Most ISP blocking is pretty superficial, usually just at the DNS level, you should be fine in the vast majority of cases. While parsing for the SNI flag on the client hello is technically possible, it’s computationally expensive at scale, and generally avoided outside of enterprise networks.
Yeah, even if they miss your DNS request, the ISP can still do a reverse lookup on the destination IP you’re attempting to connect to and just drop the traffic silently. That is pretty rare though, at least in US, mainly because It costs money to enforce restrictions like that at scale, which means blocking things isn’t profitable. However, slurping up your DNS requests can allow them to feed you false error pages, littered with profitable ads, all under the guies of enforcing copyright protections.
You are absolutely correct, I should have lead with that. Encrypted client handshake means no one can see what certificate you are trying to request from the remote end of your connection, even your ISP.
However, It’s worth noting though that if I am your ISP and I see you connecting to say public IP 8.8.8.8 over https (443) I don’t need to see the SNI flag to know you’re accessing something at Google.
First, I have a list of IP addresses of known blocked sites, I will just drop any traffic destined to that address, no other magic needed.
Second, if you target an IP that isn’t blocked outright, and I can’t see your SNI flag, I can still try to reverse lookup the IP myself and perform a block on your connection if the returned record matches a restricted pattern, say google.com.
VPN gets around all of these problems, provided you egress somewhere less restrictive.
That makes sense! Believe it or not it’s actually easier for an ISP to block a whole country than select websites and services. We actually null route all Russian public IP space where I work, that would absolutely be plausible on a national scale as well.
It’s imperfect, you can get around it, but it catches 99% of normal users, which is the goal.
RANT: I hate the fact that my ISP can restrict access to certain sites
How can it possibly be, that an ISP, which I’m paying for gets to decid, which sites I’m allowed to have access to, and which not?...