Autodial Heuristics

 Last reviewed: December 5, 1997
Article ID: Q164249
The information in this article applies to:
  • Microsoft Windows NT Workstation version 4.0
  • Microsoft Windows NT Server version 4.0

SUMMARY

There are cases when the Autodial feature in Windows NT 4.0 will not be invoked. The following information describes how autodial works with various name resolution procedures.

MORE INFORMATION

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it.

For Winsock applications, Autodial is engaged through gethostbyname() and connect() failures only. This means that pinging an IP address will not invoke Autodial, because a ping sends ICMP packets. However, pinging a DNS hostname such as www.microsoft.com will invoke Autodial. This is because ping calls gethostbyname() to translate the DNS hostname into an IP address.

If you are connected to a LAN locally, Autodial will only engage when an attempt to reach an IP address has failed, and there is already a mapping for the address in the registry for Autodial.

Registry entries for Autodial mappings are located at the following location: 

   HKEY_CURRENT_USER\Software\Microsoft\RAS Autodial\Addresses
If you have booted a using a hardware profile that has no LAN adapter, or you have no LAN adapter, Autodial will engage regardless of whether the address is in its database or not.

Each entry under the \Addresses key includes a Network value, which corresponds with one RAS connectoid (such as 'NETWORK0') under the following Registry key: 

   HKEY_CURRENT_USER\Software\Microsoft\RAS Autodial\Networks
This Network value enables Autodial to know which RAS connection to dial to connect to the specified server.

The registry also holds a database for addresses it will ignore. The entries are located at: 

   HKEY_CURRENT_USER\Software\Microsoft\RAS Autodial
   \Control\DisabledAddresses

   NOTE: The above registry key is one path; it has been wrapped for
   readability.
There are two types of address aliasing that Autodial applies when determining which RAS phonebook entry to dial:
  • Domain name aliasing: <name1>.microsoft.com is equivalent to <name2>.microsoft.com or any other hostname of the form *.microsoft.com.
  • WWW aliasing: www.microsoft.com is equivalent to www.netscape.com or any other hostname of the form 'www.*'.

This means that if the original address is not found in the database, then the aliasing rules are applied in attempt to find a suitable RAS phonebook entry. 
Keywords          : NTRAS NTSrvWkst nttcp kbnetwork
Version           : WinNT:4.0
Platform          : winnt
Issue type        : kbinfo

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Last reviewed: December 5, 1997
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