As stated in subject, I believe Comcast blocks all traffic between its customers and public tor relay nodes. That is, the blocking is not limited to tor-related traffic, all other services / ports on the tor relay are blocked.

Background: I am running a lightning node, lightning is a layer 2 protocol to scale Bitcoin. Lightning nodes need to be connected to each other ideally 24/7. I was contacted by the operator of another Lightning node, complaining that he cannot connect to my node. He is Comcast customer, I am not. I was also running a tor relay on the same public IPv4 address.

I am pretty sure that the blocking is done by Comcast and is triggered by being in public list of tor relays. The blocking disappeared after I stopped my tor relay and restarted my router (thus getting a new external IPv4 address). After 1 day, I relaunched the tor relay, and the blocking reappeared a few hours later. It was also confirmed by the said operator of the lightning node, who said there were various rounds of blocking tor, customers complaining and Comcast lifting the block for some time, only to reinstate the blocking later.

Comcast thus discourages me and similar people from running tor relays, or at least forces me to run tor in bridge mode. So this is an insidious attack on tor. Note that Bitcoin is not particularly relevant, Comcast is blocking tor nodes, not bitcoin nodes. So even if you hate Bitcoin, note that the same problem could arise even if Bitcoin never existed: e.g. a self-hosted web server, whose owner wants to donate his free capacity to tor by running tor relay. By doing this, he prevents any Comcast customers from accessing his web server, and this consequence is not obvious at all.

Any ideas on how to combat this? I was thinking about including some false positives in tor relay list. Imagine including some Google servers' IP addresses - Comcast customers suddenly cannot connect to Google, unless Comcast stops this blocking... or simply whitelists Google. But those false positives sound ugly and a bit malicious, not sure it is a good idea.

I already wrote about this publicly, and also wrote a mail to EFF. Hope I am not spamming, I feel this is quite important issue and am a bit frustrated by the lack of attention it gets.