mirror of
git://anongit.mindrot.org/openssh.git
synced 2024-11-24 19:53:24 +08:00
133 lines
4.8 KiB
Plaintext
133 lines
4.8 KiB
Plaintext
How to use OpenSSH-based virtual private networks
|
|
-------------------------------------------------
|
|
|
|
OpenSSH contains support for VPN tunneling using the tun(4) network
|
|
tunnel pseudo-device which is available on most platforms, either for
|
|
layer 2 or 3 traffic.
|
|
|
|
The following brief instructions on how to use this feature use
|
|
a network configuration specific to the OpenBSD operating system.
|
|
|
|
(1) Server: Enable support for SSH tunneling
|
|
|
|
To enable the ssh server to accept tunnel requests from the client, you
|
|
have to add the following option to the ssh server configuration file
|
|
(/etc/ssh/sshd_config):
|
|
|
|
PermitTunnel yes
|
|
|
|
Restart the server or send the hangup signal (SIGHUP) to let the server
|
|
reread it's configuration.
|
|
|
|
(2) Server: Restrict client access and assign the tunnel
|
|
|
|
The OpenSSH server simply uses the file /root/.ssh/authorized_keys to
|
|
restrict the client to connect to a specified tunnel and to
|
|
automatically start the related interface configuration command. These
|
|
settings are optional but recommended:
|
|
|
|
tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... reyk@openbsd.org
|
|
|
|
(3) Client: Configure the local network tunnel interface
|
|
|
|
Use the hostname.if(5) interface-specific configuration file to set up
|
|
the network tunnel configuration with OpenBSD. For example, use the
|
|
following configuration in /etc/hostname.tun0 to set up the layer 3
|
|
tunnel on the client:
|
|
|
|
inet 192.168.5.1 255.255.255.252 192.168.5.2
|
|
|
|
OpenBSD also supports layer 2 tunneling over the tun device by adding
|
|
the link0 flag:
|
|
|
|
inet 192.168.1.78 255.255.255.0 192.168.1.255 link0
|
|
|
|
Layer 2 tunnels can be used in combination with an Ethernet bridge(4)
|
|
interface, like the following example for /etc/bridgename.bridge0:
|
|
|
|
add tun0
|
|
add sis0
|
|
up
|
|
|
|
(4) Client: Configure the OpenSSH client
|
|
|
|
To establish tunnel forwarding for connections to a specified
|
|
remote host by default, use the following ssh client configuration for
|
|
the privileged user (in /root/.ssh/config):
|
|
|
|
Host sshgateway
|
|
Tunnel yes
|
|
TunnelDevice 0:any
|
|
PermitLocalCommand yes
|
|
LocalCommand sh /etc/netstart tun0
|
|
|
|
A more complicated configuration is possible to establish a tunnel to
|
|
a remote host which is not directly accessible by the client.
|
|
The following example describes a client configuration to connect to
|
|
the remote host over two ssh hops in between. It uses the OpenSSH
|
|
ProxyCommand in combination with the nc(1) program to forward the final
|
|
ssh tunnel destination over multiple ssh sessions.
|
|
|
|
Host access.somewhere.net
|
|
User puffy
|
|
Host dmzgw
|
|
User puffy
|
|
ProxyCommand ssh access.somewhere.net nc dmzgw 22
|
|
Host sshgateway
|
|
Tunnel Ethernet
|
|
TunnelDevice 0:any
|
|
PermitLocalCommand yes
|
|
LocalCommand sh /etc/netstart tun0
|
|
ProxyCommand ssh dmzgw nc sshgateway 22
|
|
|
|
The following network plan illustrates the previous configuration in
|
|
combination with layer 2 tunneling and Ethernet bridging.
|
|
|
|
+--------+ ( ) +----------------------+
|
|
| Client |------( Internet )-----| access.somewhere.net |
|
|
+--------+ ( ) +----------------------+
|
|
: 192.168.1.78 |
|
|
:............................. +-------+
|
|
Forwarded ssh connection : | dmzgw |
|
|
Layer 2 tunnel : +-------+
|
|
: |
|
|
: |
|
|
: +------------+
|
|
:......| sshgateway |
|
|
| +------------+
|
|
--- real connection Bridge -> | +----------+
|
|
... "virtual connection" [ X ]--------| somehost |
|
|
[X] switch +----------+
|
|
192.168.1.25
|
|
|
|
(5) Client: Connect to the server and establish the tunnel
|
|
|
|
Finally connect to the OpenSSH server to establish the tunnel by using
|
|
the following command:
|
|
|
|
ssh sshgateway
|
|
|
|
It is also possible to tell the client to fork into the background after
|
|
the connection has been successfully established:
|
|
|
|
ssh -f sshgateway true
|
|
|
|
Without the ssh configuration done in step (4), it is also possible
|
|
to use the following command lines:
|
|
|
|
ssh -fw 0:1 sshgateway true
|
|
ifconfig tun0 192.168.5.1 192.168.5.2 netmask 255.255.255.252
|
|
|
|
Using OpenSSH tunnel forwarding is a simple way to establish secure
|
|
and ad hoc virtual private networks. Possible fields of application
|
|
could be wireless networks or administrative VPN tunnels.
|
|
|
|
Nevertheless, ssh tunneling requires some packet header overhead and
|
|
runs on top of TCP. It is still suggested to use the IP Security
|
|
Protocol (IPSec) for robust and permanent VPN connections and to
|
|
interconnect corporate networks.
|
|
|
|
Reyk Floeter
|
|
|
|
$OpenBSD: README.tun,v 1.4 2006/03/28 00:12:31 deraadt Exp $
|