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@@ -13,7 +13,7 @@
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- purpose with or without fee is hereby granted, provided that the above
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- copyright notice and this permission notice appear in all copies.
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-
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- - THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
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+ - THE SOFTWARE IS PROVIDED "DAS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
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- REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
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- AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
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- INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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@@ -4448,6 +4448,40 @@ Dhcp4/subnet4 [] list (default)
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</section>
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+ <section id="dhcp4-subnet-selection">
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+ <title>How DHCPv4 server selects subnet for a client</title>
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+ <para>
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+ The DHCPv4 server differentiates between the directly connected clients,
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+ clients trying to renew leases and clients sending their messages through
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+ relays. For the directly connected clients the server will check the
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+ configuration of the interface on which the message has been received, and
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+ if the server configuration doesn't match any configured subnet the
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+ message is discarded.</para>
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+ <para>Assuming that the server's interface is configured with the 192.0.2.3
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+ IPv4 address, the server will only process messages received through
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+ this interface from the directly connected client, if there is a subnet
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+ configured, to which this IPv4 address belongs, e.g. 192.0.2.0/24.
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+ The server will use this subnet to assign IPv4 address for the client.
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+ </para>
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+ <para>
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+ The rule above does not apply when the client unicasts its message, i.e.
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+ is trying to renew its lease. Such message is accepted through any
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+ interface. The renewing client sets ciaddr to the currently used IPv4
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+ address. The server uses this address to select the subnet for the client
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+ (in particular, to extend the lease using this address).
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+ </para>
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+ <para>
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+ If the message is relayed it is accepted through any interface. The giaddr
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+ set by the relay agent is used to select the subnet for the client.
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+ </para>
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+ <note>
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+ <para>The subnet selection mechanism described in this section is based
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+ on the assumption that client classification is not used. The classification
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+ mechanism alters the way in which subnet is selected for the client,
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+ depending on the clasess that the client belongs to.</para>
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+ </note>
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+ </section>
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+
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<section id="dhcp4-std">
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<title>Supported Standards</title>
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<para>The following standards and draft standards are currently
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Marcin Siodelski