LinuxQuestions.org - Is there a service that binds and listens to unused ports?

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Is there a service that binds and listens to unused ports?

Hello, I have a server that is behind a network firewall. I wish to know what ports the firewall lets through to this server. The only way I can think of testing this would be to run a bunch of services and make them listen on a bunch of ports on the server and then run nmap and scan the server. Does anyone know of some all-in-one service that will bind to unused ports in a specific range and listen on them so that I can scan with nmap?

Thanks!

Hi,

You could conceivably use the "swiss army knife" of networking
for this ... have a look at netcat (nc for short).

Cheers,
Tink

Yeah Tinkster pointed it right, see this example.

Code:

bash $ nc -zuvv 192.168.1.27 30118-30121

airtelussd1 [10.2.45.197] 30121 (?) open

airtelussd1 [10.2.45.197] 30120 (?) open

airtelussd1 [10.2.45.197] 30119 (?) open

airtelussd1 [10.2.45.197] 30118 (?) : Connection refused

Thanks guys. I am beginning to mess around with netcat, but I'm not getting very far. For instance, I run the following command and nothing seems to happen:

Code:

me@me$ nc -l -p 1234 < /etc/resolv.conf 

usage: nc [-46DdhklnrStUuvzC] [-i interval] [-p source_port]

          [-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_version]

          [-x proxy_address[:port]] [hostname] [port[s]]

From what I've read, I expect it to wait for a connection on 1234 then dump the file to that port. Unfortunately, it seems like I have a usage problem. The -l is supposed to be for "listen" and the -p is supposed to be for "on port."

Same thing happens with the following command:

Code:

me@me$ nc -vv -z -w2 192.168.31.129

usage: nc [-46DdhklnrStUuvzC] [-i interval] [-p source_port]

          [-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_version]

          [-x proxy_address[:port]] [hostname] [port[s]]

Thanks again.

Did you tried my example.

Usage is

Code:

nc -zuvv IP 'range of ports separated by -'

Example

Code:

nc -zuvv 192.168.1.27 30118-30121