RNDIS lost connection / lag issue

Question

We have a makeshift SOAP client written in C# connecting to a CXF service on a desktop from a windows mobile device. When this device is connected via ActiveSync, it creates a virtual adapter for the RNDIS connection. This virtual adapter assigns a gateway IP to the host, 169.254.2.2.

When we attempt to go through the connection with the hostname or the host's IP set as the address in the C# client, everything works perfectly. When we however set the IP to be the RNDIS gateway (169.254.2.2), the connection is periodically lost on the server side. The CXF service keeps trying to connect, and eventually succeeds, but this results in a massive slowdown of the connection. There are no errors reported in our logs on the mobile C# side, only on the CXF server.

Does anyone have any clues as to why this is happening? We need to assert that 169.254.2.2 cannot possibly be used as a valid endpoint before we rule it out.

Oh, and in case it helps, the C# client is granted the IP 169.254.2.1 through DHCP after the ActiveSync connection.

Answer 1

I found out the cause of this, but I feel bad for answering because I doubt there was any way someone else could have guessed that this was the problem:

On our CXF server, we have a call to InetAddress.getHostName() which basically does a reverse DNS lookup on the request sent from the C# client.

When using the ActiveSync IP address, there was no entry in the DNS for 169.254.2.1 (of course), so the java class would hang until the method timed out (which took about 20 seconds before it would write a response to the C# client). At 20 seconds per request, this resulted in the massive slowdown and lost connection errors.

We fixed this by moving the call to an executor thread that force-finished after half a second. Because it was in another thread, the slowdown became nonexistent. Glad to have that over with!

Answer 2

The first issue that comes to my head, especially once I saw that you are using DCHP, is that the lease time on the IP from the DHCP server is expiring and the CXF server is having to wait for the DCHP server to issue a new lease.

Try lengthening the DCHP lease if you know that the IP won't be changing and use a static IP if you are able. That will at least remove that point of failure.