Block directory authorities, is it possible?

[Kevin Smith]

> I wonder if it's just an oversight that tor.eff.org hasn't been blocked
> in your case?

I don't think it is an oversight that tor.eff.org has not been blocked
in my case. I have never heard of the Tor site being blocked anywhere
in China. My friends in Beijing, Shanghai and Shandong province are
able to access it and I was able to access it continuously for three
years in Shandong when I lived there.

> How does the blocking with your ISP work? Do you get a generic reject
> page telling you the service is blocked? Do you get TCP resets?

When a page is blocked it usually looks like it has timed out. I'm not
clear as to how the blocking works. It seems that sensitive keywords
in a webpage trigger the firewall to send a TCP reset to both the
client and the server(1), but I do not know how specific IP addresses
are blocked. I guess the routers at the great firewall just stop the
client's request from reaching the server at that specific IP address
and that the router at the firewall doesn't send any response back to
the client so that it looks like a timeout. Someone please correct me
if I'm wrong about this.

(1) http://www.andrewlih.com/blog/2006/06/27/great-firewall-filtering-revealed/

Kevin S.