SSH Tunnels How-to?

The_Spider asks: "I periodically browse the net and check web-mail at work, when I have the opportunity. I was wondering if anyone had a nice walkthrough on how to set-up an SSH tunnel. I'm not 100% newbish to Linux but I don't know where to start. (I have a Fedora Core box at home for NAT & DHCP) I'm hoping to combine this for use with portable Firefox. I'm not to worried about security, but I love the notion of taking a portable and encrypted browser with me from place to place. Can Slashdot help?" While this might be a bit FAQ, I figure Slashdot anecdotes on the use of SSH tunnels might be a bit more user-friendly than say, the several task-specific HOWTOs one can find via a Google search. ALso, I'm sure that there are a few of you out there who have discovered interesting ways of using SSH tunnels, not covered by said HOWTOs. So, how are you using SSH tunnels, and can you explain them to those who have not yet discovered the value of their use?

Comments

Java VNC over SSH

[slthytove]

This doesn't really address the author's original inquiry, but it is (what I would consider) an interesting use of SSH tunnels, in a readable tutorial. I set up something similar to "GoToMyPC" for my Dad, that allows web-based (over JavaVNC) secure remote access to his computers:

Java VNC over SSH

Just what you are looking for...

[linuxkrn]

Got one of those on my website.

Enjoy http://www.linuxlogin.com/linux/admin/sshtunnels.p hp

Reading between the lines...

[Anonymous Coward]

Spider is an employer that wants to block SSH tunnel access for his employees, but he has no idea how to pull it off, so he concocted this excuse about wanting to use our beloved Firefox.

I think we can all collectively say: Spider, go RFTM. :-)
(Yes, the man page for ssh covers this in detail.)

-= End of thread =-

Try the HowTo...

[Anonymous Cumshot]

here: http://www.revsys.com/writings/quicktips/ssh-tunne l.html

It's nice and short, but covers the basics.

Gotta love SSH tunneling

[The Blue Meanie]

I *really* hope my employer doesn't recognize my Slashdot ID. :)

I use an SSH tunnel to forward port 8080 on my desktop machine here at work to port 8080 on my Unix workstation at home that's running an HTTP proxy. I set my Firefox/Mozilla at work to use localhost as its proxy, and I now happily bypass any and all logging and/or site restrictions on my work browsing habits.

I also remote-forward a pseudo-random high port on that remote workstation at home to port 22 on my work desktop machine, giving me the ability to SSH *back in* to work from home, and not monkey with the company's VPN solution that has a client for my home machine that's so buggy it's unreal. That remote SSH call-back also forwards the home machine's IMAP port to the company's Exchange Server so I can read my email over the tunnel, and I port-forward to our network monitoring and backup systems' web interfaces so I can actually do my job.

I guess I can say that my productivity from home would be pretty much zippo if I didn't have SSH tunnels at my disposal.

Re:Gotta love SSH tunneling

[fimbulvetr]

This is exactly what I do, and let me tell you what: It's saved my ass a few times.

I also run two browser profiles with one being the proxied and one being normal, with different shortcuts to each. I separate the instances so my employer still sees a lot of traffic so they don't get suspicious. The work-related ones get me to lots of vendors sites, googling for solutions, etc.

I use a sh script to start my second one. It looks for an already open port just in case I killed the browser accidently and don't need to re-establish the tunnel. It re-establishes if it needs to.

You could also proxy your IM messages through these, though I haven't gone to that length yet. Here's my sh script:

#!/bin/sh

STAT=`netstat -an | grep 8888`;
if [ "$STAT" = "" ];
                then

#friendshomemachine
# ssh -L 8888:127.0.0.1:8888 friendshomemachine "perl -e 'while (1) { print localtime."\n";sleep 10;}'" &
#mine
                ssh -L 8888:127.0.0.1:8888 myhomemachine "perl -e 'while (1) { print localtime."\n";sleep 10;}'" &
#friendshomemachine
# ssh -c blowfish-cbc -C -f -N -L 8888:127.0.0.1:8888 friendshomemachine "perl -e 'while (1) { print localtime."\n";sleep 10;}'" &
#mward
# ssh -c blowfish-cbc -C -f -N -L 8888:127.0.0.1:8888 friendshomemachine "perl -e 'while (1) { print localtime."\n";sleep 10;}'" &

fi /usr/local/firefox/firefox -P encrypted

I've heard blowfish is slower, but it doesn't seem to be when you're just browsing. Feel free to experiment. Others with more knowledge as to what's faster, please let me know.

