dhcp4.dox 3.4 KB
 Tomek Mrugalski committed Oct 12, 2012 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 /** @page dhcp4 DHCPv4 Server Component 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. 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. @section dhcp4-session BIND10 message queue integration DHCPv4 server component is now integrated with BIND10 message queue. 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 object uses ASIO for establishing connection. It registers its socket 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 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 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. @section dhcp4-config-parser Configuration Parser in DHCPv4 This parser follows exactly the same logic as its DHCPv6 counterpart. See \ref dhcp6-config-parser. @section dhcp4-config-inherit DHCPv4 configuration inheritance Configuration inheritance in DHCPv4 follows exactly the same logic as its DHCPv6 counterpart. See \ref dhcp6-config-inherit. */