Conntrack

connection-tracking

apt-get install conntrack

root@nagus:/proc/net#

connection tracking:

ip_conntrack

nat tracking:

nf_conntrack

conntrack - command line interface for netfilter connection tracking

             This is the default table.  It contains a list of all  currently
             tracked  connections  through  the  system.
  
      conntrack -L [table] [-z]            List connection tacking or expectation table
      conntrack -G [table] parameters      Search for and show a particular (matching) entry in  the  given table.
      conntrack -D [table] paramaters      Delete an entry from the given table.
      conntrack -I [table] parameters      Create a new entry from the given table.
      conntrack -U [table] parameters      Update an entry from the given table.
      conntrack -E [table] parameters      Display a real-time event log.
      conntrack -F [table]                 Flush the whole given table
      conntrack -C [table]                 Show the table counter.
      conntrack -S                         Show the in-kernel connection tracking system statistics.