Re: How can I make the server to call back to client without being blocked by firewall.
From: jeff Lee (jeff-lee@attbi.com)Date: 10/01/02
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From: "jeff Lee" <jeff-lee@attbi.com> Date: Tue, 01 Oct 2002 00:45:05 GMT
Thanks David.
Since there are tons of commercial applications available,
how can we pick a port which is guaranteed to be usable?
Regards,
Jeff
For the following 2 reason
"David Schwartz" <davids@webmaster.com> wrote in message
news:3D982505.2C9DE7C2@webmaster.com...
> Bernie M wrote:
>
> > > Our application will have thousands of clients, and any one of them
can
> > > make
> > > connection to any one of others via our server. Therefore, our server
has
> > > to somehow do a call back to tell the called client that somebody is
> > > trying
> > > to
> > > reach him. I am sure we will hit fire wall when our server tries to
open a
> > > connection
> > > to the client.
> > >
> > > We don't want to slack the client's fire wall at all, so I am thinking
> > > an always on TCP connections from the clients to our server may solve
the
> > > problem.
> > > Anyway all the clients have to log in before they can make a call or
be
> > > called.
> > >
> > > Do you think this will work?
>
> All you have to do to make an application firewall friendly is the
> following:
>
> 1) If you prefer to use UDP, offer an option to fallback to TCP as
> well.
>
> 2) Make sure any client software you develop permits a proxy to be
> configured.
>
> 3) Document exactly what ports you use and what types of connections
> you use.
>
> 4) Provide a mode that requires the client to only make outbound TCP
> connections.
>
> This will allow anyone who wants to use your application to properly
> configure their firewalls and clients. Do not ever attempt to evade or
> bypass firewalls by using provisions intended for one protocol to
> smuggle through another. This will just result in reputable firms
> blacklisting your application.
>
> DS
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