I have an AWS Linux 2 instance, with two interfaces in different subnets, where I installed Openvpn using the 172.23.0.0/24 network. Openvpn is working and I can connect to it. However, from the remote client I can only ping the interface connected to the Internet and the Openvpn tunnel interface which has the 172.23.0.1 address. I can not ping the other interface with the 10.0.0.8 address. From the instance, I can ping all addresses. If I run tcpdump, I can see the packets arriving from the remote client, but the interface does not respond.
I have stoped source and destination check and I have also activated ip forwarding with sysctl -w net.ipv4.ip_forward=1 and even tried sysctl -w net.ipv4.conf.all.proxy_arp=1 and sysctl -w net.ipv4.conf.all.proxy_arp_pvlan=1. This is a brand new instance where the only thing installed is Openvpn. No firewall.
Can not figure this out and would appreciate some help.
I´ve got a Server behind a firewall and the firewall only allows traffic through port 22. This server has both public and private addresses.
I´ve got also about 1K clients that I need to reverse shell to this server, and be able to choose one of them by id when I want that ssh reversed tunnel.
My goal is to make the clients connect to ssh server via port 22, and each one of this connections should be forwarded to localhost on port with the same id.
When I connect to the server with my laptop also via ssh, I would then ssh to localhost on the correct id and get the client shell.
Can someone provide me the good path to achieve this behaviour using bash, ssh and linux tools?
Note - I don´t want to use client.py and server.py cause most of my clients are android based and it could easily become a nightmare to install python on all of them.
The problem - it was solved using remote port forwarding:
ssh -R 21:localhost:8888 user#server
In this command the 8888 represents the terminal id. In order for this to work, had to add this line to my ssh conf:
GatewayPorts yes
My lab runs RStudio on a server. A couple weeks ago, from my cousin's house, I successfully ssh'd into the server and pulled up the server-side RStudio through my local Firefox browser. Now when I try to access the server RStudio from home (via my own router), it doesn't work. I need help troubleshooting, and I'm guessing it's some problem on the router. I'm running Mac OSX 10.6.8. No idea what the university server's running, but I don't think it's a server-side problem.
Here's how it worked the first time I did it, at my cousin's house: first, I VPN into the university network; then I call SSH with port forwarding; then I open a Firefox browser, connect to my localhost port, and it opens up RStudio on the server side which I can access through my local browser window.
Here's the problem I'm having right now when I try to log-in from my home network:
I can make the VPN connection successfully. I can also set up SSH successfully with this command:
ssh -v -L 8783:localhost:8783 myacct#server.com
Here are the last several lines of the verbose output from the successful ssh command:
debug1: Authentication succeeded (password).
debug1: Local connections to LOCALHOST:8783 forwarded to remote address localhost:8783
debug1: Local forwarding listening on 127.0.0.1 port 8783.
debug1: channel 0: new [port listener]
debug1: Local forwarding listening on ::1 port 8783.
debug1: channel 1: new [port listener]
debug1: channel 2: new [client-session]
debug1: Entering interactive session.
Last login: Mon Sep 2 04:02:40 2013 from vpnipaddress
So I think I'm still succeeding at the VPN and SSH stage (though I don't know why it says my last login was Sep 2 when I've logged in a few times since then).
Next, I open Firefox, and I type localhost:8783, and instead of getting an RStudio server app through my browser window, I get the following errors:
In the Firefox browser window, it says: Server not found, Firefox can't find the server at www.localhost.com, Check the address for typing errors etc.
In the terminal window, it says:
debug1: Connection to port 8783 forwarding to localhost port 8783 requested.
debug1: channel 3: new [direct-tcpip]
channel 3: open failed: connect failed: Connection refused
debug1: channel 3: free: direct-tcpip: listening port 8783 for localhost port 8783, connect from 127.0.0.1 port 50420, nchannels 4
I'm not sure what I've got wrong. I haven't changed anything on my laptop since my last successful connection. I'm on my own router (instead of my cousin's), so maybe I need to mess with the firewall? I already allowed ports 22 and 8783 to come through the firewall to my laptop (I'm not even sure I needed to do that though). Help?
ssh -v -L 8783:localhost:8783 myacct#server.com
...
channel 3: open failed: connect failed: Connection refused
When you connect to port 8783 on your local system, that connection is tunneled through your ssh link to the ssh server on server.com. From there, the ssh server makes TCP connection to localhost port 8783 and relays data between the tunneled connection and the connection to target of the tunnel.
The "connection refused" error is coming from the ssh server on server.com when it tries to make the TCP connection to the target of the tunnel. "Connection refused" means that a connection attempt was rejected. The simplest explanation for the rejection is that, on server.com, there's nothing listening for connections on localhost port 8783. In other words, the server software that you were trying to tunnel to isn't running, or else it is running but it's not listening on that port.
Posting this to help someone.
