tunnel-server

A Linux GRETAP tunnel server & client

Usage

On the server:

sudo server/server.py --bridge br0 eth0

Here eth0 is the interface to listen for connections on and to route tunnel traffic over.

On the client:

sudo client/client.py <IP address of server>

What this does

This creates a GRETAP tunnel between the client and the server. At either end of the tunnel, the resulting GRETAP interface can be attached to a bridge by specifying --bridge <bridge-name>.

No attempt is made to monitor the connection or keep it alive.

What this DOES NOT do

This is not a VPN. If you want a VPN, use a VPN. This gives you a virtual layer 2 connection between two hosts, nothing more. It implements no authentication, no authorisation and no encryption.

Why would I want this?

I use this over a layer 3 VPN. That is, a VPN which can route IP traffic from one host to another. A layer 3 VPN is useless if you are testing Ethernet equipment because Ethernet is a layer 2 protocol and you can't create an Ethernet connection over a layer 3 VPN. So a layer 2 tunnel over the top of the VPN gives you a virtual "Ethernet" connection between two hosts that don't have a real (direct) Ethernet connection but can talk to each other by IP.

There are generally three ways of using this:

• Point to Point By default, it just creates a GRETAP interface at each end of the tunnel. You are responsible for whatever configuration you want on top of that.
• Join a remote network In this mode, you are responsible for creating a network bridge at one end, let's say it's called br0. At that end of the tunnel, you specify --bridge br0 on the command line. That end of the tunnel will be added to the bridge you specify. Suppose that bridge also has an Ethernet interface slaved to it which is on an office network; now the other end of the tunnel can use its GRETAP interface as though it was a real Ethernet interface plugged into that remote network (hint: start a DHCP client on the remote end and it'll get an IP address from the office network's DHCP server. IP6 link local addresses will also work over it).
• Join two networks In this mode, create a bridge at both ends of the tunnel and specify --bridge br0 at both ends. This lets you join two remote networks into a single layer 2 broadcast domain, effectively joining them into a single Ethernet network. Be careful doing this. If you bridge your office network onto your home network and your home DHCP server starts serving up IP addresses for your office network, your IT guy is not likely to be impressed.

And let's say this one more time

THIS IS NOT A VPN. Don't use this over the internet unless you are sure the traffic it's carrying could also be carried safely over the internet. If you're not sure, set up a VPN first (eg OpenVPN) and then start this through the VPN connection.