Applications Calling GetHostByName() for the Local Host Name May See the List of IP Addresses In an Order that Does Not Match the Binding Order.

ID: Q164023

The information in this article applies to:

Microsoft Windows NT Workstation version 4.0
Microsoft Windows NT Server version 4.0
Microsoft Windows NT Server version 4.0, Terminal Server Edition

SYMPTOMS

When a Windows Sockets application calls gethostbyname() to resolve the local hostname to a list of IP addresses on a multihomed computer, the list may be returned in an order that does not match the binding order displayed in Control Panel, or the order that IP addresses were assigned to network interface cards (NICs).

CAUSE

Changes made to support Windows Sockets 2 produced this behavior.

RESOLUTION

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, please see the following article in the Microsoft Knowledge Base:

Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack

When the new fix is applied, and gethostbyname() is used to resolve the local hostname on a multihomed computer, the list of IP addresses will be returned in the following order:

The first address from each NIC in the system. You can see the order in which they will appear by clicking the Bindings tab in the Control Panel Network tool.

The remainder of the IP addresses from each NIC. You can see the order in which they will appear by clicking the Bindings tab in the Control Panel Network tool.

Additional addresses, such as those dynmically assumed by a cluster server.

So if you had a computer similar to the following:

Card A - Addresses 1,2,3
Card B - Addresses 4,5,6

The order returned would be 1,4,2,3,5,6. That is, the first address from each NIC (1,4) and then the remainder from each NIC (2,3,5,6).

STATUS

Microsoft has confirmed this to be a problem in Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition. This problem was first corrected in Windows NT 4.0 Service Pack 4.0 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4.

MORE INFORMATION

For additional information about this issue, please see the following article in the Microsoft Knowledge Base:

ARTICLE-ID: Q171320
TITLE : How to Change the IP Address List Order Returned

To Change the order that addresses are returned:

1. Open Network Control Panel

2. Choose the bindings tab

3. Choose all protocols in the Show Bindings for drop down box

4. Expand the TCP/IP protocol

5. Addresses are tied to the specific Network Card. Move the NICs up or down the list to get the desired order.

Use ipconfig /all at the command line to assist in correctly identifying the NICs.

RAS interfaces will appear as NDISWANx . The addresses that RAS servers and RAS clients use are also returned in the list. This can have some adverse effects on applications that are not written to try other addresses when the first returned address fails.

Additional query words: ping gethostbyname localhost multihomed multi-homed


Keywords          : kbnetwork NT4SP4Fix kbbug4.00 nttcp kbfix4.00.sp4 NTSrvWkst 
Version           : winnt:4.0
Platform          : winnt 
Issue type        : kbbug

Last Reviewed: April 10, 1999