# Kea configuration

Depending on configuration backend chosen (see ), configuration mechanisms are different. The following sections describe details of the different configuration backends. Note that only one configuration backend can be used and its selection is made when the configure script is run.

## BIND 10 configuration backend

This legacy configuration backend allows Kea to use the former BIND10 framework. That framework and this Kea configuration backend is no longer supported by ISC. It is currently developed as part of the Bundy project (see Bundy homepage). See the Bundy project documentation regarding configuration.

## JSON configuration backend

JSON is the default configuration backend and the only one supported as of the 0.9 release. It assumes that the servers are started from the command line (either directly or using a script, see TODO for details). The JSON backend uses certain signals to influence Kea. The configuration file is specified upon startup using -c parameter.

### JSON syntax

Configuration files for DHCPv4, DHCPv6 and DDNS modules are defined in an extended JSON format. Basic JSON is defined in RFC 4627. Kea components use a slightly modified JSON, in that they allowing bash-style comments in the file: lines with the hash (#) character in the first column are comment lines and are ignored.

The configuration file consists of a single object (often colloquially called a map) started with a curly bracket. It comprises the "Dhcp4", "Dhcp6", "DhcpDdns" and/or "Logging" objects. It is possible to define additional elements, but they will be ignored. (That principle was chosen to ease configuration management.) For example, it is possible to define Dhcp4, Dhcp6 and Logging elements in a single configuration file that can be used to start both the DHCPv4 and DHCPv6 components. When starting, the DHCPv4 component will use Dhcp4 object to configure itself and the Logging object to configure logging parameters; it will ignore the Dhcp6 object.

For example, a very simple configuration for both DHCPv4 and DHCPv6 could look like this:

    # The whole configuration starts here.
    {

    # DHCPv4 specific configuration starts here.
    "Dhcp4": {
        "interfaces": [ "eth0" ],
        "valid-lifetime": 4000,
        "renew-timer": 1000,
        "rebind-timer": 2000,
        "subnet4": [{
           "pool": "192.0.2.1-192.0.2.200",
           "subnet": "192.0.2.0/24"
        }],
        ...
    },
    # DHCPv4 specific configuration ends here.

    # DHCPv6 specific configuration starts here.
    "Dhcp6": {
        "interfaces": [ "eth1" ],
        "preferred-lifetime": 3000,
        "valid-lifetime": 4000,
        "renew-timer": 1000,
        "rebind-timer": 2000,
        "subnet6": [{
           "pool": "2001:db8::/80",
           "subnet": "2001:db8::/64"
        }],
        ...
    },
    # DHCPv6 specific configuration ends here.

    # Logger parameters (that could be shared among several components) start here.
    # This section is used by both the DHCPv4 and DHCPv6 servers.
    "Logging": {
       "loggers": [{
            "name": "*",
            "severity": "DEBUG"
        }],
        ...
    }
    # Logger parameters end here.

    # The whole configuration structure ends here.
    }

More examples are available in the Kea source code in the `doc/examples` directory.

To avoid repetition of mostly similar structures, examples in the rest of this guide will showcase only the subset of parameters appropriate for a given context. For example, when discussing the IPv6 subnets configuration in DHCPv6, only subnet6 parameters will be mentioned. It is implied that remaining elements (the global map that holds Dhcp6, Logging and possibly DhcpDdns) are present, but they are omitted for clarity. Usually, locations where extra parameters may appear are denoted with an ellipsis.

### Simplified Notation

It is sometimes convenient to refer to specific element in the configuration hierarchy. Each hierarchy level is separated by a slash. If there is an array, a specific instance within that array is referred by a number in square brackets (with numbering starting at zero). For example, in the above configuration the valid-lifetime in Dhcp6 component can be referred to as Dhcp6/valid-lifetime, the first interface for the DHCPv4 server as Dhcp4/interfaces[0] and the pool in the first subnet defined in the DHCPv6 configuration as Dhcp6/subnet6[0]/pool.