share-ipv4-with-ipv6-tunnel.txt

share ipv4 network with ipv6 tunnel
===

# Case
```
                 <ipv6-tunnel>                <general ipv4 network>
[My device (M)] =============== [Server (S)] ------------------------ [ ipv4, 0/0 ]
            eth0:             :eth0        :usb0
```
where
	M : (as client)
		ipv4 not avaliable
		ipv6 avaliable
		ipv6 : [e::e/64] dev eth0

	S : (as server)
		both ipv4 and ipv6 avaliable
		ipv6 : [e::1/64] dev eth0
		ipv4 : [192.168.x.x] dev usb0

purpose :
	share Server's ipv4 access with My device, via an ipv6 tunnel between M and S.

# Prepare @ M
	* setting up tunnel at client
		$ ip -6 tunnel add name gre1v6 mode ip6gre remote e::1 local e::e dev eth0
	* add an IP address for dev gre1v6
		$ ip addr add 10.0.0.2/8 brd + dev gre1v6
	* turn on dev gre1v6
		$ ip link set dev gre1v6 up
	* setup route
		$ ip route add to 0/0 via 10.0.0.1 dev gre1v6
		(no need to touch ipv6 route in this case)

	hint) to check them :
		$ ip [-6] addr
		$ ip [-6] route
		$ ip [-6] tunnel

# Prepare @ S
	* setting up tunnel at server
		$ ip -6 tunnel add name gre1v6 mode ip6gre remove e::e local e::1 dev eth0
	* add IP addr for dev gre1v6
		$ ip addr add 10.0.0.1/8 brd + dev gre1v6
	* turn on gre1v6
		$ ip link set dev gre1v6 up
	* route (default)
	* enable kernel :: net.ipv4.ip_forward
		$ sysctl net.ipv4.ip_forward=1
	* setup ipv4 NAT
		$ iptables -t nat -I POSTROUTING -o usb0 -j MASQUERADE
	
# Communication Test
1) tunnel test
	@M :
		* ipv6
			ping6 e::1[%eth0]
		* ipv4 in v6tunnel
			ping 10.0.0.1
	@S :
		* ipv6
			ping6 e::e[%eth0]
		* ipv4 in v6tunnel
			ping 10.0.0.2
	if all passed, the tunnel is ready to work.

2) final test
	@M :
		ping <some-IP-that-is-outside> [-I gre1v6]
	@S :
		iptables -t nat -nvL # to see if there is any packets transfered.