I have been trying to create a TCP connection between a client program and a remote server. I am able to form a connection between the two when they are running on the same machine, and any machines connected to my router. However, I am unable to form a connection to any of my friends' computers when I give them the server or client programs, and I am unable to form a connection between my computer and my remote server.
In order to locate the bug, I have shut down the firewalls of both my computer and my server, stopped using my own code and resorted to Netcat. However, the situation remains identical: I can form a server and connect to it with local machines, but cannot form any remote connections.
These are the commands I have been using with Netcat:
nc -vv XXX.XXX.XXX.XXX 1234
nc -l -vv -p 1234
Thanks in advance.
Related
I am running server and client in same system. TCP protocol is used for communication between them. In a scenario where client wants to send packet to server, will it go through network infra (i.e. router, internet etc) and come to server or will it manage transfer within system and ignore network.
If you are on the server, any communication you initiate to IP addresses also on the same server will never leave the server.
You can test by installing tcpdump then running from the console/keyboard/mouse:
tcpdump -n -i enp0s5 not arp
Do not generate network traffic. Try to ssh to your account on IP 127.0.0.1 (e.g. risner#127.0.0.1).
Also try to initiate ssh to another host on the network.
Nothing should show on tcpdump, so that indicates it is not leaving the machine.
I am a complete beginner when it comes to networking and I am trying to set up a TCP tunnel on my machine using pagekite. I want to route all traffic from a TCP address to a port on my localhost, let's say 8080. I would then start a handler on localhost:8080 to deal with the incoming traffic. I can get this to work with ngrok simply by doing ngrok tcp 8080, but on a free ngrok plan I cannot reserve tcp addresses and ngrok is rather slow, so I opted to try and use pagekite.
Pagekite normally allows easy tunnelling to an HTTP address, but they have a guide here about how to use PuTTY along with Pagekite to create a TCP tunnel proxied by HTTP.
I followed their guide but could use some help figuring out if it does what I want it to do.
I am working on a Linux VM, so I first set up an SSH server with openssh like this: sudo service ssh start
I then exposed that SSH server using pagekite like this: python3 pagekite.py 22 ssh:user.pagekite.me
I then started PuTTY, and configured the Host Name to be user.pagekite.me on port 22, setup an HTTP proxy with the proxy hostname user.pagekite.me on port 443 and finally created a tunnel from the PuTTY machine with source port 8080 and destination localhost:8080.
Now I am not sure what this actually accomplished. I know that the PuTTY machine connected to the ssh server running on my VM and I am able to use the linux terminal from the PuTTY terminal but has this actually created a TCP tunnel from user.pagekite.me:8080 to localhost:8080? Additionally after doing this, if I try to setup the handler on localhost:8080 I get the following error:
Handler failed to bind to 0.0.0.0:8080
Rex::BindFailed The address is already in use or unavailable: (0.0.0.0:8080).
Again I am completely clueless when it comes to networking so if anyone could explain what it is I'm doing and if it is even possible to do what I want the way that I am doing it, that would be quite helpful.
I need to open port#42474 on my Windows 10 system for penetration testing purposes.
I added it to the inbound list of my Windows Defender Firewall (both TCP and UDP protocol), and it is enabled.
However, whenever I am trying to ping this port on my machine using telnet it is throwing an error as
Connecting To localhost...Could not open connection to the host, on port 42474: Connect failed
I am able to use telnet to ping other sites such as google.com. But not this port on my machine. Below is the command I am running to test the port and the error:
Port
Telnet error
telnet localhost 42474
Do I need to do anything else to open port#42474?
How do I verify if this port is available for use?
TCP ports are bi-directional, so check these tips:
Verify your service on this port is running: netstat -a
Be sure your firewall isn't blocking (try to deactivate it: if it works well, your rule isn't correct)
Search for your service log: maybe,
it receive information, but it's not able to reply. I recommend you to use PuTTY or Kitty (which is my favorite, because it's portable without registry keys modification), and try to connect on this port.