Re:Gotta love SSH tunneling

[Anonymous Coward]

If I ever caught you pulling that kind of shit in the company where I work, your ass would be out the door so quick your feet wouldn't touch the ground.

There are reasons that the company deploys control mechanisms such as HTTP/SMTP proxies and approved VPN solutions - to protect the corporate infrastructure and information. Yes, you may have SSH access, but that doesn't mean that you should be using that to circumvent the security controls put in place by your employer. Your employer may well be partly to blame for not having made you read their Information Security Policy documents (and get you to sign up in agreement to an AUP). If their policy does not include coverage for things such as the situation you describe above, your security manager & auditors should be beaten heavily and then replaced.

It's this unauthorised, non-standard, "yeah but I can do it better my way for I am a genius" bullshit which ends up causing so many problems in organisations. Yet another glowing example of why the greatest threat to corporate confidentiality, integrity and availability is usually that lurking within.

If you feel that you would be more productive with a different system configuration, did it not occur to you to formally document your suggestion and present it for review under your organisation's change control procedures? It could mean the difference between having a collecting your payslip or clearing your desk.

Re:Gotta love SSH tunneling

[Dausha]

"I *really* hope my employer doesn't recognize my Slashdot ID."

Yes, your employer does know your uid. He's pissed, and he's been logging your activity for some time. He suggests a new shell script:

#!/bin/sh

while (1) {
echo "Get to work, Slacker!";
}

Re:Gotta love SSH tunneling

[ddstreet]

your employer...suggests a new shell script:

#!/bin/sh

while (1) {
echo "Get to work, Slacker!";
}

that's definitely from his manager, since that while statement is completely C and won't run under bash at all!

Re:Gotta love SSH tunneling

[Gothmolly]

I know you shouldn't feed AC trolls, but I'll bite. First, we identify the troll:
1) pedantic reliance on security policy
2) Euro spelling of 'unauthorized'
3) excluded middle fallacy invoked to formally document and submit your request
4) ITIL-like flamage about change control procedures
5) assertion that its wrong de jure, instead of right, de facto

Ok, so now we know it's a troll. What to do?
1) hopefully metamod the positive mods that he received to correct the error
2) offer brief counterargument, demolishing the troll, thus:

You're job is to get work done, and act in the best interests of your employer. If you are doing both, no good manager will complain.

Done.

Here's one...

[Anonymous Coward]

1. Set up usual SSH session settings in Putty
2. Go to Connection -> SSH -> Tunnels
3. Add new forwarded port. Source Port: 1080, Destination: [blank], DYNAMIC (this is important), Auto. Click on Add.
4. In Firefox or any other program that supports a SOCKS proxy, enter host 127.0.0.1 (localhost) with port 1080.

That's it. You'll then be using your SSH connection like a SOCKS proxy.

Re:Here's one...

[spectral]

normal ssh forwards are one-source, one-destination. There are options to allow the entrypoint to the tunnel to come from !localhost, (i.e. I set up an ssh connection from me to my friend, with a tunnel from me to google.com, and now anyone who can connect to me can use that same tunnel to connect to google.com), but normally it really is a one-off thing.

127.0.0.1:1000 goes to www.google.com:80
127.0.0.1:1001 goes to www.porn.com:80
127.0.0.1:1002 goes to www.slashdot.org:80

what using a SOCKS-mimicing "proxy server" allows you to do is to make it so that the requesting application requests the destination, instead of you setting it up and then pointing your computer at a special address. The requesting socks-aware application is like "Hmm, to get to login.messenger.yahoo.com:3697, I must use this special protocol and send stuff really to a connection at 127.0.0.1:4280. I'll do that."

So it connects to that, PuTTY sends it down the wire to my friend, and my friend's computer sends it to login.messenger.yahoo.com, port 3697.

magically. :)

SSH tunnels in Windows (and one-liner for *nix)

[thomasdn]

Some time ago I wrote a little guide on SSH tunnels with PuTTY.
This guide also describes how to setup an SSH tunnel in Linux.

