problem with session replication in tomcat 5.5.23

[Gabriele Faelli]

Hi all,
I'm running tomcat 5.5.23 on two RHEL 5.6.
I'm having big trouble making the session replication working across these
two nodes.
I configured a cluster and it looks like working: each node discovers the
other one, I can see in the logs every received and transmitted ping.
Well, when I create a session in the logs there are no mention of sessions
being replicated and/or errors encounter while trying.
The applications running on tomcat have the <distributable/> entry in their
web.xml and this is the cluster config part of the server.xml:

<Cluster className="org.apache.catalina.cluster.tcp.SimpleTcpCluster"
                defaultMode="true"

managerClassName="org.apache.catalina.cluster.session.DeltaManager"
                manager.expireSessionsOnShutdown="false"
                manager.useDirtyFlag="false"
                manager.notifyListenersOnReplication="true"
                manager.notifySessionListenersOnReplication="true"
                manager.sendAllSessions="true">
        <Membership
className="org.apache.catalina.cluster.mcast.McastService"
                mcastAddr="228.0.0.4"
                mcastPort="45564"
                mcastFrequency="500"
                mcastDropTime="3000"/>
        <Receiver
className="org.apache.catalina.cluster.tcp.ReplicationListener"
                tcpListenAddress="192.168.199.101"
                tcpListenPort="4001"
                tcpSelectorTimeout="100"
                tcpThreadCount="6"/>
        <Sender
className="org.apache.catalina.cluster.tcp.ReplicationTransmitter"
                replicationMode="synchronous"
                ackTimeout="15000"
                waitForAck="true"
                autoConnect="true"/>
                <Valve
className="org.apache.catalina.cluster.tcp.ReplicationValve"

filter=".*\.gif;.*\.js;.*\.jpg;.*\.png;.*\.htm;.*\.html;.*\.css;.*\.txt;"/>
                <Deployer
className="org.apache.catalina.cluster.deploy.FarmWarDeployer"
                        tempDir="/tmp/war-temp/"
                        deployDir="/tmp/war-deploy/"
                        watchDir="/tmp/war-listen/"
                        watchEnabled="false"/>

                <ClusterListener
className="org.apache.catalina.cluster.session.ClusterSessionListener"/>
        </Cluster>

Any Idea? Where I'm wrong? I did something stupid for sure :)
I tried every configuration, suggest... well everything I found on the
official an unofficial documentation... I'm quite frustated :P
Thanks in advance
G.