Please explain this netcat output

r.stiltskin · 02-23-2016, 06:11 PM

I'm having trouble trying to connect to an ffmpeg stream -- it's giving some "connection refused" errors:

Code:

[tcp @ 0x28d1f60] Connection to tcp://localhost:8080 failed (Connection refused), trying next address
Tue Feb 23 19:01:29 2016 127.0.0.1 - - New connection: GET /webcam.ffm
Tue Feb 23 19:01:29 2016 127.0.0.1 - - [GET] "/webcam.ffm HTTP/1.1" 200 20559
[tcp @ 0x28d4380] Connection to tcp://localhost:8080 failed (Connection refused), trying next address
Tue Feb 23 19:01:29 2016 127.0.0.1 - - New connection: POST /webcam.ffm

and I'm trying to figure out why.

I ran
~ $ nc -z -v localhost 8080

and the output is

Code:

nc: connect to localhost port 8080 (tcp) failed: Connection refused
Connection to localhost 8080 port [tcp/http-alt] succeeded!
Tue Feb 23 19:08:49 2016 127.0.0.1 - - [] " " 200 0

So why is connection refused for tcp but succeeded for tcp/http-alt? What does this output mean?

jefro · 02-23-2016, 08:26 PM

Maybe this. That the port is open for one use because some other process behind it is available?
"
Working Example

Here’s a few basic examples which show how it’s used to test network connectivity. Note that extent of the tests is just to check whether the port is listening, and not the nature of the daemon or whether it’s working. In every case, I’ll assume once again that our listening host is called “davros”.

Test that the Tomcat port (tcp/8080) is listening and accessible

# nc -v davros 8080
Connection to davros 8080 port [tcp/http-alt] succeeded!
"
http://www.terminalinflection.com/us...-connectivity/

Also

"The -z switch prevents sending any data to a TCP connection and very
limited probe data to a UDP connection, and is thus useful as a fast scanning
mode just to see what ports the target is listening on."

So my guess is -v said check and report, -z said don't send any data.

r.stiltskin · 02-23-2016, 11:38 PM

But why 2 lines of output, the first saying connection refused and the second connection succeeded?

jmoore@thebank.com · 02-24-2016, 09:27 AM

Check /etc/hosts. I'll bet that localhost resolves to both ::1 (IPv6) and 127.0.0.1 (IPv4) and that your web service is only listening on one of the addresses, probably IPv4, or that the local firewall is blocking access to that port on one of the addresses. When you give netcat the 'localhost' address for a TCP connection it tries every IP address that name resolves to until it gets a connection or has tried them all.

r.stiltskin · 02-24-2016, 11:33 AM

That seems to be it. Thanks.

jefro · 02-24-2016, 04:47 PM

Yea!! Thanks for the solution and update.