I have my proxy running at home, but changes in my ISP makes impossible to connect to home (appears that only NAT opened connections are allowed) This affects not only mining proxy, emule, vnc, etc.
And where my other miners are located, internet is vía proxy. Only HTTP, and 80/443 port. I switched them to other pool thats accept getwork via 80 port, but wanna mine in only one pool (slushs), and centralize my profits.

[EDIT]
If outside home make an traceroute, or ping, can't reach my host. Appears that fails at 1 route after mi IP. And in a tracert from home to other IP  are an internal IP that appears to be the mother of conflict