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Using UDP or TCP messages through firewalls

Posted on 2004-09-17
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Hi

I am not an expert under UDP or TCP and i am currently working on the possiblity to make an applicatoin.

The application will be composed by two executable.
One on a client machine and another on a server.
The both machines have to communicate some specific data thourgh an UDP or TCP port.

The problem is that the machines can be separated by one or several firewalls.

The other problem is that we need to make a plug and play application with no needs to the client to configure anything.

So is there any way to make UDP/TCP communications through firewals in such a case ?

Thanks
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Question by:eric3333
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by:SunBow
SunBow earned 250 total points
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> So is there any way to make UDP/TCP communications through firewalls in such a case ?

Firewalls typically have nothing to do with either UDP or TCP, they are IP.  THey can filter the dotted address and some by port (blocking or allowing).

What you need is to go as close to standard as possible for communicating on addresses with ports no matter what your traffic is, for example, if doing your own eMail service consider using the eMail ports such as for SMTP 25.

Some may filter all traffic, so another thing to place at head of checklist is to investigate the firewalls themselves, ask their administrators which ports are acceptable and which are not for the purpose you have in mind. Never use ports that are not approved of.  Their staff may even have a fixed list of ports for you to select from, to properly identify and route traffic.  

Note that whether you select UDP or TCP is not the issue.  If you have the leverage, you might want to consider simply using FTP to perform the communication.  Send the information from one computer to the other in the form of a file. There are standard protocols and port for doing that, why reinvent the whell when unnecessary? But your needs may differ.
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ahoffmann earned 250 total points
ID: 12090910
> So is there any way to make UDP/TCP communications through firewals in such a case ?
the firewall has to be configured to allow UDP or TCP on that port.

Or you may tunnel your protocol, for example using ssh (port 22)
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by:eric3333
ID: 12100888
A question

If i use FTP with standard port can it be possible that i will go through firewalls ?

If yes what is the interest of firewalls in this case ?

Thanks
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by:ahoffmann
ID: 12101415
firewalls are able to allow ftp, most only allow active ftp protocol
the interest is to block anything else than what is allowed ;-)
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by:eric3333
ID: 12101955
Thanks a lot
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