Saturday, March 07, 2009

Remoting, bindTo and IPAddress.Any

Just solved a fun problem. While running a .NET remoting server on my ubuntu box with multiple NICs I saw some strange behavior where the server would return an alternate IP address, and the client would attempt to re-connect (using a new Socket) to the new IP address. Problem being: the server was responding with its localhost address (, which the client was resolving to its own loopback adapter. See the problem yet?

It turns out that in the absence of a specific binding, the server binds to IPAddress.Any. When a client attempts to connect, it's redirected to the server's bound address. Unless client and server are hosted on the same physical machine, there's really no point in ever using the loopback adaptor... which makes it a strange choice for default.

The solution:
Before you create and register your TcpServerChannel, you need to set some options.
IDictionary properties = new Hashtable();
properties["bindTo"] = "dotted.quad.ip.address";
properties["port"] = port;
IChannel serverChannel = new TcpServerChannel(properties, new BinaryServerFormatterSinkProvider());
RemotingConfiguration.RegisterWellKnownServiceType(typeof(Explorer), "Explorer.rem", WellKnownObjectMode.SingleCall);

Voila! 'appiness should ensue...

PS. If for some reason the dotted quad doesn't appeal to your particular situation (e.g. load balancing), you can set two other properties instead:
properties["machineName"] = "";
properties["useIpAddress"] = false;

PPS. I think the client will make always two socket connections, A + B. A is used at the start to do some initialization and get the address for connection B. B is used for meat and bones of the operation, and finally A is used just before they're both closed.

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