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Date: Thu, 29 Sep 2005 12:04:34 -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: Re: IP_MULTICAST_IF et. all / Winsock[2] value conflict
In-Reply-To: <20050929165053.GU12256@calimero.vinschen.de>
Message-ID: <Pine.CYG.4.58.0509291152490.2244@PC1163-8460-XP.flightsafety.com>
References: <Pine DOT CYG DOT 4 DOT 58 DOT 0509291103421 DOT 2244 AT PC1163-8460-XP DOT flightsafety DOT com>  <20050929165053 DOT GU12256 AT calimero DOT vinschen DOT de>
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On Thu, 29 Sep 2005, Corinna Vinschen wrote:

> On Sep 29 11:27, Brian Ford wrote:
> > 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.
>
> There's no easy fix right now.  We have to drop all traces of Winsock1
> in Cygwin and change the headers accordingly.

Can't we just translate these based on a flag indicating what version we
dynamically loaded?

> Since you didn't say what problem you had, I assume that IP_MULTICAST_IF
> just didn't do what you wanted.

Correct.  It did not send out the interface I requested.

> Did you try to use just the value 9 instead of IP_MULTICAST_IF?

Not yet, but I will this afternoon.  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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