Resolving conflict: Http ports and XPSP2

A giant leap forward in Windows HTTP technologies was introduced with Windows Server 2003, namely http.sys. Http.sys includes a kernel-mode listener that can dispatch to any process on the machine. This was great news to those of us that wanted to share port 80 with other applications (IIS for example). It also has a comprehensive namespace security mechanism which admins can use to delegate sections of the global hierarchical directory space to less-privileged accounts. IIS 6.0 (which shipped with Server 2003) was built on top of http.sys and so did not require exclusive access to its configured port #s.

Indigo’s standalone HTTP IChannelListeners are built on top of http.sys. That means that if you are not hosted in IIS, your process will need to have access to any http addresses that your ServiceHost is configured with. If the process is not running as admin you will need to add a reservation using httpcfg.exe. Alternatively, you can call the HTTP configuration APIs, such as HttpSetServiceConfiguration, directly.

There is one more wrinkle when working on XPSP2. While http.sys was backported to XP as part of Service Pack 2 (yay), IIS 6.0 was not (boo). This means that if you have IIS running on your XP box, then you are using IIS 5.1 which is built on top of a listening socket and thus owns port 80. If you try to open a Service using port 80 while IIS is running you will get the following error:

AddressAlreadyInUseException: HTTP could not register URL http://+:80/myService/ because TCP port 80 is being used by another application.

You have 2 choices to remedy this situation:

  1. Stop IIS (using “net stop w3svc”)
  2. Setup your service to use a different port#

Setting up a different port# is usually a simple matter of changing your Service’s URL. However, a more subtle variation of this failure occurs for clients that use WsDualHttpBinding (or a custom binding with CompositeDuplexBindingElement and HttpTransportBindingElement). Your indication here is the inclusion of “Temporary_Indigo_Addresses” as in:

AddressAlreadyInUseException: HTTP could not register URL http://+:80/Temporary_Listen_Addresses/51E705D5-E7B5-472B-B6B9-A6A60FE93B7A/ because TCP port 80 is being used by another application.

When your client is using a Dual binding, then the system creates a temporary address to listen on, in order to establish two-way communication over two one-way channels. For HTTP, this address by default is setup on a subtree of http://+:80/Temporary_Indigo_Addresses. This has the advantage of being a namespace pre-ACLed by Indigo for access by all processes. You can override this default through the ClientBaseAddress property on WsDualHttpBinding and CompositeDuplexBindingElement. You can do this either through code:

binding.ClientBaseAddress = "http://localhost:8000/myClient/"

or config:

<wsDualHttpBinding clientBaseAddress="http://localhost:8000/myClient/"/>

Good luck on future port conflict avoidance!

28 thoughts on “Resolving conflict: Http ports and XPSP2

  1. Ephrem

    Hi I had the

    AddressAlreadyInUseException: HTTP could not register URL http://+:80/Temporary_Listen_Addresses/51E705D5-E7B5-472B-B6B9-A6A60FE93B7A/ because TCP port 80 is being used by another application.

    Problem and Your solution guded me the right way. However there is one little problem on your suggested solution.

    when the clientBaseAddress is specifyed the address should directly refer to the client Machine menaing can not be stated as localhost or the connection will time out.


    you set cant clientBaseAddress=http://localhost:8000/client/,
    it Should be http://clientmachinename:8000/client

    Thank you again for the Help

  2. Kenny

    Yes, localhost was used as an example for when you are accessing a service on the same machine. if you are doing cross-machine communication then you need to use a resolvable address (i.e. your client machine name for example)

  3. Kenny

    You can have your deployment app (which installs/generates the client configuration file) detect the client machine name, yes?

  4. Martin Naughton

    Thanks Kenny – that helped out greatly.

    A couple of additional notes, related to my experience.

    1) I found that, if the service is already using a non-standard port, the client should use a different non-standard port (e.g. Service uses port 666, Client uses port 667). This may be obvious to some.

    2) Anti Virus programs may complain if non-standard ports are used. Mine did, so I had to add the two applications to the permitted list of executable files.

  5. Darshan

    Does this mean that i could have a self hosted WCF service share port 80 with IIS? If so, how do i go about sharing the port?

  6. Sunil

    Really good help Kenny but i have one problem
    I have override ClientBaseAddress property on WsDualHttpBinding like


    Now it gives me this error:

    HTTP could not register URL http:// :1045/WCFTest.Host/ because TCP port 1045 is being used by another application

    what should i do? please help me.

