Sometimes you might encounter a internal network configuration setup by your local network admins where certain ports are blocked.
If you can't access a certain port though and the network admins say everything is open you might want to see what iptables is doing.
I'd forgotten that iptables can limit certain ports from being used if you're trying to access you're Linux server from another server.
Here were some command I had to use to stop iptables and permanently disable it - if I needed to reboot my Linux box:
1006 netstat -ln -A inet
1008 iptables --list
1009 /etc/init.d/iptables stop
1010 iptables --list
1011 chkconfig --list
1012 chkconfig --list | grep iptables
1013 chkconfig --help
1014 chkconfig --level 2345 iptables off
1015 chkconfig --list | grep iptables