Introduction

Welcome to Kea Bootp Hooks Library. This documentation is addressed to developers who are interested in the internal operation of the Bootp library. This file provides information needed to understand and perhaps extend this library.

This documentation is stand-alone: you should have read and understood the Kea Developer's Guide and in particular its section about hooks.

Now To Use libdhcp_bootp

Introduction

libdhcp_bootp is a hooks library which allows the processing of BOOTP queries following the RFC1497. Old RFC951 BOOTP queries without vendor extensions are not supported.

Configuring the DHCPv4 Module

It must be configured as a hook library for the desired DHCP server modules. Note that the bootp library is installed alongside the Kea libraries in "<install-dir>/lib" where <install-dir> is determined by the –prefix option of the configure script. It defaults to "/usr/local". Assuming the default value then, configuring kea-dhcp4 to load the bootp library could be done with the following Kea4 configuration:

"Dhcp4": {
    "hooks-libraries": [
        {   "library": "/usr/local/lib/libdhcp_bootp.so" },
        ...
    ]
}

No parameter is defined.

Internal operation

The first function called in load() located in the bootp_callouts.cc. It checks if the necessary parameter is passed and decodes the option configurations. unload() free the configuration.

Kea engine checks if the library has functions that match known hook point names. This library has two such functions: buffer4_receive and pkt4_send located in bootp_callouts.cc.

If the receive query has no dhcp-message-type option then it is a BOOTP one: the BOOTP client class and a DHCPREQUEST dhcp-message-type option are added to the BOOTP query.

On the outgoing side dhcp-message-type and other DHCP specific options are removed from the response. When the packed response is shorter than the BOOTP minimum size (300 octets) it is padded after the END option by nuls up to this size.

In case any other library sets the SKIP flag before pkt4_send, an exception with the message "the packet pack already handled" will be thrown, to indicate that the action can not be properly performed. To fix this, all other libraries which might set the SKIP flag must appear in the server configuration after this library.

Multi-Threading Compatibility

The Bootp hooks library is compatible with multi-threading.