    ***********This is my configuration code **************************

  7. Kenny

    Darshan, you can share port 80 with IIS if you are using 2k3 server or later (that is, IIS 6.0 and later). IIS 5.1 (on XP) does not use http.sys and there for you cannot share port 80 with IIS on XP.

    Sunil, it sounds like an application already has 1045 open. You can use “netstat -a” to see which process has 1045 in LISTENING mode.

  8. Peter

    when You say that we have to “use resolvable address (i.e. your client machine name for example)”
    You mean that client computer has to be ‘visible’ from server?

    by ‘visible’ I mean that you can ping client computer from server by it’s name

    in my app.config I have clientBaseAddress=”http://client_machine_name:8000/myClient/”
    but I still get timeouts…

    please help…

  9. Venemo

    This is great, but how do I detect the client’s machine name from .NET? And there is one more thing: if I specify a clientBaseAddress and run more than one instances of the client application, it will also throw this exception, because the other instance of the client already uses that particular port.

  10. Ken

    I am just now delving into WCF and I am trying to reolve the latter error you described for IIS 5.1 running on XP. I have attempted to emulate your solution but I still get the same error – below is my configuration file – can you please help? Thanks!

  11. Ken

    I have a Windows 2003 Server and I deployed the service to that server such that the reference is now instead of localhost. I also chnaged the clientBaseAddress to and I am still getting the same error – any ideas?
    BTW – THe WSDL looks fine and I can obtain it without any problems through a browser.

  12. Godwin

    How do I use port 80 for communication for dual http binding?

    I wan’t to create something like a HTTP tunnel through which I can accomplish two way communication.


  13. echoe

    Sirs, my conclusions on WCF:

    * In WCF, if you need bidirectional communication, you have two options: netTcpBinding and wsDualHttpBinding.
    * netTcpBinding may not work behind firewalls, it depends on your client’s security policies.
    * If your client lives behind network Proxy (i.e. squid), you cannot use netTcpBinding.
    * But guess what? wsDualHttpBinding is Proxy enabled, great!

    …ejem, no… If your client is in a private network behind a proxy, something very common, the server will never be able to see the client: that’s the idea of a proxy firewall my friends. That’s what you may be suffering, no? based on what I read from some posts here.

    Conclusion: wsDualHttpBinding is completely USELESS and netTcpBinding is almost as USELESS, while being impossible for any of them to work behind a network Proxy.

    Microsoft, com’on? Don’t you have the resources to solve that? Do you think we will adventure in WCF just to do either LAN applications or web sites?

  14. Santhosh

    Sir I have a windows application running which starts WCF service. Another windows application has to interact with the WCF service. Now my error is

    The remote server returned an unexpected response: (407) Proxy Authentication Required ( The ISA Server requires authorization to fulfill the request. Access to the Web Proxy service is denied. )

    In local system it works fine but in remote application it is not working.

    Please help me in this problem.

  15. Kenny

    Santhosh, it sounds like you need to setup proxy authentication on your binding.
    Huong, Environment.MachineName will help you out

  16. Kenny

    echoe, let me provide some counterpoint here.
    1) NetTcpBinding is intended to be used within a corporation/network (i.e. intranet). For most internet-based communication you need to use HTTP as that’s what’s widely deployed and supported through proxies, etc. NetTcp was never intended to replace all uses of TCP
    2) WsHttpDualBinding was intended for scenarios where both sides are globally addressable (such as B2B communication). It was not intended to address NAT traversal.

    For what you are desiring (i.e. bidrectional communication behind a NAT/firewall), you’ll want something like the HTTP polling duplex channel that’s shipped in Silverlight. It uses a client-based HTTP polling mechanism to allow bidirectional communication to occur even though it’s always “initiated” by the client from the HTTP perspective.

  17. Kenny

    Godwin, if you want to use port 80 on XPSP2 then you need to disable IIS or change the port that it’s using.

  18. Karyn

    Hi Kenny

    on your last comment you say “if you want to use port 80 on XPSP2 then you need to disable IIS or change the port that it’s using.” i am very low on knowledge about ports and IIS etc.

    Can you explain this in dummy form. I cant disable IIS as i need it for other things, so do i change the port IIS is running on or the port that the service runs on and if the latter how do i do this (I have tried the former but it doesnt appear to make any difference) ?



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