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> Multiple messengers on same network
kompion
post Apr 7 2009, 06:37 PM
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Hi, I'm sure this questions must have been asked before but I can't find the answer anywhere.

Two people have just moved in with me so now we're all using WLM behind the same router. As yet I haven't set up any port forwarding for messenger as I gather that would prevent them from logging in. Is there any chance that messages/video or audio calls might get sent to the wrong computer?

If more than one of us was logged into WLM how does the router know which internal IP is associated with each messenger account? I can see how it would work if my computer sends out a request and it is answered, but if it's just an inbound request, like when someone starts a conversation with one of us, then will it always find its destination?

Hope I don't seem paranoid, but I'd like to be reassured that messages or calls aren't getting lost or, worse, accessible to others.

Thanks for any help.
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Lord d'Eath
post Apr 9 2009, 07:50 AM
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QUOTE (kompion @ Apr 7 2009, 07:37 PM) *
Hi, I'm sure this questions must have been asked before but I can't find the answer anywhere.

Not as far as I know msn_happy.gif

QUOTE (kompion @ Apr 7 2009, 07:37 PM) *
As yet I haven't set up any port forwarding for messenger as I gather that would prevent them from logging in.

That would depend on which ports you forwarded. WLM hasn't officially used specific ports for a long time (see also my announcement), and instead uses UPnP to forward ports dynamically as and when they are needed. I think that you would have to specifically forward *all* (1-65535) ports to stop them logging in, and even then it might not - that would depend on your router's implementation, I think. I have once broken all Internet access to everyone else behind my router by forwarding all ports, but forwarding the ports that are traditionally used by WLM hasn't ever broken anything.

QUOTE (kompion @ Apr 7 2009, 07:37 PM) *
Is there any chance that messages/video or audio calls might get sent to the wrong computer?

Absolutely no chance at all, as I explain below.

QUOTE (kompion @ Apr 7 2009, 07:37 PM) *
If more than one of us was logged into WLM how does the router know which internal IP is associated with each messenger account?

Through the magic of NAT! I won't go into details, but you can research NAT (Network Address Translation) yourself if you want to. Basically, once one machine initiates a connection to a given IP address on a given port, the router remembers that that connection exists and its details, then forwards packets matching that IP address & port to the internal machine that first initiated the connection.

QUOTE (kompion @ Apr 7 2009, 07:37 PM) *
I can see how it would work if my computer sends out a request and it is answered, but if it's just an inbound request, like when someone starts a conversation with one of us, then will it always find its destination?

Even inbound requests are internally achieved as an outbound request. Messenger keeps one TCP connection open to the "notification" server, and that connection is where the WLM network sends details of contacts logging on, changing their names, etc.. That same connection is also used when a new conversation is started: the notification server sends a message to your WLM client saying that there's a new conversation starting, and your client then initiates a connection to a new server to handle the conversation. At no point do the Messenger servers initiate connections to your computer.

With file transfers, voice chat and webcam, it's a slightly different situation. The request/notification will go through the existing conversation connection. The two clients will then negotiate how to connect to each other. If one side is publically accessible (either having all the necessary ports forwarded or being directly connected to the 'net), that side can listen for a connection initiated by the other side. If both sides are behind NAT, however, they will have to try and use UPnP to forward a port temporarily. If one side successfully uses UPnP to do that, that side can listen for incoming connections, just like it could if it was publically accessible already. If neither side can use UPnP to make itself visible, problems occur. With a file transfer, the file will go via the Messenger servers as hidden "messages" (because we already know that we can connect to the Messenger servers and that messages can get through). I'm pretty sure that voice chat and webcam can't go through the Messenger servers, though.

So basically you just need UPnP on your router and computers. Most modern routers have UPnP available. Whether it's enabled by default is something you'll have to find out; enable it if it isn't. The aforementioned announcement topic gives details on enabling UPnP for Messenger in Windows, though I'm not sure I ever updated it for Vista.

(Disclaimer: a fair amount of the above could well have changed since I last played with the WLM protocol. I suspect that most of the fundamentals are the same, though. Also, that paragraph about how file transfers etc. work is largely guesswork on my part, but it's logical guesswork and it matches my observations.)
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