# class_cmds: Class Commands

This section describes the Class Commands hooks library, which exposes several control commands for manipulating client classes (part of the Kea DHCP servers' configurations) without the need to restart those servers. Using these commands it is possible to add, update, delete, and list client classes configured for a given server.

This library may only be loaded by the `kea-dhcp4` or the `kea-dhcp6` process.

The Class Commands hooks library is available to premium Kea customers only.

## class-add Command

The `class-add` command adds a new client class to the DHCP server configuration. This class is appended at the end of the list of classes used by the server and may depend on any of the already configured client classes.

The following example demonstrates how to add a new client class to the DHCPv4 server configuration:

    {
        "command": "class-add",
        "arguments": {
            "client-classes": [
                {
                    "name": "ipxe_efi_x64",
                    "test": "option[93].hex == 0x0009",
                    "next-server": "192.0.2.254",
                    "server-hostname": "hal9000",
                    "boot-file-name": "/dev/null"
                }
            ]
        }
    }

Note that the `client-classes` parameter is a JSON list, but it allows only a single client class to be present.

Here is the response to the `class-add` command in our example:

    {
        "result": 0,
        "text": "Class 'ipxe_efi_x64' added."
    }

## class-update Command

The `class-update` command updates an existing client class in the DHCP server configuration. If the client class with the given name doesn't exist, the server returns the result code of 3, which means that the server configuration is not modified and the client class does not exist. The `class-add` command must be used instead to create the new client class.

The `class-update` command has the same argument structure as the `class-add` command:

    {
        "command": "class-update",
        "arguments": {
            "client-classes": [
                {
                    "name": "ipxe_efi_x64",
                    "test": "option[93].hex == 0x0017",
                    "next-server": "0.0.0.0",
                    "server-hostname": "xfce",
                    "boot-file-name": "/dev/null"
                }
            ]
        }
    }

Here is the response for our example:

    {
        "result": 0,
        "text": "Class 'ipxe_efi_x64' updated."
    }

Any parameter of the client class can be modified with this command, except `name`. There is currently no way to rename the class, because the class name is used as a key for searching the class to be updated. To achieve a similar effect to renaming the class, an existing class can be removed with the `class-del` command and then added again with a different name using `class-add`. Note, however, that the class with the new name will be added at the end of the list of configured classes.

## class-del Command

The `class-del` is used to remove a particular class from the server configuration. The class to be removed is identified by name. The class is not removed if there are other classes depending on it; to remove such a class, the dependent classes must be removed first.

The following is a sample command removing the `ipxe_efi_x64` class:

    {
        "command": "class-del",
        "arguments": {
            {
                "name": "ipxe_efi_x64"
            }
        }
    }

Here is the response to the `class-del` command in our example, when the specified client class has been found:

    {
        "result": 0,
        "text": "Class 'ipxe_efi_x64' deleted."
    }

If the class doesn't exist, the result of 3 is returned.

## class-list Command

`class-list` is used to retrieve a list of all client classes. This command includes no arguments:

    {
        "command": "class-list"
    }

Here is the response of the server in our example, including the list of client classes:

    {
        "result": 0,
        "text": "2 classes found",
        "arguments": {
            "client-classes": [
                {
                    "name": "ipxe_efi_x64"
                },
                {
                    "name": "pxeclient"
                }
            ]
        }
    }

Note that the returned list does not contain full class definitions, but merely class names. To retrieve full class information, the `class-get` command should be used.

## class-get Command

`class-get` is used to retrieve detailed information about a specified class. The command structure is very simple:

    {
        "command": "class-get",
        "arguments": {
            "name": "pxeclient"
        }
    }

If the class with the specified name does not exist, the status code of 3 is returned. If the specified client class exists, the class details are returned in the following format:

    {
        "result": 0,
        "text": "Class 'pxeclient' definition returned",
        "arguments": {
            "client-classes": [
                {
                    "name": "pxeclient",
                    "only-if-required": true,
                    "test": "option[vendor-class-identifier].text == 'PXEClient'",
                    "option-def": [
                        {
                            "name": "configfile",
                            "code": 209,
                            "type": "string"
                        }
                    ],
                    "option-data": [ ],
                    "next-server": "0.0.0.0",
                    "server-hostname": "xfce",
                    "boot-file-name": "/dev/null"
                }
            ]
        }
    }

Note that the example above is DHCPv4-specific; the last three parameters are only returned by the DHCPv4 server and are never returned by the DHCPv6 server. Also, some of the parameters provided in this example may not be returned if they are not specified for the class. Specifically, `only-if-required`, `test`, and `option-def` are not returned if they are not specified for the class.