link. 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 inbound 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.
You create a rate filter from the Configuration utility or command line utility. When you assign a rate class to a rate filter, a rate class determines the volume of traffic allowed through a rate filter. See also rate filter.
Rate filters consist of a basic filter with a rate class. Rate filters are a type of extended IP filter. They use the same IP filter method, but they apply a rate class, which determines the volume of network traffic allowed through the filter. See also rate class.
A ratio is a parameter that assigns a weight to a virtual server for load balancing purposes.
The Ratio load balancing mode distributes connections across an array of virtual servers in proportion to the ratio weights assigned to each individual virtual server.
Redundant system refers to a pair of controllers that are configured for fail-over. In a redundant system, there are two controller units, one running as the active unit and one running as the standby unit. If the active unit fails, the standby unit takes over and manages connection requests.
remote administrative IP address
A remote administrative IP address is an IP address from which a controller allows shell connections, such as Telnet or SSH.
A 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.
RFC 1918 addresses
An RFC 1918 address is an address that is within the range of non-routable addresses described in the IETF RFC 1918.
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 link. The Link Controller takes RTT values into account when it uses dynamic load balancing modes.
Round Trip Time mode
Round Trip Time mode is a dynamic load balancing mode that bases connection distribution on which virtual server has the fastest measured round trip time between the link and the local DNS server.
self IP address
Self IP addresses are the IP addresses owned by the Link Controller that you use to access the internal and external VLANs.
Service refers to services such as TCP, UDP, HTTP, and FTP.
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 system for the first time.
SNAT (Secure Network Address Translation)
A SNAT is a feature you can configure on the Link Controller. A SNAT defines a routable alias IP address that one or more nodes can use as a source IP address when making connections to hosts on the external network.
This feature allows the Link Controller to perform a SNAT automatically on any connection that is coming from the system's internal VLAN. It is easier to use than traditional SNATs and solves certain problems associated with traditional SNATs.
SNMP (Simple Network Management Protocol)
SNMP is the Internet standard protocol, defined in STD 15, RFC 1157, developed to manage nodes on an IP network.
Source processing means that the interface rewrites the source of an incoming packet.
spanning tree protocol (STP)
Spanning tree protocol is a protocol that provides loop resolution in configurations where one or more external switches is connected in parallel with the Link Controller.
SSH is a protocol for secure remote login and other secure network services over a non-secure network.
An SSL gateway is a gateway for decrypting HTTPS requests to an HTTP server and encrypting the reply.
A standby unit in a redundant system is a unit that is always prepared to become the active unit if the active unit fails.
State mirroring is a feature on the Link Controller that preserves connection and persistence information in a Link Controller redundant system.
static load balancing modes
Static load balancing modes base connection distribution on a pre-defined list of criteria and virtual server availability; they do not take current server performance or current connection load into account.
A sticky mask is a special IP mask that you can configure on the Link Controller. This mask optimizes sticky persistence entries by grouping more of them together.
You can define any interface as a member of a tagged VLAN. You can create a list of VLAN tags or names for each tagged interface.
A transparent node appears as a router to other network devices, including the Link Controller.
A trunk is a combination of two or more interfaces and cables configured as one link. See also link aggregation.
The unavailable status is used for links and virtual servers. When a link or virtual server is unavailable, the Link Controller does not use it for load balancing.
The unknown status is used for links and virtual servers. When a link or virtual server is new to the Link Controller and does not yet have metrics information, the Link Controller marks its status as unknown. The Link Controller can use unknown servers for load balancing, but if the load balancing mode is dynamic, the Link Controller uses default metrics information for the unknown server until it receives live metrics data.
The up status is used for links and virtual servers. When a link or virtual server is up, the link or virtual server is available to respond to process connections.
A user-defined monitor is a custom monitor configured by a user, based on a system-supplied monitor template. For some monitor types, you must create a user-defined monitor in order to use them. For all monitor types, you must create a user-defined monitor to change system supplied monitor default values.
A virtual address is an IP address associated with one or more virtual servers managed by the Link Controller.
A virtual port is the port number or service name associated with one or more virtual servers managed by the Link Controller. A virtual port number should be the same TCP or UDP port number to which client programs expect to connect.
Virtual servers are a specific combination of virtual address and virtual port, associated with a content site that is managed by a Link Controller or other type of host server.
VLAN stands for virtual local area network. A VLAN is a logical grouping of network devices. You can use a VLAN to logically group devices that are on different network segments.
A VLAN name is the symbolic name used to identify a VLAN. For example, you might configure a VLAN named marketing, or a VLAN named development. See also VLAN.
watchdog timer card
A watchdog timer card is a hardware device that monitors the Link Controller for hardware failure.
A wide IP is a collection of one or more domain names that maps to one or more groups of virtual servers managed by Link Controllers. The Link Controller load balances name resolution requests across the virtual servers that are defined in the wide IP that is associated with the requested domain name.
wildcard virtual server
A wildcard virtual server is a virtual server that uses an IP address of 0.0.0.0, * or "any". A wildcard virtual server accepts connection requests for destinations outside of the local network. Wildcard virtual servers are included only in Transparent Node Mode configurations.