02-dhcp.dox 3.27 KB
 Tomek Mrugalski committed Jan 27, 2012 1 /**  Tomek Mrugalski committed Mar 19, 2012 2  * @page dhcpv4 DHCPv4 Server Component  Tomek Mrugalski committed Jan 27, 2012 3  *  Tomek Mrugalski committed Mar 19, 2012 4 5 6 7 8 9 10 11 12  * BIND10 offers DHCPv4 server implementation. It is implemented as * b10-dhcp4 component. Its primary code is located in * isc::dhcp::Dhcpv4Srv class. It uses \ref libdhcp extensively, * especially isc::dhcp::Pkt4, isc::dhcp::Option and * isc::dhcp::IfaceMgr classes. Currently this code offers skeleton * functionality, i.e. it is able to receive and process incoming * requests and trasmit responses. However, it does not have database * management, so it returns only one, hardcoded lease to whoever asks * for it.  Tomek Mrugalski committed Jan 27, 2012 13  *  Tomek Mrugalski committed Mar 19, 2012 14 15 16 17 18 19  * DHCPv4 server component does not support direct traffic (relayed * only), as support for transmission to hosts without IPv4 address * assigned is not implemented in IfaceMgr yet. * * DHCPv4 server component does not use BIND10 logging yet. *  Tomek Mrugalski committed Jun 01, 2012 20 21 22  * @section dhcpv4Session BIND10 message queue integration * * DHCPv4 server component is now integrated with BIND10 message queue.  Tomek Mrugalski committed Jun 08, 2012 23 24 25 26 27 28 29 30 31 32  * The integration is performed by establishSession() and disconnectSession() * functions in isc::dhcp::ControlledDhcpv4Srv class. main() method deifined * in the src/bin/dhcp4/main.cc file instantiates isc::dhcp::ControlledDhcpv4Srv * class that establishes connection with msgq and install necessary handlers * for receiving commands and configuration updates. It is derived from * a base isc::dhcp::Dhcpv4Srv class that implements DHCPv4 server functionality, * without any controlling mechanisms. * * ControlledDhcpv4Srv instantiates several components to make management * session possible. In particular, isc::cc::Session cc_session  Tomek Mrugalski committed Jun 01, 2012 33  * object uses ASIO for establishing connection. It registers its socket  Tomek Mrugalski committed Jun 08, 2012 34 35 36  * in isc::asiolink::IOService io_service object. Typically, other components * (e.g. auth or resolver) that use ASIO for their communication, register their * other sockets in the  Tomek Mrugalski committed Jun 01, 2012 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54  * same io_service and then just call io_service.run() method that does * not return, until one of the callback decides that it is time to shut down * the whole component cal calls io_service.stop(). DHCPv4 works in a * different way. It does receive messages using select() * (see isc::dhcp::IfaceMgr::receive4()), which is incompatible with ASIO. * To solve this problem, socket descriptor is extracted from cc_session * object and is passed to IfaceMgr by using isc::dhcp::IfaceMgr::set_session_socket(). * IfaceMgr then uses this socket in its select() call. If there is some * data to be read, it calls registered callback that is supposed to * read and process incoming data. * * This somewhat complicated approach is needed for a simple reason. In * embedded deployments there will be no message queue. Not referring directly * to anything related to message queue in isc::dhcp::Dhcpv4Srv and * isc::dhcp::IfaceMgr classes brings in two benefits. First, the can * be used with and without message queue. Second benefit is related to the * first one: \ref libdhcp is supposed to be simple and robust and not require * many dependencies. One notable example of a use case that benefits from  Tomek Mrugalski committed Jun 08, 2012 55 56 57 58  * this approach is a perfdhcp tool. Finally, the idea is that it should be * possible to instantiate Dhcpv4Srv object directly, thus getting a server * that does not support msgq. That is useful for embedded environments. * It may also be useful in validation.  Tomek Mrugalski committed Mar 19, 2012 59  *  Tomek Mrugalski committed Jan 27, 2012 60  */