This package provides classes for manipulating DHCP Packets: creating, parsing and sending. It is suitable for DHCP client, servers, relays or analysis. It currently supports only IPv4.

DHCPPacket is the central class allowing manipulation of DHCP packets. A generic framework for DHCP servers is also availaible, on a development model similar to HTTP Servlets.

Packet manipulation

Basic functions includes packet creation, modification, parsing and sending on the wire.

It is centered around the 3 following classes:

DHCPPacket packet data manipulation
DHCPConstants commonly used DHCP constants (better used through static imports) import static sf.dhcp4java.DHCPConstants.*;tt>
DHCPOption DHCP option manipulation, it is used internally since DHCPPacket provides helper functions. It is however useful if you want to create options lists and set them at once instead of one by one.

There are two basic ways to build a new DHCPPacket object.

First one is to build an object from scratch using the constructor and setters.

DHCPPacket discover = new DHCPPacket();
discover.setOp(DHCPPacket.BOOTREQUEST);
discover.setHtype(DHCPPacket.HTYPE_ETHER);
discover.setHlen((byte) 6);
discover.setHops((byte) 0);
discover.setXid( (new Random()).nextInt() );
...

Second is to decode a DHCP datagram received from the network. (simple DHCP sniffer). In this case, the object is created through a singleton factory

DatagramSocket socket = new DatagramSocket(67);
while (true) {
    DatagramPacket pac = new DatagramPacket(new byte[1500], 1500);
    socket.receive(pac);
    DHCPPacket dhcp = DHCPPacket.getPacket(pac);
    System.out.println(dhcp.toString());
}

DHCP Servlets

This package also contains a basic framework for implementing a DHCP server.

Note: this package does not contain a full blown DHCP server but only a framework with simple examples.

This framework is very close to the HTTP Servlet framework.

DHCP Servlet

The DHCPServlet is based on a request/response model. The DHCPPacket service(DHCPPacket) is called with the incoming packet from client. This method should return either the response DHCP packet (including address/port for sending) or null to silently ignore the request.

The service() method is systematically called, and dispatches control to more specific methods as its default behaviour.

doDiscover(), doRequest(), doInform(), doDecline(), doRelease()

Note: only valid DHCP datagrams are passed to servlets. Invalid packets are discarded. However, you can override DatagramPacket serviceDatagram(DatagramPacket) if you want a chance to treat every datagram received even malformed.

DHCP Server

The DHCP Server provided is based on a multi-thread model. The main thread listens at the socket, then dispatches work to a pool of threads running the servlet.

Configuration: the Server reads the following properties in "/DHCPd.properties" at the root of the class path. You can however provide a properties set when contructing the server. Default values are:

serverAddress=127.0.0.1:67 [address:port]
serverThreads=2 [number of concurrent threads for servlets]

Standard way of running the Server:

    public static void main(String[] args) {
        try {
            DHCPServer server = DHCPServer.initServer(new TrivialDHCPServlet(), null);
            new Thread(server).start();
        } catch (ServerInitException e) {
            // die gracefully
        }
    }