DOCUMENT:Q192564  11-SEP-1998  [vbwin]
TITLE   :INFO: Set Winsock Control RemoteHost and RemotePort for UDP
PRODUCT :Microsoft Visual Basic for Windows
PROD/VER:WINDOWS:5.0
OPER/SYS:WINDOWS
KEYWORDS:

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The information in this article applies to:

 - Microsoft Visual Basic Standard, Professional, and Enterprise Editions,
   32-bit only, for Windows, version 5.0
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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
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Version           : WINDOWS:5.0
Platform          : WINDOWS
Issue type        : kbinfo

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