SSL Explorer

[beernutz]

Check out SSL Explorer. It has a windows and linux installer, is easy to use, and is java based, so the client runs pretty much everywhere.

Here's mine

[Dadoo]

We use this actual script (plus a few things I had to edit out for anonymity's sake).

Assuming a Linux machine at each end, here's the script for the machine that initiates the connection:

        while true; do
                pppd nodetach lcp-echo-failure 4 lcp-echo-interval 120 \
                        pty 'ssh receiver -T -l user'
                sleep 10
        done

Where receiver is the public IP address of your receiving machine and user is the username on that machine. The while loop automatically reconnects if you get disconnected.

Here's the script for the machine that receives the connection:

        pids=`ps -e -opid,command | grep "pppd local:remote" | \
                grep -v grep | awk '{print $1}'`

        if [ "$pids" != "" ]; then
                echo "Found pre-existing connection. Killing pids: $pids" >> ppp.log
                kill -15 $pids
                sleep 5
        fi

        pppd local:remote netmask 255.255.255.252 passive \
                notty nodetach

Where local is the local end of your PPP link and remote is the remote end of your PPP link. You'll want to call this script from user's .profile. Remember, this is a private link, so you'll probably want local and remote to be internal addresses, i.e. 192.168.x.x.

My setup

[Evro]

Setup squid on your linux box, listening e.g. on port 3128. Verify that this is working by setting your browser to use it.

To get the tunnel working, I forget the exact settings in putty but there's a section for tunnels, tell it to create tunnel from local port 8128 to remote machine's port 3128. Then set your browser to use "localhost:8128" as your proxy.

The way to setup a tunnel between two Unix boxes (for me) is ssh -L 8128:192.168.0.1:3128 remote-host.

Rewriting & Encrypted Proxy?

[Jherek Carnelian]

I'm just guessing, but wouldn't ssh tunnels be readily identifiable if a smart network admin wanted to look for them?

I'd like to run to a web-proxy at home that I can just point my browser to ala:

https://mycablemodem.cable.net:4567/

that will then access any website and rewrite any internal links to go back through the proxy itself, so for example:

http://www.yahoo.com/ becomes https://mycablemodem.cable.net:4567/http://www.yah oo.com/

Anyone got a good, robust re-writing proxy tool like that? Preferrably with at least some sort of minimal security to prevent joe-random from using it without a login/password.

Re:Rewriting & Encrypted Proxy?

[Daniel Boisvert]

Running it on port 443 is a better idea, because corporate proxies & things like Microsoft's ISA Server expect to see SSL-encrypted traffic on that port. They often disallow encrypted traffic on port 80.

Really Good SSH Tunneling Tutorial

[cyranoVR]

http://souptonuts.sourceforge.net/sshtips.htm

Really good for the beginner - includes information on accessing Samba shares over ssh.

The only way to do work

[Fred Nerk]

I work in a large telco who's security policy is to restrict everything unless explicitly allowed, and the process to get anything allowed is a 3 month long waste of time.

I also have an ssh tunnel established from my work PC to my home connection, and I run pppd over that to create a VPN between my home network and the network at work. I realise that this is probably completely against company policy, but the "official" VPN solution only lets me hit the Exchange server, and doesn't let me actually do any work. Most of the company's "work" involves forwarding emails, so it's probably fine for them.

Unfortunately tcp over tcp is really quite nasty (http://sites.inka.de/sites/bigred/devel/tcp-tcp.h tml) but as nothing else but ssh is allowed out of the firewall at work, I don't have a lot of choice.

A howto that I found quite helpful is at http://www.tldp.org/HOWTO/ppp-ssh/

Anyway.. on to my anecdote (not required reading):

Part of my job involves working on a distributed monitoring system which is deployed in a star topography around the country. All the remote sites send & receive data from one central site (with one redundant central site) using a variety of protocols, like ssh, xmlrpc, dns, telnet, snmp, syslog, etc.

The network was designed by people who were given a set of instructions like "You will use these 2 vendor's systems" and "You must follow these corporate security policies which were written 10 years ago for phone networks", so it's terrible by today's standards (and for an ISP in general).

