[3695] Guide update about multiple addresses on the same link.

doc/guide/dhcp4-srv.xml

@@ -377,11 +377,9 @@ It is anticipated that this form of usage will only be used when it is desired t
 temporarily override a list of interface names and listen on all interfaces.
   </para>
   <para>Some deployments of the DHCP servers require that the servers listen
-  on the interfaces with multiple IPv4 addresses configured. In some cases,
-  multiple instances of the DHCP servers are running concurrently and each
-  instance should be bound to a different address on the particular interface.
-  In these situations, the address to use can be selected by
-  appending an IPv4 address to the interface name in the following manner:
+  on the interfaces with multiple IPv4 addresses configured. In these situations,
+  the address to use can be selected by appending an IPv4 address to the interface
+  name in the following manner:
   <screen>
 "Dhcp4": {
     "interfaces-config": {
@@ -390,9 +388,24 @@ temporarily override a list of interface names and listen on all interfaces.
     ...
 }
   </screen>
-  Note that only one address can be specified on each interface.
   </para>
 
+  <para>If it is desired that the server listens on multiple IPv4 addresses assigned
+  to the same interface, multiple addresses can be specified for this interface
+  as in the example below:
+  <screen>
+"Dhcp4": {
+    "interfaces-config": {
+        "interfaces": [ <userinput>"eth1/10.0.0.1", "eth1/10.0.0.2"</userinput> ]
+    },
+    ...
+}
+  </screen>
+  </para>
+
+  <para>Alternatively, if the server should listen on all addresses for the particular
+  interface, an interface name without any address should be specified.</para>
+
   <para>Kea supports responding to directly connected clients which don't have
   an address configured on the interface yet. This requires that the server
   injects the hardware address of the destination into the data link layer
@@ -428,6 +441,20 @@ temporarily override a list of interface names and listen on all interfaces.
   default value <userinput>raw</userinput> is used.
   </para>
 
+  <para>Using UDP sockets automatically disables the reception of brodcast
+  packets from directly connected clients. This effectively means that the
+  UDP sockets can be used for relayed traffic only. When using the raw sockets,
+  both the traffic from the directly connected clients and the relayed traffic
+  will be handled. Caution should be taken when configuring the server to open
+  multiple raw sockets on the interface with several IPv4 addresses assigned.
+  If the directly connected client sends the message to the brodcast address
+  all sockets on this link will receive this message and multiple responses
+  will be sent to the client. Hence, the configuration with multiple IPv4
+  addresses assigned to the interface should not be used when the directly
+  connected clients are operating on that link. To use a single address on
+  such interface, the "interface-name/address" notation should be used.
+  </para>
+
   <note>
     <para>Specifying the value <userinput>raw</userinput> as the socket type,
     doesn't guarantee that the raw sockets will be used! The use of raw sockets