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@@ -1,4 +1,4 @@
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-// Copyright (C) 2012-2015 Internet Systems Consortium, Inc. ("ISC")
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+// Copyright (C) 2012-2016 Internet Systems Consortium, Inc. ("ISC")
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this
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@@ -26,6 +26,8 @@ This library contains several crucial elements for the operation of the DHCP ser
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- isc::dhcp::HostMgr - manager for static reservations (a.k.a. host reservations).
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- isc::dhcp::D2ClientMgr - DHCP-DDNS (D2) client manager which is responsible for
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the communication between the DHCP server and the D2 component.
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+- isc::dhcp::Dhcp4o6IpcBase - common part (base class) of DHCPv4-over-DHCPv6
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+ inter server communication (aka IPC).
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@section leasemgr Lease Manager
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@@ -67,7 +69,7 @@ the \ref isc::dhcp::CfgMgr::getStagingCfg is called again a fresh/default
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The Configuration Manager stores previous configurations, i.e. configurations
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which occurred prior to the most current configuration. This is currently
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-unused (except for unit tests) by the deamons, but in the future this
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+unused (except for unit tests) by the daemons, but in the future this
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mechanism can be used to trigger a rollover of the server configuration
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to a last good configuration that the administrator prefers.
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@@ -92,7 +94,7 @@ database. This object must implement the \ref isc::dhcp::BaseHostDataSource
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interface and its implementation is specific to the type of storage
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holding the reservations. For example, the host data source managing
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host reservations in the MySQL database is required to establish
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-connection to the MySQL databse and issue specific queries. Once
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+connection to the MySQL database and issue specific queries. Once
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implemented, the \ref isc::dhcp::HostMgr::create method must be updated
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to create an instance of this datasource. Note, that this instance is
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created as "alternate host data source" as opposed to the primary data
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@@ -113,7 +115,7 @@ documentation.
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@section optionsConfig Options Configuration Information
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The \ref isc::dhcp::CfgOption object holds a collection of options being
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-sent to the client. Since each subnet comes with a distnict set of
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+sent to the client. Since each subnet comes with a distinct set of
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options, every \ref isc::dhcp::Subnet object holds its own copy of the
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\ref isc::dhcp::CfgOption object with specific options.
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@@ -137,7 +139,7 @@ that there may be cases when the server administrator doesn't specify
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any subnet configuration and only wants global options to be used.
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This is the case, when the DHCP server is used for stateless
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configuration, i.e. client's are not allocated an address or prefix,
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-and only stateless configruation is handed out.
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+and only stateless configuration is handed out.
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@section allocengine Allocation Engine
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@@ -242,7 +244,7 @@ reserved until the client using this address releases or the server
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assigns a different address for it.
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In order to resolve this conflict the Allocation Engine will refuse to
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-renew the lease for the client using the addres not reserved for it.
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+renew the lease for the client using the address not reserved for it.
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This client should fall back to the 4-way exchange and the Allocation
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Engine will assign a different address. As a result, the reserved
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address will be freed for the use of the client for which the reservation
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@@ -269,7 +271,7 @@ leases.
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The @c isc::dhcp::TimerMgr has been created to address the issue of
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processing expired leases according to the the dedicated timer.
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-Nevertheless, this concept is univeral and should be used for
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+Nevertheless, this concept is universal and should be used for
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all timers which need to be triggered asynchronously, i.e. independently
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from processing the DHCP messages.
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@@ -366,4 +368,103 @@ since expiration elapsed. These methods are executed periodically
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by the DHCP servers using the dedicated timers registered in the
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@c isc::dhcp::TimerMgr.
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+@section subnetSelect Subnet Selection
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+
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+An important service offered by this library is the subnet selection
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+from a query packet.
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+
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+@subsection dhcp4SubnetSelect DHCPv4 Subnet Selection
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+
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+Selectors (i.e., members of @c SubnetSelector class) are:
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+- incoming interface name
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+- gateway address - giaddr field
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+- client address - ciaddr field
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+- local address
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+- remote address
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+- option select - from the first Relay Agent Link Selection suboption or
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+ from a Subnet Selection option
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+- client classes - used to reject a matching rule and try next rules
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+
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+First use the option select, next if the message was relayed (not undefined
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+gateway address) use the gateway address as a subnet relay address.
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+
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+If a subnet was not already selected choose an address between:
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+
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+- if the gateway address is not undefined the gateway address
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+- if the client address is not undefined and the local address not the
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+ broadcast address (i.e., renew or rebind) the client address
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+- if the remote address is not undefined and the local address not the
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+ broadcast address (i.e., renew or rebind) the remote address
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+- at this point try the interface name as a subnet interface
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+- if the interface name does not select a subnet choose the interface address
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+ (last resort)
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+
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+Match the chosen address in a subnet address range.
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+
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+@subsection dhcp4o6SubnetSelect DHCPv4-over-DHCPv6 Subnet Selection
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+
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+Selectors (i.e., members of @c SubnetSelector class) are:
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+- incoming interface name
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+- gateway address - giaddr field (should be always undefined)
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+- client address - ciaddr field
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+- local address - set to the interface IPv4 address
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+- remote address - IPv6 address
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+- option select - from a Subnet Selection option
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+- first relay link address - (IPv6) undefined or the first relay link
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+ address which is not undefined or link local (i.e., usable)
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+- interface ID - (IPv6) when a relay message includes an interface ID
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+ relay option
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+- client classes - used to reject a matching rule and try next rules
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+
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+Check if DHCPv4-over-DHCPv6 is enabled for this particular subnet and
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+continue with the next subnet is if it is not.
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+
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+First the remote address is matched in a subnet IPv6 range, second
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+the interface ID if it is set is matched, third the interface name.
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+
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+These rules are applied for each subnet configuration so if two
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+subnets match the first one is returned (vs. the first matching rule).
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+
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+@todo better DHCPv4-over-DHCPv6 selection, e.g., handle relayed
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+messages and return best (vs first) match.
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+
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+@subsection dhcp6SubnetSelection DHCPv6 Subnet Selection
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+
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+Selectors (i.e., members of @c SubnetSelector class) are:
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+- incoming interface name
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+- remote address
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+- first relay link address - undefined or the first relay link address which
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+ is not undefined or link local (i.e., usable)
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+- interface ID - when a relay message includes an interface ID relay option
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+- client classes - used to reject a matching rule and try next rules
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+
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+If the first relay link address is undefined the client is directly connected:
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+the interface name is matched and if it does not select a subnet the remote
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+address is matched in a subnet address range.
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+
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+If the first relay link address is not undefined the query was relayed:
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+the interface ID is tried and if it does not select a subnet the first
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+relay address is matched as a subnet relay address.
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+
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+@section dhcp4o6Ipc DHCPv4-over-DHCPv6 Inter Process Communication
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+
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+DHCPv4-over-DHCPv6 support is implemented using cooperating
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+DHCPv6 and DHCPv6 servers. Servers communicate over a pair of
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+local UDP sockets using consecutive ports. The common part of
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+the Inter Process Communication (IPC) is provided by the base class
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+@c isc::dhcp::Dhcp4o6IpcBase.
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+
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+The receiving interface name and remote IPv6 address meta information
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+are conveyed within a Vendor Specific Information option with the ISC
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+enterprise ID carrying interface and remote address suboptions.
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+\ref isc::dhcp::Dhcp4o6IpcBase::send adds them,
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+\ref isc::dhcp::Dhcp4o6IpcBase::receive decodes and removes them.
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+
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+Also see \ref dhcpv4o6Dhcp4 and \ref dhcpv4o6Dhcp6 for details on how IPC
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+is used by DHCPv4 and DHCPv6 components.
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+
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+@todo
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+
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+DHCPv4-over-DHCPv6 which are relayed by a DHCPv6 relay are not yet supported.
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+
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*/
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Francis Dupont