OPTIONS:
1. Connect using a proxy/portal service that masks your WAN IP.
2. Connect to a VPN with split tunneling (ENA) disabled. Force all port 80 traffic through the tunnel.
3. If you have multiple WAN IP's, choose a different IP in your subnet assigned by your ISP. Pass all traffic outbound through your new IP with a dynamic source NAT rule over the new IP.
4. Powercycle your modem and see if your ISP assigns a new IP.
5. Cell Phone tethering.
6. Crack a neighbors AP and use their internet.
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TOOLS:
http://www.barracudalabs.com/results.php
http://www.mxtoolbox.com/
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Most likely what happened is your IP was probably blocked based on the subnet, meaning an administrator went to block someone who was banned/spammed that originated from very similar IP's within the same subnet and ended up blocking the entire subnet.
Example:
Your IP: 172.16.1.100
Admin Blocked: 172.16.1.0/24 or 172.16.1.*
-Brought to you buy your friendly neighborhood Barracuda Certified Security Engineer.