|
Posted by imhotep on October 3, 2006, 1:28 am
If you were Registered and logged in, you could reply and use other advanced thread options
>
>>
>>>I am trying to write a freeware client/server program that needs to scan
>>>the server's ports for the server's open UDP port.
>>>
>>> Before I get too deep into this, are there any problems that I need to
>>> know of if I send a probe UDP packet that looks for the server to all
>>> ports on at the server's target IP?
>>
>> Send one UDP packet to scan all ports? I'm not sure this is possible the
>> way you have described it.
>
> What I meant was that the server (behind NAT1) will be expecting an
> encrypted value from the client (behind NAT2).
>
> I would send this same encrypted info to all UDP ports on the server's
> known
> external IP to get a valid connection to the server. Of couse this would
> mean sending a packet for each possible port, but the packet contents
> would all be the same.
Are you trying to do this to find the "secret" port???
> Sorry for the confusion.
>
>>> The reason I am asking is that some users of this freeware server will
>>> be behind NATs and I may have to probe for the external port assigned to
>>> the
>>> internal server by the NAT device. The client would send an encrypted
>>> string that the server would know how to respond to. If this encrypted
>>> value is not what the server expected, no communication would take
>>> place.
>>
>> Most client/server apps more typically will require you to either
>> manually configure the NAT firewall so that it will work, or know how the
>> NAT is configured and manually configure the client and server so it will
>> work. Most client/server apps also more typically have a standard port
>> number for the server that is recommended to be configured as a static
>> port number in NAT.
>>
>> How is the NAT set up?
>
> I will not know. Neither may the server operator. Think of it as a P2P
> app using UDP behind NATs.
>
>>Are you sure the server's port will change to an unknown value during the
>>NAT?
>
> I don't want the end user to have to configure firewalls or NATs. I want
> this to be as simple as possible for them.
>
> Being behind a NAT (and not setting up any manual port forwarding) means
> that the NAT will choose an unused port at random for outbound UDP
> connections (just like it does for HTTP connections when you surf the
> web).
Correct...
> So, the external port for the server will be unknown.
It will be dynamic...
>>How is it that the NAT port being used is not already known?
>
> See above.
>
>>I would expect the client's source port to change dynamically, but the
>>server's destination port to be known by whoever configured the NAT.
>
> I am really trying to make this as simple as possible by not requiring the
> end users to set ports in their NAT or Firewall. Also, some people may
> want to use the software but not have access to the NAT or Firewall to
> make manual changes.
Honestly, I think you will need a server in the middle. For example,
Client-A connects Internet-Server-A then Client-B connects to
Internet-Server-A, Next, they can use the Internet-Server-A as a kind of
packet proxy (for lack of a better techie word)...
This would allow you to not force any users to reconfigure their NAT
Routers, etc and would be seemless...
Just a thought...
Imhotep
| 
XML site map