Find a firewall in a network path

["Lorenzo Capanna" <lorenzo.capanna () gmail com>]

This is my situation:
The port 21 is filtered from network A to host B.
Port 21 is not generally filtered from network A ( I'm able to connect
to hosts different than B ).
Port 21 is not generally filtered in the host B. ( From networks
different than A I'm able to connect to B)
Port 80 is not filtered from network A to host B.

It seems that a firewall is blocking port 21 connection from network A
to host B.
The admins of the network A gateway and of the B host deny the
firewall rule presence.

Is there a way to identify the firewall in the network path from A to B?

Thanks in advance

Lorenzo Capanna