[HOWTO] Tunneling the hard way: using slirp, pppd and socat

[mdeininger]

I couldn't find any Howtos on doing this dirty little heretic trick so i thought I'd share how I managed to do this in form of a howto in case someone else tries doing the same -- please don't flame me too much, this is probably my first "real" howto and I know it's pretty exotic a thing to do.

Contents

• 1. Preface / The Problem
  
• 2. Requirements
  
  
  
  • Hardware/Equipment
    
  • Software: slirp
    
  • Software: pppd
    
  • Software: socat
    
  
  
• 3. Configuring the Client
  
• 4. Configuring the Server
  
• 5. Optional: configuring your router
  
• 6. Testing
  
• 7. The odd scenario that worked for me
  
• 8. Possible extensions
  

1. Preface / The Problem
Every now and then you might come across a "bad" ISP. The one I have at home for example is dropping UDP packets ever so often when I try to play online games -- and it tends to drop random packets while I try to log onto a gameserver too which makes a certain game I like to play crash during the loading phase so it can't recover. I also heard of other ISPs blocking certain ports on external servers -- universities for example seem to like blocking p2p network ports and the school i was attending till last august blocked everything but port 80 for http -- including ftp which made even on-topic "research" a pita at times.
Usually there's three ways of working around this problem if "giving up" is not an option to you: a) change your ISP, b) use ssh to redirect ports, c) connect to an external VPN to route for you. a) can be tricky -- it's impossible if you're sharing the link with your parents and they insist on their email addresses or in the university/workplace/school scenario. b) will only work with single port/host combinations and for c) you will need a full-fledged rootbox idling around on the internet -- which tend to be expensive and "virtual servers" might not work because those often don't include tun/tap devices and/or kernel-level ppp support if you rent them and in case you rented them you probably can't fiddle around with its kernel to enable it (that was my problem at least). If any of this rings a bell to you, read on and discover method d)

NOTE: another application of this method is -- of course -- "anonymising". If you use this to route through a different box then you can't be traced that easily since the external box you will use in this example is effectively NATing your connection.

2. Requirements
Hardware/Equipment
As I said, this method is tricky and you do need quite some stuff to use it. You will need:

• Write-access to the routing tables and clearance to add interfaces with pppd on your client box (or your router and some other internal box) -- this means you need root-level access on linux
  
• Some external box with at least a shell account -- rootboxes are fine but a simple shell account somewhere will suffice ( yes, no root access on the host is required if you can get slirp and socat on it )
  

Software: slirp
Slirp is a SLIP/PPP emulator that was originaly intended to turn dial-in shell accounts into PPP-accounts. It's in portage and you can get it at http://slirp.sourceforge.net/. You will need this on the host box.
Software: pppd
This is the PPP client we will be using. You will already have this if you use PPPoE or a Modem to connect to the internet on your client box. It's also in portage as "net-dialup/ppp" and it should be available for download at http://www.samba.org/ppp. You will need this on the client box.
Software: socat
According to it's website it's "netcat++", and I also read references to it of the form "socat is netcat on steroids" -- and that's completely true. It's the "enhanced swiss army knife" of a netadmin since you can do just about anything with it, including things like creating a wannabe-telnet server (example included in socats manpage). It's in portage and you can get it from http://www.dest-unreach.org/socat/. You will need this on both the client and the server and we will use it to establish bidirectional tcp/ip connection between the two instead of a modem.

3. Configuring the client
Okay now that we know what is needed, let's get our hands dirty. Since this is the client, you will need to install pppd and socat on this box. Also I will assume both of the boxes to use gentoo for installation instructions since I think installing those three programs -- even from source tarballs [untar; ./configure; make; make install] -- should be easy enough if you're not running gentoo. If you haven't done so already, use

[frozenJim]

You have Ryzom running?!!

Please, tell me more.... What did you do to get it going? Can a dummy like me play ryzom on my Gentoo box?
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Who controls the past, controls the future. Who controls the present, controls the past.

