Microsoft KB Archive/192564

= INFO: Set Winsock Control RemoteHost and RemotePort for UDP =

Article ID: 192564

Article Last Modified on 11/18/2003

-

APPLIES TO


 * Microsoft Visual Basic 5.0 Learning Edition
 * Microsoft Visual Basic 5.0 Professional Edition
 * Microsoft Visual Basic 5.0 Enterprise Edition

-



This article was previously published under Q192564



SUMMARY
When a UDP message is received by a Winsock control, the RemoteHostIP property is set to the IP address of the remote machine, and the RemotePort property is set to the IP port of the remote UDP application. The previous properties values are overwritten.

This could create a problem if the user was not expecting data on that port from a different RemoteHostIP. Attempts to call the SendData method without setting these two properties to the appropriate values might send the data to an unplanned recipient.

Whenever a UDP socket is being used, you should always reset the RemoteHostIP and RemotePort properties to your own known values before calling the SendData method.



MORE INFORMATION
This is by design. At the Winsock layer, the sendto API requires a sockaddr structure of the remote UDP peer to send the message to, and the recvfrom API always gets a sockaddr structure for the remote UDP peer. The Winsock control internally uses the same sockaddr structure in both sendto and recvfrom API. As UDP is a connectionless protocol, it is possible that one UDP peer could receive a UDP message from a third machine unexpectedly. Therefore, it is important to reset the RemoteHostIP and RemotePort properties to your own known values before calling the SendData method.

Additional query words: kbVBp500 kbCtrl kbNetGrp kbNetwork kbWinsock kbNTOS400 kbWinOS95 kbWinOS98 kbAPI kbdss kbDSupport kbVBp

Keywords: kbinfo KB192564

-

[mailto:TECHNET@MICROSOFT.COM Send feedback to Microsoft]

© Microsoft Corporation. All rights reserved.