I have a server set-up with netcat:
nc -l 4444 -u
And a client:
nc 127.0.0.1 4444 -u
I am using localhost because they are both on my computer, but if the client moves to another computer, is there a way for netcat to tell me the ip address and port number of the client?
Use the -v or -vv for verbose logging, that will tell you client IP and port.
Related
I have a google compute running CentOS 7, and I wrote up a quick test to try and communicate with it over port 9000 (from my home PC) - but I'm unexpectedly getting network errors.
This happens both with my test script (which attempts to send a payload) and even with plink.exe (which I'm just using to check the port availability).
>plink.exe -v -raw -P 9000 <external_IP>
Connecting to <external_IP> port 9000
Failed to connect to <external_IP>: Network error: Connection refused
Network error: Connection refused
FATAL ERROR: Network error: Connection refused
I've added my external IP to googles firewall (https://console.cloud.google.com/networking/firewalls) and set to allow ingress traffic over port 9000 (it's the lowest priority, at 1000)
I also updated firewalld in CentOS to allow TCP traffic over the port:
Redirecting to /bin/systemctl start firewalld.service
[foo#bar ~]$ sudo firewall-cmd --zone=public --add-port=9000/tcp --permanent
success
[foo#bar ~]$ sudo firewall-cmd --reload
success
I've confirmed my listener is running on port 9000
[foo#bar ~]$ netstat -npae | grep 9000
(Not all processes could be identified, non-owned process info
will not be shown, you would have to be root to see it all.)
tcp 0 0 127.0.0.1:9000 0.0.0.0:* LISTEN 1000 18381 1201/python3
By default, CentOS 7 doesn't use iptables (just to be sure, I confirmed it wasn't running)
Am I missing something?
NOTE: Actual external IP replaced with <external_IP> placeholder
Update:
If I nmap my listener over port 9000 from the CentOS 7 compute instance over a local IP, like 127.0.0.1 I get some results. Interestingly, if I make the same nmap call over the servers external IP -- nadda. So this has to be a firewall, right?
external call
[foo#bar~]$ nmap <external_IP> -Pn
Starting Nmap 6.40 ( http://nmap.org ) at 2020-05-25 00:33 UTC
Nmap scan report for <external_IP>.bc.googleusercontent.com (<external_IP>)
Host is up (0.00043s latency).
Not shown: 998 filtered ports
PORT STATE SERVICE
22/tcp open ssh
3389/tcp closed ms-wbt-server
Nmap done: 1 IP address (1 host up) scanned in 4.87 seconds
Internal Call
[foo#bar~]$ nmap 127.0.0.1 -Pn
Starting Nmap 6.40 ( http://nmap.org ) at 2020-05-25 04:36 UTC
Nmap scan report for localhost (127.0.0.1)
Host is up (0.010s latency).
Not shown: 997 closed ports
PORT STATE SERVICE
22/tcp open ssh
25/tcp open smtp
9000/tcp open cslistener
Nmap done: 1 IP address (1 host up) scanned in 0.10 seconds
In this case software running on the backend VM must be listening any IP (0.0.0.0 or ::), your's is listening to "127.0.0.1:9000" and it should be "0.0.0.0:9000".
The way to fix that it's to change the service config to listen to 0.0.0.0 instead of 127.0.0.1 .
Cheers.
I have a virtual machine located inside a private network.
So firstly, I should come in server.com and then come in my-machine.
I want to make ssh-tunnel from my laptop to my-machine.
ssh -v -A -nNT -L 40000:127.0.0.1:40000 login#server.com ssh -v -nNT -L 40000:127.0.0.1:40000 my-machine &
Now I want to test ssh-tunnel with netcat.
I run at my-machine:
nc -l 40000
At my laptop:
~ ❯❯❯ nc 127.0.0.1 40000
But it gives me:
debug1: Connection to port 40000 forwarding to 127.0.0.1 port 40000 requested.
debug1: channel 2: new [direct-tcpip]
channel 2: open failed: connect failed: Connection refused
debug1: channel 2: free: direct-tcpip: listening port 40000 for 127.0.0.1 port 40000, connect from 127.0.0.1 port 49692 to 127.0.0.1 port 40000, nchannels 3
Why this happen and how to fix it? I expected that anything I type in my laptop console will appear in my-machine console.
