How to proxy and tunnel one IP Address via SSH?

Question

I have two servers: A and B.

Server A is my main server which hosts my website (in my country). Server B is a server in the US.

I have limit to connect to some websites via server A, so I want to create a tunnel or proxy (not sure which one is suitable) from A to B, so that, sending request from A to blocked-site.com is proxied to B. So:

server A proxies request to B
server B sends request to blocked-site.com
the website answers to B
B answers to A

I tried this command:

ssh -vL 1080:blocked-site.com:1080 root@server-b

Bit when I run nslookup blocked-site.com I do not get any answers.

Answer 1

The command ssh -vL 1080:blocked-site.com:1080 root@server-b will create a local port 1080 that will be tunneled to blocked-site.com:1080. With this tunnel you can access blocked-site.com:1080 using localhost:1080. So to be able to access blocked-site.com:1080 you have to replace blocked-site.com:1080 by localhost:1080 (e.g. telnet localhost:1080).

nslookup does not know that localhost:1080 is tunneled to blocked-site.com:1080 so it still tries to directly access blocked-site.com:1080

Take into account that the set up tunnel only works if server B allows it. Because this is a security risk this is not always (usually) not the case.

One way to be able to access blocked-site.com:1080 without changing the client call is (assuming server A is a Linux machine):

Add the following line to /etc/hosts:

127.0.0.2 blocked-site.com

Even with the above line added to /etc/hosts nslookup will still not work, but you will see that ping blocked-site.com will now ping 127.0.0.2.

The reason that the nslookup will not be effected by the set up SSH tunnel is that nslookup sends a request to the DNS server using UDP port 53 while localhost TCP port 1080 is tunneled.