amanda won't work through firewalls unless the package is configured
at build time with the following options:
Well, you really want to use --withtcpportrange=aaa,bbb
--with-udpportrange=ccc,ddd, and selet the values of aaa,bbb,ccc and
ddd that are large enough to back up your enterprise, but not so
large as to make the firewall administrator whimper. Oh, and you
need to build all of your Amanda clients with set of portranges that
you use on your server.
The real solution would be for the portranges to be configured in
the amanda.conf file on the server. This enhancement is somewhere
on my very long list of "things to do some day".