This feels like a basic question, I'm sure other people needed something like this at some point however I couldn't find anything clear on this topic and I'm not very familiar to networking so I hope following makes sense (and sorry if I am butchering the terminology)
I often need to connect to a VPN server at work. At the moment I am using Cisco AnyConnect, which upon connection asks me the host server, my username, my password and routes all my traffic through the VPN afterwards.
The problem is, depending on what I'm doing I often need to jump back and forth to VPN (some applications need local network and others dont)
What would be perfect is to create one VPN connection and just keep it on a port without routing anything to it. Then I can use it as a proxy to selectively route my traffic through VPN (eg. I override http_proxy locally on one terminal instance and run applications that require VPN through there without having to jump back and forth). Furthermore if I create this connection from the terminal I can automate most of the process, with something like:
function callExecutableThroughVPN() {
if ! is_connected_to_vpn then
echo "coulnt find the vpn connection, will attempt to connect. enter password:"
# get password input here
setup_vpn_on_port_9876 # pass password input here
echo "setting proxy to 127.0.0.1:9876"
http_proxy=127.0.0.1:9876/
https_proxy=127.0.0.1:9876/
fi
./executable_that_need_vpn
}
Then I can simply stay on my network and use a wrapper like above for few processes that require their traffic re-routed.
So in summary, my question is: Is it possible to create a single VPN process through terminal to listen a local port, so I dont have to route all my traffic at once, and I can simply kill this process when I'm done
I recommend using SSH tunnel/Socks Proxy (see ssh -D) and tsocks wrapper. For http(s) proxies I recommend the proxychains tool.
Related
I am setting up port scanner for remote server in my application using Go. I am using DialTimeout function in Go net package to check whether a remote host port is opened or not. The result is fine with success case. But, if i/o timeout happens, I need to identify whether
The port is closed (No service is running) or
Port is blocked (Firewall filtered) or
Due to internet connectivity down in local system where the application is running.
Have tried nmap cli command, I can able to differentiate those failure 3 cases exactly.
nmap command tried: nmap -sA -p port_number host_ip
I found a Go 3rd party libray to use nmap.
But, I don't want to use nmap in my application. Are there any other alternatives in Go to exactly differentiate those 3 cases?
In the simple world
Lets assume you want to scan a Linux system.
If you get an ICMP message type 3 code 3, the firewall explicitly told you:
Hi, I am the firewall of your target host. The host is running. I hereby inform you that you (potentially amongst others) can not access this port. So now that you know you should quit your connection attempts. However, I won't tell you wether it is because there is no service running behind it (in which case my response is simply a courtesy) or because I was told to deny you access. Goodbye!
The port is closed if you do not get above answer and can not make a connection. I hence strongly advice to use context.WithTimeout to make a connection.
In the real world
However, this only applies if the admin of the target host did not change the ICMP message type to respond with - or chose just to drop any packets coming from sources which are not allowed to access the respective service. In the latter case, there is no way for you to know wether the port is closed or filtered.
All of the above only applies if we are talking of an iptables based firewall on the target system with default settings.
Now assume something which is by far more likely: A border firewall plus a local firewall. The border firewall might send other ICMP messages (or, again, simply drop your packages). Those rules apply additionally to the rules of the local firewall. So it is a misconception that you are actually scanning a host. It is more accurate to say that you scan the services reachable via a specific IP.
EDIT
Why would one send an ICMP message explicitly rejecting connection attempts?
There are various reasons to come to that decision. There is a good answer on serverfault.com
In my current setup I have two interfaces, one is my normal connection and the other for my VPN, which is the default interface.
My VPN isn't nearly as fast as my connection so for some heavier load I use my normal connection. The problem I am having is that I want to send files to Google Drive by using their api via CMD, but googleapis.com simply resolves to too many IP's to route them all. Currently I am solving this issue by connecting through a proxy so I only have to route that proxy to my normal interface.
What I would rather do is just set the interface of my normal connection to the CMD session like I do with the proxy. I have tried playing around with netsh but so far with no success.
Does anyone have an idea on how to solve this problem?
