VTun - Frequently Asked Questions

1. General Questions
1.1 What is VTun ?
VTun is the easiest way to create Virtual Tunnels over TCP/IP networks
with traffic shaping, compression, and encryption. 
It supports IP, PPP, SLIP, Ethernet and other tunnel types.
VTun is easily and highly configurable, it can be used for various
network tasks.

1.2 What does VTun stand for ?
Virtual TUNnel.

1.3 Whom do I contact for support ?
Please send your suggestions, questions and problem descriptions to
VTun mailing list vtun@office.satix.net

1.4 Is VTun Y2K compliant?
YES.

1.5 Where can I download VTun package ?
You can download complete VTun package from the following web sites:
Primary:
  http://vtun.sourceforge.net
Mirrors:
  http://vtun.saol.com
  http://vtun.speedway.net
  http://vtun.euronet.be

1.6 Can I establish VTun tunnel with Windows machine ?
Unfortunately there is no VTun client for Windows yet.
We a looking for a guru who will port VTun to Windows.

1.7 Can I establish VTun tunnel with Cisco ?
No. VTun doesn't support tunneling with Cisco.

1.8 Does VTun support PPTP, L2TP, IPsec ?
VTun uses it's own simple and efficient protocol with TCP or UDP.
It doesn't support PPTP, L2TP, IPsec.

1.9 What platforms are supported by VTun ?
VTun was developed on Linux and then ported to several other OS:
   Linux (any glibc based distribution)
   Solaris
   FreeBSD, OpenBSD, NetBSD and other BSD clones.

1.10 Does VTun server support multiple clients ?
Sure. Number of the clients is limited only by the capabilities of 
your machine.

1.11 How many tunnels can VTun handle ?
Number of the tunnels is limited only by the capabilities of your
machine.

1.12 What do I need to run VTun ?
You should install and configure VTun package and read documentation.
Usually you'll need: 
   Universal TUN/TAP device driver (http://vtun.sourceforge.net/tun)
   PPP driver and pppd.

1.13 What hardware do I need to run VTun ?
Hardware requirements depends on your configuration:
   486DX2/66/16Mb will handle simple tunnels without compression 
   and encryption.
   P200/64Mb will handle several medium speed tunnels with compression 
   and encryption without any problem.
   Celeron 400/64Mb, perfectly encrypts and compresses high speed
   channels like 2Mbits.
Real life examples:
   PII466/128Mb was compressing several 3-4Mbits tunnels.  
   AlphaXL 266/64Mb was compressing and shaping about 10-50 tunnels 
   from 64Kbit to 512Kbit.
   P200MMX/64Mb with about 100 tunnels over loopback.

1.14 VTun supports many tunnel types, which type should I use ?
Well, it is not very easy to answer this question in the FAQ.
Please read documentation which comes with VTun package and visit 
VTun web site http://vtun.sourceforge.net

1.15 Where can I find configuration recommendations and examples ?
VTun package contains several config file samples.
Please read README.Setup

1.16 Why ZLIB compression does not work with UDP protocol ?
UDP doesn't not provide reliable transport, and some frames could be 
lost on unreliable links. VTun does not have any retransmition or 
recovery algorithm for the lost UDP frames, because retransmition will
be handled by Upper layers.
You should use LZO compression with UDP protocol.    

1.17 Why PPP tunnel is unstable over UDP ?  
Explanation is the same as with above case. Use TCP for PPP tunnels or 
use TUN instead of PPP, since tun device is completely the same with 
ppp device for the kernel. 

1.18 Why do routes specified after 'ppp' command in config file produce errors and don't install correctly ?  
Actually there is no straight way to determine when pppd has established 
connection with the other end. VTun execute those route commands right 
after the launch of pppd and if PPP link is not established, route 
commands will fail. Since version 2.0b3, VTun delays 10 seconds before 
issuing the route commands, which should fix almost all cases.  
I'll think about more elegant way to fix this problem.

1.19 How secure is VTun ?
Well. VTun doesn't try to be the MOST secure tunneling software in the 
world, it tries to be fast, stable, rich of features, easy to use 
and secure enough instead.
VTun uses Challenge Based Authentication and doesn't transfer passwords 
in clear text. Encryption module uses MD5 for 128 bits key generation 
and BlowFish algorithm for actual data encryption.
There could be some weaknesses in key generation method, we will try 
to address them in future releases. 

1.20 Who has developed so nice and cool software ?
Thanks :). You can find list of VTun team members on the web site or
in the 'Credits' file in VTun package.  

1.21 I don't like VTun where can I send complains ?
You can send them to /dev/null. 

1.22 Where can I get more information about VTun ?
VTun package contains: 
   Manual page for vtund.
   Manual page for configuration file.
   Fully documented config file.
   Several README files.

1.23 Can I use vtun over SSH ?
Yes, via the port forwarding feature of ssh.  Don't enable vtun's
encryption as ssh does its own encryption.  Also, make sure to select
the tcp protocol as SSH can forward tcp but not udp.  An example
session might look something like this:

home$ ssh -L 5000:localhost:5000 work.megacorp.com
(authenticate if necessary)
work$ vtund -s home_tunnel_config
...
home$ vtund home_tunnel_config localhost

1.24 Is it possible to establish a vtun link from a client behind NAT or a firewall?
Yes it is, but you need to use TCP protocol.

2. Error Messages
2.1 Why do I see no vtund log and error messages ?
On several Unices, FreeBSD for example, syslog doesn't log message 
with INFO priority, by default. 
You should add "*.info;" to the line with /var/log/messages in 
/etc/syslog.conf.

2.2 Why do I get "Input/output error" pppd error message ?
This usually means that vtund on other side has dropped connection,
check logs on other side.

2.3 Why do I get "couldn't find any suitable secret (password)" pppd error message ?
New versions of pppd use authentication by default.
Just add "noauth" option to ppp command.

2.4 Why do I get "XXXX returned error Y" error message ?
Usually this means that you use incorrect syntax for that command.
Also please read question 1.19 about routes and pppd.

2.5 Why do I get "Serial line is looped back" pppd error message ?
Sometimes pppd incorrectly decides that pseudo terminal is looped back. 
Just add "nomagic" option to ppp command.

2.6 Why do I get "Can't allocate tun device" or "Can't allocate tap device" error messages ?
This error means that Universal TUN/TAP driver module is not loaded
or you do not have correct /dev/tunXX or /dev/tapXX device nodes.
Make sure you have installed and configured Universal TUN/TAP device
driver (http://vtun.sourceforge.net/tun)

2.7 Why do I get "LZO compression is not supported" error message ?
This error means that LZO compression is not compiled in.
You will have to download binary VTun package or recompile vtund with
LZO support.

2.8 Why do I get "expecting WORD at line xxx" error message ?
This usually means that you are using a password that contain only
numerical characters.
VTun passwords must be alpha characters or a mixture of alpha and
numerical characters.

If you have any unanswered question please send it to the mailing list 
vtun-users@lists.sourceforge.net
