Bitcoin clients connect to other bitcoin nodes on TCP port 8333 by default. Some Bitcoin users have reported issues attempting to connect or receive connections to their bitcoin clients across port 8333, according to a latest report by CCN.



After spending an entire day in vain trying to open 8333, one AT&T U-verse (a bundled package similar to others offered by well-known Cable Companies/ISPs) customer approached customer support.



"After hours of phone calls and messaging AT&T finally told me the truth of what was going on, and only because I noticed it myself and demanded an answer. The internet is being routed through a DVR/cable box, and they confirmed the DVR also has a firewall."



The problem arises when the ISP has complete control over the hardware from the user's house to their router to the Internet. Many well-known providers will deliberately close a number of connection ports to facilitate what they believe to be the optimum level of service.



"Perhaps this is the driving force behind the inexplicable and massive decline in Bitcoin nodes. Bitcoin is being censored by the ISPs themselves, and they won't even tell you that. I had to get in touch with headquarters and threaten to rip it out of the wall to get a proper answer", the AT&T U-verse customer concluded.



However, the report points out that while some ISP may indeed be blocking port 8333, they are not singling that particular port out, and instead they are blocking ports en masse.



If users are uncertain whether their ISPs are blocking Bitcoin, they may choose to conduct an inbound port test. A web search of "port testing" will give users some free services to pick from. Performing a port scan on port 8333 on their own connection will let the users know if ISP is blocking it or not.



If the user's ISP does happen to block port 8333, there are a few solutions they can resort to. For starters, users can ask their ISP's to put the router into "Bridge Mode", which turns the ISPs hardware into nothing more than a simple connection to the Internet. A second option is to get a business account with the ISP. While these typically cost more money per month, they do come with additional benefits such as static IP Addresses, and higher bandwidth.



The report concludes stating:



"Are ISPs Intentionally Blocking Bitcoin? Probably not. It's safer to assume the ISPs are simply protecting their own network by limiting open ports to the ones the vast majority of consumer level people are using. There are options available to users of all levels to work around any perceived limitations ISPs place on connections, and there is a fantastic bitcoin community eager to help in any way they can."