Will firewalls block my non-HTTP network protocol even if I use TCP port 80?

Question

I want to create a simple JSON-based protocol to allow my game to talk to my custom server, but I don't want embed it in HTTP.

If I send a custom text-based protocol request to my server on port 80, will firewalls block it for not using HTTP format, or do they only care about the port number?

I won't use the same server as a web server, so I don't care about losing port 80 for real web serving.

As a bit of clarification, I am mainly concerned with the typical home firewalls that most people might have, not a high-end corporate firewall.

Answer 1

Depends on the firewall's sophistication and its configuration.

Answer 2

They certainly could. In more ways than one.

For instance a lot of organization's firewall block all outgoing port 80 traffic apart from traffic from an organizational HTTP proxy server. But if one of your game clients (running on their network) tried to use the proxy, it would fail ... because your client doesn't implement HTTP.

A second for instance is that some firewalls allow traffic through, but watch the TCP packets that pass back and forth. If the firewall detects something that looks anomalous; e.g. non-HTTP traffic on port 80, they might just inject a packet to reset the TCP/IP connection.

The bottom line is that it is (at the very least) anti-social to attempt to "work around" firewall restrictions by sneaking through on port 80. It is likely to get you and/or your users into trouble over ISPs / organizational network use policy. It is likely to provoke retaliation in the form of IP range blocks targeting your server.

My advice ... don't do it.

P.S. this is not just about corporate networks. ISPs have network usage rules too.

Answer 3

Moved question to ServerFault.com: