Tunneled ssh session not working with iptables rule to reject all other input traffic other than the required one

Issue

• I am accessing vnc over tunneled ssh session using below document

How to connect securely to VNC via tunnel over SSH ?

• I have configured iptables rule to DROP all the connections after allowing required traffic

  cat /etc/sysconfig/iptables
  ...
  rules to allow required INPUT packets
  ...
  -A INPUT -j DROP
  ...

• VNC over ssh tunnel is accessed on localhost, still I am not able to connect it when DROP ALL rule is in place.