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Re: NAT-PMP Broadcast Address?
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Re: NAT-PMP Broadcast Address?


  • Subject: Re: NAT-PMP Broadcast Address?
  • From: Josh Graessley <email@hidden>
  • Date: Wed, 12 Sep 2007 12:54:58 -0700


On Sep 12, 2007, at 12:00 PM, email@hidden wrote:

On Sep 11, 2007, at 12:02 PM, Josh Graessley wrote:

Ya I will listen for changes, maybe with just the notifications that happen in the spec though. Also, I think I found a flaw in NAT-PMP...because you can't query what ports your machine opened? I want to be able to check a port and see what it is. But the only way to do that is to basically try to remove the port. You will get an error code if another machine is using the port. However, if your computer had a port allocated, you just get an answer that you successfully either got the port, or changed its timeout, which for removal is a timeout of 0. There doesn't seem to be a way to determine if the port was already open. I realize that is how the spec is designed to work, so that multiple requests return multiple success replies, but this still seems to be a pretty major thing to overlook.

This is by design. Do your own book keeping :) If you need a mapping, create it. Renew it periodically as a DHCP lease would be renewed (about half way through). When you're done with it, dispose of it.

I actually agree with this, because normally there is no need to spy on your neighbors, so it makes sense for each machine to do its own thing. However, I want to be able to bring up some kind of dialog like "Sorry, port 1234 is in use by 192.168.0.2" or whatever, so people can tell their buddies to stop hogging the port. I will just say the port is in use by another machine.

NAT-PMP is intended to be used in conjunction with a service that discovers address/port pairs. Whether this is some third party server that keeps track of people looking to play a game together or something like wide area bonjour, the port number is arbitrary. If you want to map the local port 80 to the global port 80 and the global port 80 is in use, NAT-PMP will happily give you back some other port instead. As long as someone is using another service to discover the port instead of just assuming it's 80, you're fine. You have to discover the address somehow. The port is really just another another piece of information you have to discover along with the address.


-josh
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References: 
 >NAT-PMP Broadcast Address? (From: email@hidden)
 >Re: NAT-PMP Broadcast Address? (From: Matt Slot <email@hidden>)
 >Re: NAT-PMP Broadcast Address? (From: email@hidden)

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