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Date: Thu, 29 Sep 2005 11:27:10 -0500
From: Brian Ford <Brian DOT Ford AT flightsafety DOT com>
Reply-To: cygwin AT cygwin DOT com
To: cygwin AT cygwin DOT com
Subject: IP_MULTICAST_IF et. all / Winsock[2] value conflict
Message-ID: <Pine.CYG.4.58.0509291103421.2244@PC1163-8460-XP.flightsafety.com>
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I'm having a problem with IP_MULTICAST_IF not working on Cygwin.  While
investigating, I came across this MS KB article that might describe my
problem:

http://support.microsoft.com/default.aspx?scid=kb;en-us;257460

IP_MULTICAST_IF can have two values (2 or 9) depending on whether you're
linking to Winsock 1 or 2.  By preprocessing my source and looking in
/usr/include/cygwin/socket.h, I see we are using the value 2 which means
it will only work if we link to Winsock 1?

IIRC, Cygwin dynamically loads which ever library is present or version 2
if both are available?  I assume we are loading version 2 on my system
given it is WinXP?

I don't understand the Cygwin magic to do this well enough to supply a
patch.  I also don't understand how including Winsock2.h followed by
Ws2tcpip.h is supposed to allow you to link against either library.

Here's hoping that Corinna or someone else is less confused and can supply
a fix to either Cygwin or my limited understanding.  Thanks.

-- 
Brian Ford
Senior Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
the best safety device in any aircraft is a well-trained pilot...

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