It isn;t that your VPN is your "Default Interface" it's that it has a Lower Route Metric for Traffic because whoever set it up made it so that all traffic routes t the VPN instead of only internal traffic.
If this is intentional, and you don;t want to change it then your only real option is to use a Proxy as you need to be able to sniff the packet headers to match the API URL, and it's it's HTTPS traffic, that is encrypted, and only passing through a proxy will be able to get around that.
This is part programming, part sysadmin, so please excuse me if you feel that this should be over on serverfault.
I have an application that is not SOCKS aware and that we need to use through a firewall. We cannot modify the application to have SOCKS support either.
At the moment, we do this by aliasing the IPs the application talks to the loopback adapter on the host, then creating SSH tunnels out to another host. The IP's the application uses are hardcoded. Our SSH connections look like:
ssh -L 1.2.3.4:9999:1.2.3.4:9999 user#somehost
Where 1.2.3.x are aliases on the loopback.
So the application connects to the open port on the loopback, which gets sent out to the SSH host and onto the real 1.2.3.4.
It works, but the problem is that this application connects to quite a few IPs ( 50+ ), so we end up with 50 ssh connections out from the box.
We've tried to use several 'proxifying' apps, like tsocks and others but have had alot of issues with them ( the app is running on OS X and tsocks doesn't work so well, even with the patches )
Our idea was to write a daemon that listened on all interfaces on the specified port - it would then take the incoming packets from the application, scrape the packet info ( dst IP, port, payload ), recreate the packet and proxify it through a single SSH SOCKS connection ( ssh -D 1080 user#somehost ). That way, we only have 1 SSH connection that all the ports are being proxied through.
My question is - is this feasible? Is there something that I'm missing here? I've been combing through pfctl, ipfw, iptables docs, but I don't see any option to do it through those and this doesn't seem like it'd be the most difficult thing to code. It would recreate the packet based on the original destination IP and port, connect to the local SOCKs proxy and resend the packet as if it were the original application, but now with SOCKS support.
If I'm missing something that someone knows about that already does this, please let me know. I don't know socket programming or SOCKs too well, but this doesn't seem like it'd be too big of a project to tackle, but I'd like some opinions if I'm biting off way more that I should.
Thanks
If your application could add SOCKS client support, you can simply ssh -D lock_socks_port remote_machine, which will open up the local *lock_socks_port* as a SOCKS server at localhost, which can then connect to any host accesible by the remote machine.
Example: imagine you are using an untrusted wifi network without encryption. You can simply launch ssh -D 1082 home, and then configure your web browser to use localhost:1080 as SOCKS server. Of course, you need a SOCKS-enabled client. All the traffic would appear as coming from your gateway, and the connection would be opaque to those snooping the wifi.
You can also open a single ssh client with an indefinite number of LocalForward requests, which would be tunneled on top of a single ssh session.
Moreover, you can add ssh connections to an already-established ssh connection by using the ControlMaster and ControlPath options of ssh.
Most proxy servers perform the job of forwarding data to an appropriate "real" server. However, I am in the process of designing a distributed system in which when the "proxy" receives a TCP/IP socket connection, the remote system actually connects with a real server which the proxy nominates. All subsequent data flows from remote to the real server.
So is it possible to "forward" the socket connection request so that the remote system connects with the real server?
(I am assuming for the moment that nothing further can be done with the remote system. Ie the proxy can't respond to the connection by sending the IP address of the actual server and the remote connections with that. )
This will be under vanilla Windows (not Server), so can't use cunning stuff like TCPCP.
I assume your "remote system" is the one that initiates connection attempts, i.e. client of the proxy.
If I get this right: when the "remote system" wants to connect somewhere, you want the "proxy server" to decide where the connection will really go ("real server"). When the decision is made, you don't want to involve the proxy server any further - the data of the connection should not pass the proxy, but go directly between the "remote system" and the "real server".
Problem is, if you want the connection to be truly direct, the "remote system" must know the IP address of of the "real server", and vice versa.
(I am assuming for the moment that nothing further can be done with
the remote system. Ie the proxy can't respond to the connection by
sending the IP address of the actual server and the remote connections
with that. )
Like I said, not possible. Why is it a problem to have the "proxy" send back the actual IP address?
