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RDP protocol error (Return code: 516)
#1
When connecting to a particular remote machine FROM a 2008 R2 server, we are getting a Windows Sockets connect failed message.

We are able to connect to other servers from the 2008 server and are able to connect to the particular remote from Vista, Win7, XP, 2003 server etc.
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#2
Maybe something simple like wrong network configuration, name resolution, firewall, authentication, etc.?
Some special configuration on the “problem” servers that is diffrent from the working ones?
Can you connect to the "problem" server with MSTSC.exe?
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#3
Andreas Mariotti Wrote:Maybe something simple like wrong network configuration, name resolution, firewall, authentication, etc.?
Some special configuration on the “problem” servers that is diffrent from the working ones?
Can you connect to the "problem" server with MSTSC.exe?

Cannot connect with mstsc.exe between these 2 servers. Here is another really odd thing: The 2008 server is running hyper-V. The virtual server that runs off this machine (same OS), can connect the the server in question.

The remote server is a client's server, so there is not a lot I can do to troubleshoot that server. As I mentioned, we are able to connect to the remote server from everywhere in our network, except from the one server.
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#4
Sorry I don’t have any Hyper-V experience at the moment
What error message do you receive from MSTSC, only error 516 or some more details?
Can you ping or tracert the target, and can you try “Telnet <Target> 3389” to figure out if the RDP port is listening on the target system.
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#5
I experienced this problem last night.
I could reach some machines, but not others.
Other PC's could reach all machines.
Andreas's suggestion of using TELNET and PING led me to discover the cause of my problem.
TELNET <server> 3389 worked to the working servers but failed to the failing one.
PING could reach both, but I noticed that the working servers returned our internal IP address but the failing ones returned their external IP address. I believe our firewall blocks port 3389 from outside our local network.
I then reviewed the DNS settings on my PC. I had a local (primary) DNS server and a remote (secondary) one which we no longer use. I switched the remote setting to our current remote one and TELNET and visionapp started working again.
I do not yet know the rules being followed for DNS name resolution, but it feels like the system may switch between primary and secondary DNS servers.
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#6
I was getting similar errors accessing virtual 2008 servers on Hyper-V.

You may want to check the windows firewall settings on the server you are trying to RDP into. Windows 2008 and Windows 7 both now have incoming and outgoing firewalls and you need to add an exception for RDP.
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