Re: CuSeeMe 1.0 and Windows 98 II

Jason Williams (streak@ccwf.cc.utexas.edu)
Mon, 29 Jun 1998 20:16:47 -0500 (CDT)


On Mon, 29 Jun 1998, Brian Godette wrote:
> At 04:33 PM 6/29/98 -0600, you wrote:
> >Windows does not let a programmer specify WHICH IP address to bind to.
>
> Ummm, really, guess you better tell that to Microsoft's IIS team, WP, and
> several other companys.

The problem I've seen is applications don't let you DYNAMICALLY choose
which interface to bind to. It's easy to bind to a specific interface
once it's known. That's a problem I had with a little FTP server I wrote
in C for a class. I wonder if this has anything to do with the
gethostbyname() problem with the older Cornell versions.

The only videoconferencing program that I know of that lets you
dynamically choose which interface to bind to is iVisit 2.1b2. They have
an "IP Selector" option which lets you change the bound interface.

> struct sockaddr_in saddr;
> memset(&saddr, 0, sizeof(saddr));
> saddr.sin_family = AF_INET;

Everything up to here is easy enough (though not IPv6 capable).

> saddr.sin_addr.s_addr = bind_ip;

Where does bind_ip come from though? If you use something like
gethostbyname(), you can step thru the address pointers I suppose. But
then again, how do you CHOOSE which one to use? How does a program choose
which bind_ip to use if there are multiple IPs available and they don't
ask the user to choose one? Do they just use the first one? If they use
h_addr in the hostent struct to get the first one, what determines the
order? It seems like it'd be much easier to throw up an option allowing
the user to choose which IP to bind to.

Again, this problem never occured when there was only one numerical IP
address bound to a computer which would be my guess as to why the
programmers never thought much about it. If I understand it right, it's
only a problem because each client also acts as a server..sending AND
receiving data with the IP address embedded within the packets on top of
the IP address in the header.

--
streak@ccwf.cc.utexas.edu    * Jason Williams -- Austin, Tx.  |     |
streak@mail.utexas.edu       * University of Texas at Austin  | ___ |
streak@cs.utexas.edu         * BS Computer Science             \_|_/
*************** http://ccwf.cc.utexas.edu/~streak/ **************|