The Default L2Switch Idle (1800secs) and hard (3600seconds) timeouts as set in
~/opendaylight/etc/opendaylight/karaf/58-l2switchmain.xml

<is-learning-only-mode>false</is-learning-only-mode>
<is-install-dropall-flow>true</is-install-dropall-flow>
<dropall-flow-table-id>0</dropall-flow-table-id>
<dropall-flow-priority>0</dropall-flow-priority>
<dropall-flow-idle-timeout>0</dropall-flow-idle-timeout>
<dropall-flow-hard-timeout>0</dropall-flow-hard-timeout>
<reactive-flow-table-id>0</reactive-flow-table-id>
<reactive-flow-priority>10</reactive-flow-priority>
<reactive-flow-idle-timeout>1800</reactive-flow-idle-timeout> <-- here
<reactive-flow-hard-timeout>3600</reactive-flow-hard-timeout> <--here

are unrealistic for a real network.

As a result of this Unwanted flows are stuck are for an unimaginable amount of time
because of this.

The default values can be 300/600 for idle and hard timeout.