Commit 34078418 authored by Marcin Siodelski's avatar Marcin Siodelski
Browse files

[3242] Added new section to bind10 guide about DHCPv4 subnet selection

parent f22c490b
......@@ -13,7 +13,7 @@
- purpose with or without fee is hereby granted, provided that the above
- copyright notice and this permission notice appear in all copies.
-
- THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
- THE SOFTWARE IS PROVIDED "DAS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
- REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
- AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
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......@@ -4448,6 +4448,40 @@ Dhcp4/subnet4 [] list (default)
</section>
<section id="dhcp4-subnet-selection">
<title>How DHCPv4 server selects subnet for a client</title>
<para>
The DHCPv4 server differentiates between the directly connected clients,
clients trying to renew leases and clients sending their messages through
relays. For the directly connected clients the server will check the
configuration of the interface on which the message has been received, and
if the server configuration doesn't match any configured subnet the
message is discarded.</para>
<para>Assuming that the server's interface is configured with the 192.0.2.3
IPv4 address, the server will only process messages received through
this interface from the directly connected client, if there is a subnet
configured, to which this IPv4 address belongs, e.g. 192.0.2.0/24.
The server will use this subnet to assign IPv4 address for the client.
</para>
<para>
The rule above does not apply when the client unicasts its message, i.e.
is trying to renew its lease. Such message is accepted through any
interface. The renewing client sets ciaddr to the currently used IPv4
address. The server uses this address to select the subnet for the client
(in particular, to extend the lease using this address).
</para>
<para>
If the message is relayed it is accepted through any interface. The giaddr
set by the relay agent is used to select the subnet for the client.
</para>
<note>
<para>The subnet selection mechanism described in this section is based
on the assumption that client classification is not used. The classification
mechanism alters the way in which subnet is selected for the client,
depending on the clasess that the client belongs to.</para>
</note>
</section>
<section id="dhcp4-std">
<title>Supported Standards</title>
<para>The following standards and draft standards are currently
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