Symptom:
channel 2: open failed: connect failed: Connection refused
debug1: channel 2: free: direct-tcpip:
listening port 8890 for 169.254.76.1 port 8890,
connect from ::1 port 52337 to ::1 port 8890, nchannels 8
My scenario; i had to use the remote server as a bastion host to connect elsewhere. Final Destination/Target: 169.254.76.1, port 8890. Through intermediary server with public ip: ec2-54-162-180-7.compute-1.amazonaws.com
SSH local port forwarding command:
ssh -i ~/keys/dev.tst -vnNT -L :8890:169.254.76.1:8890
glue#ec2-54-162-180-7.compute-1.amazonaws.com
What the problem was:
There was no service bound on port 8890 in the target host. i had forgotten to start the service.
How did i trouble shoot:
SSH into bastion host and then do curl.
Hope this helps.
Note: localhost is the hostname for an address using the local (loopback) network interface, and 127.0.0.1 is its IP in the IPv4 network standard (it's ::1 in IPv6). 0.0.0.0 is the IPv4 standard "current network" IP address.
I experienced this error with a Docker setup. I had a Docker container running on an external server, and I'd (correctly) mapped its ports out as 127.0.0.1:9232:9232. By port-forwarding ssh remote -L 9232:127.0.0.1:9232, I'd expected to be able to communicate with the remote server's port 9232 as if it were my own local port.
It turned out that the Docker container was internally running its process on 127.0.0.1:9232 rather than 0.0.0.0:9232, and so even though I'd specified the container's port-mappings correctly, they weren't on the correct interface for being mapped out.
In my case, it worked after running the vncserver on linux.
Entered this on linux command line : sudo ssh -L 5901:localhost:5901 -i <ssh_private_key> <username>#<public-IP-address>
Type there vncserver
Go to VncViewer application and connect using localhost:5901
I used to meet the similar problem because 'localhost' was not available on server when it restarted network service, e.g. 'ifdown -a' but followed by only 'ifup -eo1'. Besides server is not listening to the port, you can also check 'localhost' is available or not.
ps: Post it just hope someone who has the similar problem may benefit.
I had this problem when I wanted to make a vnc connection via a tunnel.
But the vncserver was not running.
I solved it by opening the channel on the remote machine with vncserver :3.
In my case, it worked after checking the correct IP address of the user credentials
previously I was using the wrong IP of the server
ssh -NfL 127.0.0.1:8084:127.0.0.1:8888 user#ip_address_of_server
after correcting it, works fine.
Encountered with the same error.
In my case, I found the problem was in the config file of jupyter.
Let's say there are 3 computers named A, B, and C, and A can access B but can't access C; B can access C.
To access jupyter-notebook service of C from A, first I established ssh tunnel from A to C through B, then I access jupyter-notebook by typing localhost:port_number, then I got the error.
Finally the problem was solved by writing the "c.NotebookApp.ip = '0.0.0.0'" in jupyter-notebook's config file, where '0.0.0.0' allows the access of other IPs.
Hope someone in a similar situation may benefit.
I had the same error when I was trying to tunnel my mlflow ui over ssh to view remotely. As mentioned in the first answer, the error arises because nothing on the server is listening for the port. This, for me, is because I forgot to start the mlflow app on my remote machine! So in general – make sure the app you're trying to access remotely is running.
Just replace localhost with 127.0.0.1.
(The answer is based on answers of other people on this page.)
This means the remote vm is not listening to current port i solved this by adding the port in the vm server
I am using netcat to send file over my campus network.
I have used
c:\nc -w200 10.x.x.x 9638 < file.txt
on my client machine and
c:\nc -v -L -p 9638 >> nc.out
on my computer that is working as a server to receive files.
It worked completely fine when i tested it using localhost hence sending and receiving files on my system only.I am using the netcat version without the GAPING_SECURITY_HOLE downloaded from http://www.rodneybeede.com/Compile_Netcat_on_Windows_using_MinGW.html.
Our systems are connected to the net using proxy servers. Could they be interfering? Also pinging computers is disabled.
I am working on windows for now.
Yes proxy and router may interfere.
Try to see if you can telnet to that port
telnet <ip> port
That will tell you if you can access that machine on that port
A service, for example an FTP server, only accepts connections from a specific network, where all users will have the same external IP-adress.
I want to connect to this service, but I'm currently not inside the allowed network.
I have ssh access to a server inside the network.
How do I use ssh to tunnel a certain port from my local machine, through a machine on the internal network, to the final service, so that any client opening the correct port won't notice any difference?
You can create a SSH tunnel to your specific network using the following command.
For instance, let's say you want to reach a web service on computer "mywebserver" (port 80).
Under Linux or BSD, using OpenSSH, you can use the following commandline:
ssh -f mysshserver -L 1234:mywebserver:80 -N
Under Windows, you can use MobaXterm which includes a simple graphical ssh tunnel builder
This will open a SSH tunnel between local port 1234 and remote webserver on port 80. You can then open your web browser and connect directly to your web server by typing "http://localhost:1234" in the address bar.