Is it security - you want to make sure the connection really goes where the proxy wanted? If that's the case, you don't have an option - you have to compromise. Either the proxy forwards all the data, and it knows where the data is going, or let the client connect itself, but you don't have control where it connects.
Most networking problems can be solved as long as you have complete control over the entire network. Here, for instance, you could involve routers on the path between the "remote system" and the "real client", to make sure the connection is direct and that it goes where the proxy wanted. But this is complex, and probably not an option in practice (since you may not have control over those routers).
A compromise may be to have several "relay servers" distributed around the network that will forward the connections instead of having the actual proxy server forward them. When a proxy makes a decision, it finds the best (closest) relay server, tells it about the connection, then orders the client to connect to the relay server, which makes sure the connection goes where the proxy intended it to go.
There might be a way of doing this but you need to use a Windows driver to achieve it. I've not tried this when the connection comes from an IP other than localhost, but it might work.
Take a look at NetFilter SDK. There's a trial version which is fully functional up to 100000 TCP and UDP connections. The other possibility is to write a Windows driver yourself, but this is non-trivial.
http://www.netfiltersdk.com
Basically it works as follows:
1) You create a class which inherits from NF_EventHandler. In there you can provide your own implementation of methods like tcpConnectRequest to allow you to redirect TCP connections somewhere else.
2) You initialize the library with a call to nf_init. This provides the link between the driver and your proxy, as you provide an instance of your NF_EventHandler implementation to it.
There are also some example programs for you to see the redirection happening. For example, to redirect a connection on port 80 from process id 214 to 127.0.0.0:8081, you can run:
TcpRedirector.exe -p 80 -pid 214 -r 127.0.0.1:8081
For your proxy, this would be used as follows:
1) Connect from your client application to the proxy.
2) The connection request is intercepted by NetFilterSDK (tcpConnectRequest) and the connection endpoint is modified to connect to the server the proxy chooses. This is the crucial bit because your connection is coming from outside and this is the part that may not work.
Sounds like routing problem, one layer lower than TCP/IP;
You're actually looking for ARP like proxy:
I'd say you need to manage ARP packets, chekcing the ARP requests:
CLIENT -> WHOIS PROXY.MAC
PROXY -> PROXY.IP is SERVER.IP
Then normal socket connection via TCP/IP from client to server.
If I create a c++ server/client application, the port I used to communicate does it need to be open on the router of the server and client machine
Or what other approach could I take? the client computer needs to receive information from the server but I am not able to have any ports opened because it is on a school network....
[edit]
Hmm My setup is a php page running on a server say when I press hello, the server makes a ssh connection through php and sends shell commands to the machine. The server is running off of a school server which I do have ssh access to and run all my things from there. The client computer will be my pc running off of the school wifi which is not connected to the server. The server will try to make a ssh connection to the public ip of my computer running off of the school wifi(no ports open/can ssh out but no ssh in). Will these methods you mention make this possible, in particular the connect.c since I can't run putty off of the server, and the connect.c I could call from the php.
The choice of language is highly irrelevant here.
There don't need to be ports 'open' on any router, unless your traffic must pass through it. On normal peer hosts in the same network (or subnet) there would hardly be any firewall policy, not even in schools.
Technically it is possible for the switch to block peer-2-peer traffic (meaning traffic not destined to the outgoing gateway), but that is not very usual.
Of course, if the school doesn't allow outbound (WAN) traffic on most ports, tough luck, and they're absolutely right :)
You can look at
ssh (with tunnels -L, -D and -R options, perhaps -o GatewayPorts on)
stunnel
connect.c
http-tunnel
All very readily googled
To establish a TCP/IP connection, only the server port needs to be accessible by the client. The connection is full-duplex, therefore data can flow from the client to the server and vice-versa.
If you are using UDP for your application, which is a connection-less protocol, what happens depends heavily on the firewall or router and whether it performs connection tracking for your service or not.
Unless you provide some additional information on your service and the network setup on both the client and the server side, we cannot provide more concrete information.