Is it possible to block BTC related traffic in a firewall?

[johnyj]

If I block port 8333, will it still work?

Or simply, can I use port 80 in a node?

[Schleicher]

It depends on how restrictive the firewall is.
Usually it doesn't matter what port your client uses.
If port 80 is not being blocked then you only need someone running a client on port 80 to connect to it.

[celkaris]

layer 7 filtering : http://l7-filter.sourceforge.net/

[johnyj]

It depends on how restrictive the firewall is.
Usually it doesn't matter what port your client uses.
If port 80 is not being blocked then you only need someone running a client on port 80 to connect to it.

If a client is running on port 80, will it be able to connect to rest of the network?

[Schleicher]

If a client is running on port 80, will it be able to connect to rest of the network?

It's the other way around.
It will only connect when someone else has a client running on port 80.
That's assuming the firewall is not being totally paranoid.

[Buffer Overflow]

If I block port 8333, will it still work?

Depends. Are you blocking the incoming or outgoing packets?

[tpantlik]

You can use tor to bypass firewall blocking bitcoin port. And even if it is actively trying to block tor you can still try to connect with tor bridge.

[Buffer Overflow]

If a client is running on port 80, will it be able to connect to rest of the network?

Ports 0 - 1023 are special ports that would require your Bitcoin client to be running at elevated root privilege. (Bad idea.)

Bitcoin won't bind to port 80 as a normal user.

[johnyj]

Thanks, just want to evaluate the risk of a block at major back-bone switch. Google and youtube are totally blocked in main land china, so I suppose it is not very difficult for government to do such a block if they decided to do so

[gmaxwell]

Bitcoin isn't an anti-censorship system— it's trivial to block.

If you're concerned about bitcoin being blocked setup and maintain a Bitcoin node on a tor hidden service (see doc/Tor.txt), we could use some more of them.

[celkaris]

if your problem is about censorship, you oculd have a look at "BoF" project, haven't tried it, but it may help.

Bof = "Bitcoin over Freenet" ; you probably already heard about Freenet [ http://freenetproject.org/ ]  if you live in china & are concerned by censorship.

Can't link to USK here, but you'll find the link from most index freesites.