There are firewalls between all of my boxes, even though all my boxes are on the management lan, and they only allow a very small set of protocols through - not enough to let my software work. That wasn't the worst part. The worst was that the firewalls are also protecting the billing network so have very low tolerances for intrusion detection and flood protection and such. Basically I can only establish 5 connections per second *across the entire network*. This is clearly not enough for a busy monitoring system. So we decided to build a VPN between all of my boxes using ppp on ssh tunnels.

I now have a separate ppp interface from the central server to each of the remote datacenter servers, all on the 10.0.0.0/16 network. ip forwarding is enabled on the central site, so now remote datacenters can talk to each other (also blocked by the firewalls) and I can use all the connections I need to. I'm running quagga ( http://www.quagga.net/ ) on every remote datacenter and the central servers (along with the redundant one) so I can distribute routes to remote datacenter devices and cope with the death of one of the central servers without major service interruption.

However it really is quite slow. I can only get around 200kb/s over each ppp interface even though the physical links are 100+mbit each. But I really don't need huge bandwidth, just some that isn't firewalled.

This "solution" has been in production for 6 months now, and I'm sure as soon as the corporate security people find out they will shut it down and I'll go back to not being able to do my job.

Use PuTTY's 'dynamic' tunneling mode

[zsazsa]

I'm assuming you're on a Windows box. PuTTY's dynamic tunneling mode is the absolute easiest way to tunnel your traffic: it doesn't require setting up a proxy server on the remote system! All you need is an sshd on a server somewhere that allows tunnels. When using dynamic tunneling, PuTTY acts as a local SOCKS proxy. So, just set your browser and other net apps to use a SOCKS proxy on localhost on the port you specify in PuTTY, and you're good to go.

Here's how to do it, using the latest PuTTY and Firefox versions:
1. Configure PuTTY. Start PuTTY and put in the address of your host server to connect to on the first screen. In the menu on the left, pick 'Tunnels' from the tree. Under 'Add new forwarded port:' put in 1080 (this is pretty arbitrary, but 1080 is the "official" SOCKS port). Leave 'Destination' blank and choose the 'Dynamic' radio button. Feel free to go back to the 'Session' entry on the menu tree on the left if you wish to save a session so you don't have to do this every time.

2. Configure Firefox. Under Preferences, click the 'Connection Settings' button from the main 'General' options. Click 'Manual Proxy configuration:' and under 'SOCKS Host' put in localhost with port 1080. Click OK and try to surf. You should now be being routed through your Linux host. You can go to whatismyip.com to verify you're being routed through your host's IP address.

(I'm pasting this howto from one I wrote on another site)

SSH on port 443

[Anonymous Coward]

Another trick to get through corporate firewalls is to place your SSH server at home on port 443 - the HTTPS port.

Since both SSH and HTTPS use SSL, it is very hard for a corporate firewall to tell the difference, so often you can punch through in this way if your employer does not allow you to SSH out on the normal port.

Of course, by doing so you may be violating your company policies and opening yourself up to being fired - so don't blame me if you are.

Also, if you want to keep the script kiddies from trying to brute force your SSH server, run it on a non-standard port (to protect it from scripts) and turn OFF password authentication - force the use of a keypair to log in.

That last bit is important, so I will repeat it:

Turn OFF password authentication - force the use of a keypair to log in.

I'd've made that ALL CAPS if the lame filter (err, lameNESS filter) had let me.

Using a non-standard port is no subsitute for actually SECURING the server, but it does play a role in keeping the RiffRaff out - and after what Riff did to Frankie I don't want him in here.

(Posted anon since several people at work read Slashdot.)

Re:SSH on port 443

[mmogilvi]

And the easy way to do put ssh on port 443 is to put multiple "Port" lines in your /etc/sshd_config file on your server:

Port 22
Port 443

Then you can still access it on the standard port (22) when it isn't blocked by a firewall.

How about stunnel?

[syntax]

You might also look into stunnel. It acts more like a traditional daemon with conf file, and also has the neat feature of being able to turn any service into its standard ssl equivilent, if that exists, which is useful for things like imap/pop/http.