Thread: Connect to external IP

Hi.
I have made a chatprogram,... which works fine on the newtwork using local IP adresses.

What modifications do i have to do on my code to make it work with external IP adresses`?
(Using Win32API, C++, Winsock)

EDIT: To make my self clearer:
What I want is to make my program usable if the server and client is behind a local router.

Then i must have a bug somehwere.. I have looked everywhere, but i cant find it... ):

I include it if someone really wanna help..

>>Then i must have a bug somehwere
Are you going to give us any kind of clue as to why you think there's a bug? Where do you think the program is going wrong?

well, no. Actually, what is port-forwarding?
If it got anything to do with configuration outside my application, is it something I can do to make my simple chat-server/client program work as easy as the MSN-Messenger?
(No port-forwarding or firewall stuff usualy needed there).

and ONE more question.. If winsock just takes a IP to connect to..
What if 2 computers are behind a local router?
Who of them will then recive the package?(As they have the same external IP)

If not, can I say that: If LAN-testing goes fine, my APP is ready for internet too?

By local router do you mean like a router that does nat for your local network?!

In that case your server can't be part of that nat network, unless you enable "port forwarding" for the server (configure the router to forward to the server's local address and it's port.)

example:
extrenal server's address: 123.1.1.1 --> as known by the world, also the router's address to the world!
local server's address: 192.168.1.1 --> as known only by local network.
listening port: 12345

when you try to connect 123.1.1.1 on port 12345 you're not trying to connect the server, but the router, so this will not work!
if you configure the router to forward all connections for port 12345 to local address 192.168.1.1, you can make server to listen for external connections even if it's local address is not known by any external router in the world!

Originally Posted by Da-Nuka

and ONE more question.. If winsock just takes a IP to connect to..
What if 2 computers are behind a local router?
Who of them will then recive the package?(As they have the same external IP)

and about that one... i suggest you google the word NAT.
the main idea that you have one REAL address that the entire world can reach, and you're using a device, in that case a router to do NAT.
which means: the entire world will see the REAL address of the router, while the router plays with local ports and remembers from which local address came each and every packet, so it will know where to forward the connection to.

And as I said, unless you configure the router to forward by port you can only connect from with in the local LAN to the outside, and NOT from the outside to local LAN.

So...Getting things like portforwarding, router config and firewall config isnt the programmers job?

So if it works fine on LAN/Network, the job is finished, even for internet?

Originally Posted by Da-Nuka

So...Getting things like portforwarding, router config and firewall config isnt the programmers job?

No it is up to the user to decide what he wants to allow past his firewall but if you want your program to configure a firewall/router you could use Microsoft UPnP if the remote firewall/router suports it.

Originally Posted by DA-Nuka

So if it works fine on LAN/Network, the job is finished, even for internet?

Pretty much yes. One difference is that on a LAN there is going to be a lot less latency then on the ineternet, some programs need to be aware of that. For example:

If you want to receive 1024 bytes of data

Code:

recv(TheSocket, Buffer, 1024, 0);

This might work fine on a lan because the data can all arive at once but on the inernet it may not, infact it probably wont.

i disagree on that recv line over there... if you're saying that this will not work then i think you're wrong, it will work only not the entire 1024 bytes will received at once, you will have to call the recv more than once in order to receive the entire 1024.

yes! either that or you can simply use select if you don't know the exact amount of data to receive and also so you will not fall on the exact amount of bytes as you are trying to receive at once with a single recv call.

I don't see what the use of select() has to do with telling how much data is available to be read, other than telling you that there is at least 1 byte (or EOF/error) available.
http://faq.cprogramming.com/cgi-bin/...80608#Mistake3