[BIG-IP] Usage and properties of the node specified by the FQDN

Table of contents

Target environment
What is an FQDN node?
How to configure the FQDN node
FQDN setting item
Add FQDN node to Pool
Display in running-config
References

Target environment

BIG-IP Virtual Edition
- version 16.x.x

What is an FQDN node?

Since the IP address of the real server is non-fixed, you may want to specify the real server with a domain name instead of the IP address. At such times, you can achieve your goal by configuring the FQDN node.

How to configure the FQDN node

Select Local Traffic > Nodes > Node List in the Main panel. Click Create on the Node List screen.

The following New Node screen is displayed. You can create an FQDN node by selecting FQDN in General Properties > Address.

FQDN setting item

Auto Populate

BIG-IP queries the DNS server to resolve the domain name configured on the FQDN node.

The Auto Populate setting determines what happens when multiple IP addresses are returned by the DNS server as the IP address that corresponds to the domain name.

When Auto Populate is disabled, BIG-IP dynamically creates a node using only the first one of the IP addresses returned by the DNS server.

When Auto Populate is enabled, BIG-IP dynamically creates a node using all the IP addresses returned by the DNS server. For example, if the DNS server returns three IP addresses, BIG-IP will create three dynamic nodes.

An example

For example, suppose that three records of 192.168.75.10, 192.168.75.20, and 192.168.75.30 are registered for the domain name host1.mynetwork.local on the DNS server side.

# cat /var/named/chroot/var/named/mynetwork.local
...
host1            IN      A      192.168.75.10
host1            IN      A      192.168.75.20
host1            IN      A      192.168.75.30

In BIG-IP, the FQDN node is set as shown below, and Auto Populate is disabled.

If you check the Node List screen, you can see that the node is created automatically. At this time, the node created is only for the first one of the IP addresses returned by the DNS server.

Next, if you create an FQDN node with Auto Populate enabled, the node will be created for all the IP addresses returned by the DNS server, as shown below.

Interval

The Interval setting corresponds to the DNS cache retention time and is also the DNS query execution interval. The default is 3600 seconds.

If you check the Use TTL option, the DNS cache retention time is based on the TTL of the DNS record set on the DNS server side.

Down Interval

The Down Interval setting is the amount of time to wait before marking an FQDN node as down after a DNS query fails. The default is 5 seconds.

Add FQDN node to Pool

On the Pool settings screen, you can add the created FQDN node by selecting Resources > New Members and selecting FQDN Node List.

Note that you must also set Auto Populate when you add the FQDN node to the Pool.

If Auto Populate is disabled in the FQDN node settings, Auto Populate cannot be enabled when adding an FQDN node to the Pool.

If you have Auto Populate enabled in your FQDN node settings, you can enable or disable Auto Populate when you add an FQDN node to your Pool.

Display in running-config

The FQDN node and the dynamically created IP address node are displayed in running-config as shown below.

config # tmsh show running-config ltm node
ltm node _auto_192.168.75.10 {
    address 192.168.75.10
    ephemeral true
    fqdn {
        autopopulate enabled
        name host1.mynetwork.local
    }
    monitor none
    session monitor-enabled
}
ltm node _auto_192.168.75.20 {
    address 192.168.75.20
    ephemeral true
    fqdn {
        autopopulate enabled
        name host1.mynetwork.local
    }
    monitor none
    session monitor-enabled
}
ltm node _auto_192.168.75.30 {
    address 192.168.75.30
    ephemeral true
    fqdn {
        autopopulate enabled
        name host1.mynetwork.local
    }
    monitor none
    session monitor-enabled
}
ltm node host1.mynetwork.local {
    fqdn {
        autopopulate enabled
        name host1.mynetwork.local
    }
    monitor none
    state fqdn-up
}

The following is displayed for the Pool to which the FQDN node has been added.

config # tmsh show running-config ltm pool
ltm pool Pool_FQDN {
    members {
        _auto_192.168.75.10:http {
            address 192.168.75.10
            ephemeral true
            fqdn {
                autopopulate enabled
                name host1.mynetwork.local
            }
        }
        _auto_192.168.75.20:http {
            address 192.168.75.20
            ephemeral true
            fqdn {
                autopopulate enabled
                name host1.mynetwork.local
            }
        }
        _auto_192.168.75.30:http {
            address 192.168.75.30
            ephemeral true
            fqdn {
                autopopulate enabled
                name host1.mynetwork.local
            }
        }
        host1.mynetwork.local:http {
            fqdn {
                autopopulate enabled
                name host1.mynetwork.local
            }
            state fqdn-up
        }
    }
}