If you need a tool that able to listen on the port, see this post: Utility to open TCP port to listen state and netcat.
You can use the Python programming language. More specifically, the socket library:
import socket
hote = "localhost"
port = 4444
socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
socket.connect((hote, port))
print "Connection on {}".format(port)
socket.send(u"Hey my name is Abdx!")
print "Close"
socket.close()
I have implement a Client-Server application in java. The server can serve multiple clients, and I want to test that, but my knowledges on Networking is poor, and I need a way to test my application on my home.
I have a rooter, which are connected both of my computers. My "server" class in java uses as host the local host (127.0.0.1) on a given port.
How can I test my program if
The Server.java is running on the Computer A
Server.java is running on 127.0.0.1 on 3943 port
1st Client.java is running on the Computer A
1st Client.java is connected to 3943 port
2nd Client.java is running on the Computer B
2nd Client.java is connected to 3943 port
Any ideas?
Use unique ports for the clients and servers running on the same machine. In addition 127.0.0.1 is localhost (internal to that machine). Computer B cannot communicate with 127.0.0.1 on Computer A. Use 127.0.0.1 if all applications or on the same machine. Use the computers actual IP address if you want external machines to be able to communicate with the server.
When client and server, are on the same computer, what you are doing must be already working.
To connect from a different computer, you need to find the "real" ip address of your server.
If you are on Windows, open a command shell on your computer A, and run ipconfig. On unix/linux/mac, run ifconfig.
Look for a string, looking like an ip address, but not 127.0.0.1, there has to be another one if you are connected to a network, probably looks like 10.0.0. or 192.168.<0 or 1> ..
Use this address everywhere instead of 127.0.0.1
A full TCP connection consists of two different endpoints. The server side of the connection is one endpoint (it will be do a listen on that endpoint). When a client creates it's side of the connection (the client socket), it will do a connect to the server ip:port combo and get a number assigned from a range of so-called "ephemeral" ports.
The fact that both sides of the connection have the same IP address doesn't matter - the full connection is defined by two distinct elements (address:port combinations).
FirstClient's connection to the server will be ServerIP:ServerPort<->Client1_IP:Client1_Port, and SecondClient's connection will be ServerIP:ServerPort<->Client2_IP:Client2_Port. The network layer can differentiate between these (they are two different connection streams) and route traffic to the appropriate sender/receiver for that stream.
If you run the server bound to IP 127.0.0.1 you are not opening it to the network, only your own computer will be able to connect to it, acessing 127.0.0.1 (loopback IP address).
To open this server to the network, you must do one of the two things:
Bind it to the IP 0.0.0.0 so it will be acessible from all networks;
Bind it to a specific network IP address so that it will be available to that network only.
Its common practice to just bind it to 0.0.0.0, its easier.
Once its done, you will be able to connect from other computers to the server running on computer A, however, not through IP 127.0.0.1. Thats the loopback address and can only be used by a computer to connect to itself.
Computer A can use the IP 127.0.0.1 to connect to the server since the server is running on it, but other network computers will have to specify computer A's network IP address.
You can find your IP address on the network adapter details, or running the command ipconfig /all on a command prompt (Windows) or ifconfig (Linux).
I got access via SSH (root access) to a Machine that's inside a network at my client's office.
I'm programming in my computer a PHP application that needs to integrate to LDAP. The LDAP server is in another server at my client's network and not accesible from outside, however I can perfectly access it via the server I can connect to via SSH.
My question is: IS there anyway I can make a tunnel and setup a port in my computer to get the traffic forwarded to the LDAP server using my SSH connection to one of the computers on the network?
Thanks!!!!
Yes, ssh has a "-L" option to create a tunnel. That option takes 3 parameters, separated by colons (:). Local listen port, remote host, remote port.
ssh -L 9999:ldapserver:389 user#otherhost
Where 9999 is the local port that the tunnel will be created on. The ldapserver:389 bit tells it where to connect to on the other side.
Then, tell your application to connect to localhost:9999 (or whatever port you choose) and it will be tunneled across.