Manual Chapter : About Nodes

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Manual Chapter

About Nodes

Introduction to nodes

A node is a logical object on the BIG-IP® the BIG-IP system system that identifies the IP address of a physical resource on the network. You can explicitly create a node, or you can instruct the BIG-IP system to automatically create one when you add a pool member to a load balancing pool.

The difference between a node and a pool member is that a node is designated by the device’s IP address only (, while designation of a pool member includes an IP address and a service (such as 10.10.10:8).

A primary feature of nodes is their association with health monitors. Like pool members, nodes can be associated with health monitors as a way to determine server status. However, a health monitor for a pool member reports the status of a service running on the device, whereas a health monitor associated with a node reports status of the device itself.

Nodes are the basis for creating a load balancing pool. For any server that you want to be part of a load balancing pool, you must first create a node, that is, designate that server as a node. After designating the server as node, you can add the node to a pool as a pool member. You can also associate a health monitor with the node, to report the status of that server.

Creating a node

Local traffic pools use nodes as target resources for load balancing. A node is an IP address or a fully-qualified domain name (FQDN) that represents a server resource that hosts applications.

Note: An alternate way to create a node is to create a pool member. When you create a pool member, the BIG-IP system creates the corresponding node for you.
  1. On the Main tab, expand Local Traffic, and click Nodes.
    The Node List screen opens.
  2. Click the Create button.
    The New Node screen opens.
  3. For the Address field:
    1. If you want to specify the node by its IP address, click Nodes and type an IP address.
    2. If you want to specify the node by a fully-qualifed domain name (FQDN), click FQDN and type the node's FQDN.
  4. In the Configuration area of the screen, configure the settings as needed or retain the default values.
  5. If you chose FQDN for the Address setting, then in the FQDN area of the screen, configure the settings as needed or retain the default values.
  6. Click Finished.
    The screen refreshes, and the new node appears in the node list.

About the node address setting

This setting specifies the IP address of the node. If you are using a route domain other than route domain 0, you can append a route domain ID to this node address. For example, if the node address applies to route domain 1, then you can specify a node address of

About node status

At any time, you can determine the status of a node, using the BIG-IP Configuration utility. You can find this information by displaying the list of nodes and viewing the Status column, or by viewing the Availability property of a node.

The BIG-IP Configuration utility indicates status by displaying one of several icons, distinguished by shape and color:

  • The shape of the icon indicates the status that the monitor has reported for that node.
  • The color of the icon indicates the actual status of the node.
Tip: You can manually set the availability of a node with the Manual Resume attribute of the associated health monitor.

About server node state

A node in a server pool must be enabled in order to accept traffic. A node is a logical object on the BIG-IP system that identifies the IP address of a physical resource on the network.

When you disable a node, the BIG-IP system allows existing connections to time out or end normally. In this case, by default, the only new connections that the node accepts are those that belong to an existing persistence session.

Additional configuration options

A node object has several optional settings that you can configure.

Associating a health monitor with a node

Using the BIG-IP system, you can monitor the health or performance of your nodes by associating monitors with those nodes. This is similar to associating a monitor with a load balancing pool, except that in the case of nodes, you are monitoring the IP address, whereas with pools, you are monitoring the services that are active on the pool members.

The BIG-IP system contains many different pre-configured monitors that you can associate with nodes, depending on the type of traffic you want to monitor. You can also create your own custom monitors and associate them with nodes. The only pre-configured monitors that are not available for associating with nodes are monitors that are specifically designed to monitor pools or pool members rather than nodes.

Note: Any monitor that you associate with a node must reside either in partition Common or in the partition that contains the node.

There are two ways that you can associate a monitor with a node: by assigning the same monitor (that is, a default monitor) to multiple nodes at the same time, or by explicitly associating a monitor with each node as you create it.

About monitors and automatic node creation

If you create a pool member without first creating the parent node,the BIG-IP system automatically creates the parent node for you. Fortunately, you can configure the BIG-IP system to automatically associate one or more monitor types with every node that the BIG-IP system creates. This eliminates the task of having to explicitly choose monitors for each node.

Keep the following in mind when working with default monitors:

  • If a user with permission to manage objects in partition Common disables a monitor that is designated as the default monitor for nodes (such as the icmp monitor), this affects all nodes on the system. Ensure that the default monitor for nodes always resides in partition Common.
  • To specify default monitors, you must have the Administrator user role assigned to your user account.
  • If all nodes reside in the same partition, the default monitor must reside in that partition or in partition Common. If nodes reside in separate partitions, then the default monitor must reside in partition Common.

About monitors and explicit node creation

Sometimes, you might want to explicitly create a node, rather than having Local Traffic Manager create the node automatically. In this case, when you create the node, you can either associate non-default monitors with the node, or associate the default monitors with the node.

About node availability

You can specify the minimum number of health monitors that must report a node as being available to receive traffic before the BIG-IP system reports that node as being in an up state.

About the ratio weight setting

When you are using the Ratio load balancing method, you can assign a ratio weight to each node in a pool. The BIG-IP system uses this ratio weight to determine the correct node for load balancing.

Note that at least one node in the pool must have a ratio value greater than 1. Otherwise, the effect equals that of the Round Robin load balancing method.

About the connection rate limit setting

The connection rate limit setting specifies the maximum rate of new connections allowed for the node. When you specify a connection rate limit, the system controls the number of allowed new connections per second, thus providing a manageable increase in connections without compromising availability. The default value of 0 specifies that there is no limit on the number of connections allowed per second.

Additional FQDN options

A node object has some optional FQDN settings that you can configure.

About FQDN address types

When you use FQDNs to identify nodes, you must specify whether the FQDN of the node resolves to an IPv4 or IPv6 address.

About the Auto Populate option

The Auto Populate option specifies whether the system automatically creates ephemeral nodes using the IP addresses returned by the resolution of a DNS query for a node defined by an FQDN. The default value is Enabled.

When set to Enabled, the system generates an ephemeral node for each IP address returned in response to a DNS query for the FQDN of the node. Additionally, when a DNS response indicates the IP address of an ephemeral node no longer exists, the system deletes the ephemeral node.

When set to Disabled, the system resolves a DNS query for the FQDN of the node with the single IP address associated with the FQDN.

About query intervals

You can specify intervals for when a query occurs. The intervals vary depending on whether the DNS server is up or down.

When the DNS server is up, the associated monitor attempts to probe three times, and marks the server down if there is no response within the span of three times the interval value, in seconds. The default value, in seconds, is 3600. Note that instead of typing an interval, you can enable the Time to Live (Use TTL) option.

When the DNS server is down, the associated monitor continues polling as long as the server is down. The default value, in seconds, is 5.