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By default, Bitcoin clients connect to other bitcoin nodes on TCP port 8333. If a user wants their Bitcoin client to connect to other nodes, they will need to allow outgoing TCP connections on port 8333, and also will need to have the ability to accept connections on that same port.

Some Bitcoin users have reported issues attempting to connect or receive connections to their bitcoin clients across port 8333.

After spending an entire day effortlessly trying to get a bitcoin client working from a home computer, one AT&T Uverse customer called 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.

AT&T Uverse is a bundled package similar to what many of the other nationally known Cable Companies / ISPs are offering. Home Internet service along with your TV channels in one, with added benefits such as DVRs, streaming music, games, and much more.


Is AT&T trying to block Bitcoin?

Is AT&T trying to block Bitcoin?

The issue arises when the ISP is in full control of the hardware from your house to their router to the Internet. Many big name providers will intentionally close a slew of connection ports in order to provide what the company deems to be the best 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 disgruntled AT&T Uverse customer concluded.

Fear not, for all hope is not lost. While some ISP may indeed be blocking port 8333, they’re not singling that specific port out. The ISP are simply blocking ports en masse.

If users are unsure whether their ISPs are blocking Bitcoin, they may opt to perform an inbound port test. There are several web based services that will test an inbound connection on a specific port for you. A web search of “port testing” will give users a few different free services to choose from. Performing a port scan on port 8333 on your own connection will let you know if your ISP is blocking it or not.

If the user’s ISP does happen to block port 8333, there are a few solutions they can turn to, all of which require a little bit of effort and technical ability on the end users part.

For starters, users can ask their ISP’s to put the router into “Bridge Mode”. This turns the ISPs hardware into nothing more than a simple connection to the Internet. The user would be required to provide their own router, and to handle the configuration and maintenance of that hardware. The downside is that many ISPs limit technical support when a home user requests their router be put into Bridge Mode.

A second option, very similar to Bridge Mode, 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. Depending on the provider, business account may or may not come with their own Router, so users must be prepared to manage their own hardware with this scenario as well.

If users are concerned with telling their ISPs that they’re running a Bitcoin client, it just so happens that a few other well known services use port 8333. Instead of revealing any information about Bitcoin, users may tell their ISPs they’re running the VMWare Server Management User Interface, or the Y-Cam Wireless IP Camera.

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.

Images from Shutterstock.


Posted by Andy Stetzinger

Andy Stetzinger is a 20 year IT veteran, and has had the unique opportunity to work within the emerging technology field proving business and technical analysis to some of the World’s greatest companies. Andy specializes in providing business solutions through creative thinking and the proper implementation of technical resources.


  1. None of my ports work for bitcoin, they are all hidden via a private subnet, so literally the internet cannot see them. They use one of the few private IPs available, completely non-routable for other computers trying to connect directly ( ) I’m still working on this and will send another email describing how I fixed this hopefully soon… and if it’s unfixable I will update anyways since I’ve learned alot since the first email about how Bitcoin is blocked in multiple ways.Trying to use a public subnet now, and ive been exploring every possible program on windows and the router which might interfere with connections

  2. Ivo Oscar Faleiro 02/09/2015 at 06:28

    Yes … 99% ISPS are intentionally blocking Bitcoin transactions.

  3. Ivo Oscar Faleiro 02/09/2015 at 06:27

    99% ISPS are

  4. Or, you could just set your bitcoin clients/daemons to use a non-standard port, like I’ve been doing for years… .. .

  5. Comcast was NOTORIOUS for these medieval shenanigans. Namely, throttling user’s traffic. Reminds me of this video: It’s funny because it’s true!

  6. Philip Spicer 01/09/2015 at 22:47

    Thanks Michael . If you have any more support tips they are welcome

  7. You can change the default listen port of your bitcoin-qt client:
    -port= Listen for connections on (default: 8333 or testnet: 18333)

  8. Philip Spicer 01/09/2015 at 19:17

    just explained why my Bitcoin client was not working properly – Thanks

  9. Neal Gafter 01/09/2015 at 18:46

    “After spending an entire day effortlessly trying to get a bitcoin client working from a home computer…” Did he really spend the day without effort, or was it rather that he did not benefit from the fruit of his labor? Perhaps the word you were looking for was fruitlessly?

  10. Milly Bitcoin 01/09/2015 at 18:26

    The damn Leviathan!!!

  11. Milly Bitcoin 01/09/2015 at 18:24

    Comcast did that to me but it was only about $10/month extra. I ended up getting fixed IP and grater bandwidth so now I am up to $125/month just for Internet. It is interesting how a security issue can be solved by the customer paying a higher monthly fee.

  12. Tampa Steve 01/09/2015 at 18:11

    Home service has very strict guidelines. This typically includes any sort of hosting be it FTP, HTTP, P2P or other. In the past I made the mistake of saying I needed to be able to remote into my desktop from the office so I could transfer files. They flagged my account and tried to force me to go to a business plan that was an additional 75$ on top of the standard home user fee for the package I had at the time. ended up having to cancel service and go with a different ISP for a while. Just be cautious what you say to your ISP. Almost all home service TOS state no commercial or business traffic is approved for use on a home connection (obviously buying stuff is not against the TOS but if they wanted to be jerks selling could be”.

  13. concerndcitizen 01/09/2015 at 18:03

    Ah, no, it’s not likely they are just doing this to “improve service”. They routinely block various sites and use traffic shaping methods to keep you from finding out the truth.

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