Opening/verifying UDP port

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Opening/verifying UDP port

Right, I've been looking into this for quite a bit now and I'm totally lost. I need to open a specific udp port or verify that it has been opened by the application firewall (let's call it port X). The situation:

I've added the application to the firewall and allowed incoming connections
When I start up the network server inside the app, the firewall log shows the app is listening on port X with proto=6 (I assume 6 is TCP, couldn't find a list of these numbers on the web)
Some of the network functionality works and I can verify the inbound TCP connection on port X using telnet and the console inside the app
Remote clients aren't able to connect to my server suggesting there's a problem with UDP on the same port. Both TCP and UDP on port X are required for remote clients
Both TCP and UDP for port X have been forwarded on the router

I tried to connect to the UDP port using nc, but as nc always indicates a successful connection when using UDP and as I don't know the application's own protocol/packet system, I can't get any response from the server to indicate that it is actually accessible.

There are a lot of suggestions on the web to use ipfw, but by default the only rule in ipfw is to allow all connections so it wouldn't interfere with the application firewall so that's no use.

I do like the application firewall idea, but once again I find that by trying to make things more user friendly, Apple has broken some of the functionality by removing the good old option of doing things manually. So if anyone has any ideas, all help is most welcome.

MacBook Pro 15, Mac OS X (10.7.2)

Posted on Jan 19, 2012 3:00 AM

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Answer 1

Barney-15E

Level 10

112,518 points

Jan 19, 2012 4:37 AM in response to johankytt

There are a lot of suggestions on the web to use ipfw, but by default the only rule in ipfw is to allow all connections so it wouldn't interfere with the application firewall so that's no use.

The application firewall and ipfw can coexist. And, ipfw seems to take precedence if there is a confict. So, if the application firewall is not opening the UDP port, then open it with ipfw. That may at least give you an indication if the application firewall is the problem. See http://support.apple.com/kb/ht1810

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Answer 2

johankytt Author

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Jan 19, 2012 5:11 AM in response to Barney-15E

But as I said before, by default the only rule in ipfw is to allow all traffic:

65535 allow ip from any to any

So it would make no sense to add another rule to specifically allow that udp port. Or would it?

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Answer 3

Linc Davis

Level 10

209,541 points

Jan 19, 2012 6:27 AM in response to johankytt

Does your app work with the application firewall (which you don't need) turned off?

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Answer 4

Barney-15E

Level 10

112,518 points

Jan 19, 2012 3:21 PM in response to johankytt

johankytt wrote:

But as I said before, by default the only rule in ipfw is to allow all traffic:

65535 allow ip from any to any

So it would make no sense to add another rule to specifically allow that udp port. Or would it?

Yes, because the application firewall is blocking access to that port, at least in theory. Linc has a better troubleshooting technique, though.

If your theory that ipfw leaves everything open, then the application firewall couldn't possibly be blocking anything at all.

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Answer 5

Linc Davis

Level 10

209,541 points

Jan 19, 2012 3:27 PM in response to Barney-15E

The application firewall doesn't block any port. It blocks incoming connections at the application level, not at the transport level.

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Answer 6

johankytt Author

Level 1

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Jan 27, 2012 2:19 PM in response to Linc Davis

Right, the problem is becoming more and more mysterious. It is definitely not the firewall on my laptop that's the issue. The remote client gets the same symptoms when I've got the firewall turned off. I've had a hint that it might still be a TCP not UDP port issue. But anyway, now my laptop has been eliminated from the list of suspects so this topic can be closed and left unanswered as the original answer is not needed anymore. Thanks for the help 🙂

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Answer 7

satcomer

Level 4

1,539 points

Jan 28, 2012 12:14 AM in response to johankytt

Read the article Getting port mappings and DHCP usage from an Airport Device .

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Answer 8

Aug 9, 2012 1:55 PM in response to satcomer

I'm lost,

I'm trying to open port 16000 for UDP only, do I put in my default gateway address or the ip4 address or my 68.xxx address?

Also, how do I open DMZ?

Airport Uility 7.6.1

airport extreme 2nd gen

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Answer 9

Aug 9, 2012 2:34 PM in response to Fairwayman1960

On the bottom slide do I put anything in the default host field that is blank?

Took these screen shots trying to display what I mean. I did ipconfig and I see default gtway ip...ip4 ip

and subnet ip, which ip address do I put in the private ip field? 10.0.1.201 was in there when I brought up this screen. I have read the port mapping tips but still do not understand. Please help!

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Answer 10

Aug 11, 2012 12:20 PM in response to Fairwayman1960

I would really appreciate some help with this situation, thanks in advance.

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