[mdeininger]

uhm, nothing spectacular, the first time i tried it just ran right out of the box; something broke while patching then though, so last time i gave that a shot i just followed this guide on the official forums, substituting cedega with wine:
http://www.ryzom.com/forum/showthread.php?t=8887

it's a bit slow on ati cards though, albeit it seems to run fine on my shiny new geforce... you will need more ram than on windows though

aside from that i see no reason why it shouldn't work on a gentoo box, the engine actually runs on linux and the devs did a good job in making the program portable
_________________
"Confident, lazy, cocky, dead." -- Felix Jongleur, Otherland

( Twitter | Blog | GitHub )

[frozenJim]

Oh. That's my mistake. I thought that there was a Linux version (now I cannot remember why I thought that).

Well, to heck with them then.

My need to play is not so great as my need to avoid rewarding companies who shun Linux.
_________________
Who controls the past, controls the future. Who controls the present, controls the past.

[mdeininger]

well, they originally wanted to make a Linux version, which is why they GPL'd the engine and it also compiles on Linux. They also use Debian-servers, however they didn't get around to port the actual game to Linux, because the devs were busy with the game for windows due to marketing problems (You will notice that Ryzom has a very small user-base). I'm only playing every once in a while, but I felt like supporting specifically them because they're the closest you can get to see a commercial MMORPG on anything but windows (except for WoW on OSX that is) and I found it quite nice that they GPL'd the engine.
_________________
"Confident, lazy, cocky, dead." -- Felix Jongleur, Otherland

( Twitter | Blog | GitHub )

[frozenJim]

Ah. Well then, I take back my ingracious comments.

Good on'em I say!

So now it's just a matter of someone actually writing a game that utilizes the engine. The ball is in our court.

You would think though, that they would benefit from having the Linux crowd joining up on their servers. With the engine already written, wouldn't you think that it would be pretty straightforward for the authors to create a Linux port and then cash in on all of us starving Linux gamers?

Better for all if both Linux and Micro$oft gamers could play together on the same server.
_________________
Who controls the past, controls the future. Who controls the present, controls the past.

[mdeininger]

that's true and I feel the same. I think there's also a petition on the official forums, but the thing is they're still working on the game's features, and something is wrong with the native linux audio drivers. It's definitely possible, but I think the game has a reputation of being a more "girly" one, and it seems the majority of users either plays on windows or doesn't have any trouble running it on wine whatsoever, except for some performance issues... If I got it right, they're also quite tight on developers, up until last month they were working on a major game enhancement, so maybe they'll look into it sometime soon
_________________
"Confident, lazy, cocky, dead." -- Felix Jongleur, Otherland

( Twitter | Blog | GitHub )

[frozenJim]

Maybe what we need is some kind of "Linux Gaming Foundation" that is devoted to generating the money that is required for these technically challenging apps on a game-by-game basis.

Games are not like a spreadsheet or a wordprocessor, they cannot be put out a piece at a time and they have to be written FAST by a group dedicated to just one game. 3D immersive games require a huge pool of expertise in the API of that particular game and so it has to be a full-time job if you are to be effective. Look at FreeCiv and you will see how a game fares under the current model (I LIKE freeciv - but it has no polish and will never be popular enough to challenge Sid Meier's work).

I don't see the game vendors helping out much because they have nothing to gain. But the MMORPG world has a lot to gain. Linux folk are the group best suited to taking an online game and improving the living CRAP out of it. I have long suspected that those types who are attracted to Linux may be the ones who prefer the virtual worlds of MMORPG.

Perhaps EverQuest could benefit from opensourcing AND providing some monetary incentives to developers of an Everquest version on Linux. We would still be paying monthly for the service, but breaking no rules of the GPL.

Has anyone looked into this?
_________________
Who controls the past, controls the future. Who controls the present, controls the past.

[jtheisen]

I'd like to add that in when I tried it, I had to explicitly set IP addresses for ppp by putting the line