« conntrack provides a full featured userspace interface to the netfilter connection  tracking  system  that  is  intended  to  replace  the  old /proc/net/ip_conntrack  interface.  This  tool  can  be used to search, list, inspect and maintain the connection  tracking  subsystem  of  the Linux  kernel.   Using  conntrack  ,  you  can dump a list of all (or a filtered  selection of) currently tracked connections, delete connections from the state table, and even add new ones.

[...]

TABLES

       The connection tracking subsystem maintains two internal tables:

       conntrack:
              This is the default table.  It contains a list of all  currently
              tracked  connections  through  the  system.   If  you  don’t use
              connection tracking exemptions (NOTRACK iptables  target),  this
              means all connections that go through the system.

       expect:
              This   is   the  table  of  expectations.   Connection  tracking
              expectations  are  the  mechanism  used  to   "expect"   RELATED
              connections  to  existing ones.  Expectations are generally used
              by "connection tracking helpers" (sometimes  called  application
              level  gateways  [ALGs]) for more complex protocols such as FTP,
              SIP, H.323.

[...]

       -L --dump
              List connection tacking or expectation table

       -C, --count
              Show the table counter.

       -S, --stats
              Show the in-kernel connection tracking system statistics. »

Pour les états NAT :
«       -n, --src-nat
              Filter source NAT connections.

       -g, --dst-nat
              Filter destination NAT connections.

       -j, --any-nat
              Filter any NAT connections. »

L'erreur « Can't open /proc/sys/net/netfilter/nf_conntrack_count » signifie que le module « nf_conntrack » n'est pas chargé, probablement car vous n'avez aucune règle netfilter qui utilise les états/le suivi des connexions.