Microsoft KB Archive/250603

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Knowledge Base

ICS May Not Function Properly with DNS or DHCP Server Services on the Same Computer

Article ID: 250603

Article Last Modified on 2/28/2007


  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows 2000 Datacenter Server

This article was previously published under Q250603


When you have a server running Dynamic Host Configuration Protocol (DHCP) or Dynamic DNS (DDNS), the Internet Connection Sharing (ICS) service may not function correctly or may cause some services to stop working. In addition, various error messages may be displayed.


The ICS service is one implementation of Network Address Translation (NAT) that Windows 2000 uses. The ICS service automatically sets up a mini DHCP scope and a DNS Proxy service to enable clients on the private network to use ICS and get on the Internet.

The DHCP allocator and DNS Proxy services are not configurable in ICS and start as soon as the service is enabled. Because these services bind to the same TCP ports that a DDNS or DHCP server uses, ICS conflicts if these services are running.


To resolve this issue, do not run the ICS service on a DHCP or DDNS server. NAT (which is installed using routing protocols in the Routing and Remote Access Service (RRAS) snap-in) works correctly if you do not enable the DNS Proxy service or the DHCP allocator.


Microsoft has confirmed this to be a problem in Microsoft Windows 2000.


For more information about how to implement NAT, refer to the Windows 2000 Help file.

To setup NAT to NOT use the DHCP allocator, do not check the box for "Automatically assign IP addresss using DHCP" on the Address Assignment tab of NAT properties.

To setup NAT to NOT use the DNS Proxy Service, do not check the box for "Clients using Domain Naming System (DNS)" on the Name Resolution tab of NAT properties.

Additional query words: fail fails

Keywords: kbbug kbnetwork kbpending KB250603