Author Topic: UDP is open but TCP isn't  (Read 47057 times)

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Offline Shae49

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UDP is open but TCP isn't
« on: June 01, 2016, 07:30:11 PM »
There is a great chance I am being oblivious as I am quite a newb to all of this, so TIA. Recently I have been trying to forward the port 25565 so I can set up a Minecraft server to play with my friends, but for some reason my TCP is supposedly closed while my UDP is open. I used PFPortChecker to test this. I have allowed the ports through Windows Firewall, I have disabled my anti-virus's firewall, and I have tried to port forward several times. 99% sure I have done everything correctly including making my IP static, but there is always that 1%. Any help would be greatly appreciated!

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UDP is open but TCP isn't
« on: June 01, 2016, 07:30:11 PM »

Offline trpted

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Re: UDP is open but TCP isn't
« Reply #1 on: June 02, 2016, 01:12:28 PM »
#1 From DSLR ( -> Forums -> Broadband and Networking -> Networking -> How to know if ports are reaching my computer from outside the post by DSLR user mackey (user # 1479488) on 2015-Sep-24 at 8:05 pm - if you wanted to test port 5154, besides using an inbound client side port checker:

Run tcpdump (`tcpdump -p -n -i <interface> port 5154` would be a good command to start with). If you see incoming TCP SYN packets (not SYN/ACK), or incoming UDP packets from an IP which did not have an outgoing packet first, then the port is open.

#2 For tcpdump on Windows I found this info

#3 For a TCP and a UDP port checker you can use

#4 Using a packet sniffer (like tcpdump = command line / like wireshark = GUI) you should see the traffic from an outside IP address reaching your computer, like I did (when you are forwarding the ports to your computer).

Code: [Select]
user-name@pc-name:~$ tcpdump -p -n -i eth0 port 5154
tcpdump: eth0: You don't have permission to capture on that device
(socket: Operation not permitted)
user-name@pc-name:~$ sudo tcpdump -p -n -i eth0 port 5154
[sudo] password for user-name:
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
08:40:24.169428 IP > UDP, length 6
08:42:15.839461 IP > Flags [S], seq 1464127243, win 8192, options [mss 1460], length 0
08:49:05.773987 IP > UDP, length 0
08:49:06.938818 IP > UDP, length 0
08:57:57.580814 IP > Flags [S], seq 3027635480, win 14600, options [mss 1460,sackOK,TS val 4240686068 ecr 0,nop,wscale 8], length 0
08:57:57.712334 IP > Flags [S], seq 1267700791, win 14600, options [mss 1460,sackOK,TS val 4240686102 ecr 0,nop,wscale 8], length 0
08:57:57.840328 IP > Flags [S], seq 1515263633, win 14600, options [mss 1460,sackOK,TS val 4240686134 ecr 0,nop,wscale 8], length 0
7 packets captured
7 packets received by filter
0 packets dropped by kernel

#5 Some notes about my testing..

a) is from this same computer.

b) As noted at -> Services -> Shield's Up they own -thru-

c) I believe is from as it only checks TCP ports.

d) As you can see, I checked port 5154.

#6 The only UDP ports that checks, that I know of, are:

a) DNS (53) -> Freeware -> Utilities -> DNS Benchmark -> DNS Spoofability Test Introduction (or -> Services -> DNS Spoofability Test)

b) Universal Plug n'Play (UPnP) =  1900

From -> Services -> Shield's Up: Click on Proceed and then GRC's Instant UPnP Exposure Test.
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Re: UDP is open but TCP isn't
« Reply #1 on: June 02, 2016, 01:12:28 PM »