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<document>
  <properties>
    <title>Lateral UDP Discovery</title>
    <author email="asmuts@apache.org">Aaron Smuts</author>
  </properties>

  <body>
    <section name="Lateral UDP Discovery">
      <p>
		Rather than list all the other lateral servers in the configuration
		file, you can configure the TCP lateral to use UDP
		discovery.  In discovery mode, lateral TCP caches will broadcast
		to a multicast address and port, letting all listeners know where they are.
  	  </p>
	  <p>
		On startup each lateral will issue a special message requesting a
		broadcast from the other caches.  Normal broadcasts occur every
		30 seconds. (This is to be made configurable.)  Regions that don't
		receive, are running in send only mode, don't broadcast anything but requests.
  	  </p>
      <p>
	    When a lateral receives a discovery message it will try to add
	    the lateral to the nowait facade for the region.  If it already exists
	    nothing happens.  If a region is not configured to send laterally, nothing
		happens,  since it doesn't have a no wait.
  	  </p>
  	  <p>
  		This allows you to have the same configuration on every machine.
      </p>
      <subsection name="Configuration">
        <p>
          The configuration is fairly straightforward and is done in the
          auxiliary cache section of the <code>cache.ccf</code>
          configuration file.  In the example below, I created a TCP
          Lateral Auxiliary Cache referenced by <code>LTCP</code>.  It uses
          UDP Discovery to locate other servers.  It broadcasts to
          multicast address <code>228.5.6.8</code> and port <code>6780</code>.
          It listens to port <code>1110</code>. The UDP datagram time-to-live
          is 4. 
        </p>
        <source><![CDATA[
jcs.auxiliary.LTCP=org.apache.commons.jcs.auxiliary.lateral.socket.tcp.LateralTCPCacheFactory
jcs.auxiliary.LTCP.attributes=org.apache.commons.jcs.auxiliary.lateral.socket.tcp.TCPLateralCacheAttributes
jcs.auxiliary.LTCP.attributes.TcpListenerPort=1110
jcs.auxiliary.LTCP.attributes.PutOnlyMode=true
jcs.auxiliary.LTCP.attributes.UdpDiscoveryAddr=228.5.6.8
jcs.auxiliary.LTCP.attributes.UdpDiscoveryPort=6780
jcs.auxiliary.LTCP.attributes.UdpDiscoveryEnabled=true
jcs.auxiliary.LTCP.attributes.UdpTTL=4
        ]]></source>
      </subsection>
      <subsection name="Multi-homed hosts">
        <p>
          On machines that have several network interfaces, it might be
          desirable to fix the interface that is used for multicast.
          For this purpose, the network interface can be specified in the 
          configuration (see below).
        </p>
        <p>
          If the network interface is not specified, JCS tries to detect a 
          suitable interface. The selected interface is logged on INFO level.
          Search for the message "Using network interface" in your log file.
        </p>
        <source><![CDATA[
jcs.auxiliary.LTCP=org.apache.commons.jcs.auxiliary.lateral.socket.tcp.LateralTCPCacheFactory
jcs.auxiliary.LTCP.attributes=org.apache.commons.jcs.auxiliary.lateral.socket.tcp.TCPLateralCacheAttributes
jcs.auxiliary.LTCP.attributes.TcpListenerPort=1110
jcs.auxiliary.LTCP.attributes.PutOnlyMode=true
jcs.auxiliary.LTCP.attributes.UdpDiscoveryInterface=en0
jcs.auxiliary.LTCP.attributes.UdpDiscoveryAddr=228.5.6.8
jcs.auxiliary.LTCP.attributes.UdpDiscoveryPort=6780
jcs.auxiliary.LTCP.attributes.UdpDiscoveryEnabled=true
jcs.auxiliary.LTCP.attributes.UdpTTL=4
        ]]></source>
      </subsection>
    </section>
  </body>
</document>