What last string means? Especially 127.0.0.1 port 49692 why this port is used? I never type it.
debug1: channel 2: free: direct-tcpip: listening port 40000 for 127.0.0.1 port 40000, connect from 127.0.0.1 port 49692 to 127.0.0.1 port 40000, nchannels 3
Every TCP connection is point to point needs two pairs of IP addresses and ports. Reading all the message (not just the part you showed):
connect from 127.0.0.1 port 49692
So indeed you are connecting to the port 40000, but you are connecting from port 49692 (randomly assigned for your netcat or some of the forwarded steps).
How to fix this problem?
This double-jump forwarding does not work, because you need the second established before the first one.
Also you are using -N switch for the first command, which is preventing running the second ssh command.
But I would give it a shot with ProxyCommand, which will make you connect to the destination with single command directly from your host:
ssh -v -nNT -L 40000:127.0.0.1:40000 \
-oProxyCommand="ssh -W %h:%p login#server.com" my-machine &
I have a jetty server running under port 8080 on VM. VM in its turn runs on remote server under port 10000. Is it legit to address it as http://someremote.org:10000:8080/request? Or should I use SSH somehow?
What I was looking for is called ssh tunneling. You make a tunnel from your port to remote's machine port like that:
ssh -p 10000 -L 18080:localhost:8080 user#remote.host.org
18080 here is port, that you use on your local machine in order to get to remote's 8080 port.
i am trying to learn socket programming with PHP but quickly ran into binding errors on ports,now my attention is diverted onto solving port issues, how do i go about fully controlling ports on my machine, what commands do i use?
sudo netcat -z -vv localhost http
localhost [127.0.0.1] 80 (http): Connection refused
my problem is i get connection refused on port 80
and when i run a port scan on my iMac i only get
netcat -v -z -n -w 1 127.0.0.1 1-1023
127.0.0.1 88 (kerberos) open
127.0.0.1 548 (afpovertcp) open
127.0.0.1 631 (ipp) open
how do i add port 80 (http) open
to that list?
any help would be appreciated thanks
I'm trying to send a broadcast message using netcat.
I have firewalls open and sending a regular message like this works for me:
host: nc -l 192.168.1.121 12101
client: echo "hello" | nc 192.168.1.121 12100
But I can't get something like this to work.
host: nc -lu 0.0.0.0 12101
client: echo "hello" | nc -u 255.255.255.255 12100
Am I using the right flags? Note, the host is on Mac and the client on Linux. Can you give me an example that works for broadcasting a message?
Thanks!
The GNU version of netcat might be broken. (I can't get to work under 0.7.1 anyway.) See http://sourceforge.net/p/netcat/bugs/8/
I've gotten socat to work. Code below does UDP broadcast to port 24000.
socat - UDP-DATAGRAM:255.255.255.255:24000,broadcast
(In socat-world "-" means "stdin".)
You're not saying you want to broadcast, which is done using the -b option to nc/netcat.
nc -h 2>&1 | grep -- -b
-b allow broadcasts
A simple example that works on Ubuntu. All the info in is in the other answers, but I had to piece it together, so thought I would share the result.
server
nc -luk 12101
client
echo -n "test data" | nc -u -b 255.255.255.255 12101
The client will hang until you do Ctrl-C
Sorry, if I am assuming wrong but you mentioned that you have your firewalls set up correctly so I am guessing that the host and client are not on the same subnet???
If that is the case and this firewall is also acting also as a router (or if the packet has to go through a router) then it is going to process that packet but it will not forward it out its other interfaces. If you wanted that to happen then you would need to send a directed broadcast. For example; for the subnet 192.168.1.0/24 the directed broadcast would be 192.168.1.255, the last IP in the subnet. Then the firewall, assuming it had a route to 192.168.1.0/24 and that it is set up to forward directed broadcast, would forward that broadcast out to the destination or next hop. Configuring your device to forward directed broadcast... you would need to reference its documentation. For Cisco IOS you would type in, under the interface, "ip directed-broadcast".
255.255.255.255 is a limited broadcast and is not going to get pass your routers regardless, it is solely intended for the layer 2 link that it resides.
As for how netcat is set up:
-l 0.0.0.0 12101, tells netcat to listen on port 12101 on all interfaces that are up and with an IP address assigned. The -u is not needed as it is telling netcat to listen on a unix domain socket, google IPC :) (this is the biggest reason that your scenario is not working.)
The below should work to get a broadcast forwarded to another network via netcat:
server: nc -l 0.0.0.0 12101
host: echo "hello" | nc 192.168.1.255 12101
Hope that helps, sorry if that was long winded or off from what you were looking for :)