使用wsDualHttpBinding超时通过Internet连接到WCF服务

Question

Still on the WCF learning curve:

I've set up a self-hosted WCF Service (WSDualHttpBinding), which works fine on my own computer, which resides behind a firewall. If I run the client on my own computer, everything works great.

Now I installed the client on a computer outside my network, and I'm trying to access the service via a dynamic DNS, like so: http://mydomain.dyndns.org:8000/MyService . My port forwarding issues were taken care of in a previous question ; I can now see the service is up in my browser.

But now when I try to run the client on the other machine, I get the following error message: "The open operation did not complete within the allotted timeout of 00:01:00. The time allotted to this operation may have been a portion of a longer timeout."

I have disabled security on the service, so that's not it. What else might be preventing the connection from happening?

Answer 1

There's a real problem with WSDualHttpBinding and the way most people are connected to the internet - being behind a router means, at least with IPv4, having NAT ruin the party, as you've already discovered.

With WSDualHttpBinding , you have two connections: From the client to the server, and from the server to the client.

Usually, the client-to-server connection isn't a big deal - that's how most communication is done over the internet. In your case, it seems that you were behind a firewall and you've opened/forwarded the needed ports. But that doesn't solve the problem of the second connection - from the server to the client. Basically what happens with that second connection is that the client acts as a server, and the server acts as a client. So you need to do the same port opening/forwarding with each and every client that connects to your service, because it also acts as a server! This is of course an unreasonable demand to make of every user of your service. That's why WSDualHttpBinding is more suited to server-to-server communications, where the setup is a one-time affair.

Instead of trying to get WSDualHttpBinding to work, I suggest you switch to NetTcpBinding . Since both WSDualHttpBinding and NetTcpBinding are WCF-only, Microsoft-only, proprietary connection schemes, you're not losing much in the way of interoperability. What you're gaining, on the other hand, is a lot:

1. NetTcpBinding uses only a single connection, from the client to the server, while allowing two way communication like WSDualHttpBinding . So there's no need to deal with port opening/forwarding on the client side - NAT is a non-issue.
2. The communication protocol is binary and is more compact than the plain-text XML used in WSDualHttpBinding . Less data transfer means a better performing service.
3. With NetTcpBinding , you can get instant notification of when a client disconnects, since a socket is closed. No need to wait for a HTTP timeout like you do with WSDualHttpBinding .
4. A single connection means there nothing that can go out of sync - with WSDualHttpBinding , one of the two connections may drop while the other may still be active, having only one way communication. WCF has a way of dealing with that, but it's better to just avoid the issue in the first place.

Switching to NetTcpBinding usually only requires a configuration change - the code remains the same. It's simple, it's fast, it's much less of a hassle and most importantly - it just works.