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@@ -368,6 +368,84 @@ 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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DHCPv4-over-DHCPv6 support is implemented using cooperating
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