Linux @lemmy.ml shadowintheday2 @lemmy.world 3mo ago

Using RDP from Linux to Windows via Android and VPN

Ok I know this sounds crazy but it's all about Linux and iptables all the way

I'm using a rooted android phone as a VPN router to keep confidential traffic separated between networks

A and B are in the same network, B provides a separate network for C

Device A: Linux ip 192.168.15.32 wlan0 Device B: rooted Android phone with Termux and VPN Hotspot wlan0 ip 192.168.15.21 wlan1 ip 192.168.38.173

Device C: Windows 10 with RDP wlan1 ip 192.168.15.176

I've tried the following

A: sudo ip route add 192.168.38.0/24 via 192.168.15.21 dev enp1s0

B: Termux, su: sysctl -w net.ipv4.ip_forward=1


iptables -t nat -A POSTROUTING -s 192.168.38.0/24 -o wlan0 -j MASQUERADE

iptables -A FORWARD -i wlan0 -o wlan1 -s 192.168.15.0/24 -d 192.168.38.0/24 -j ACCEPT
iptables -A FORWARD -i wlan1 -o wlan0 -s 192.168.38.0/24 -d 192.168.15.0/24 -j ACCEPT

C: default route via 192.168.38.173 metric 1

C is solely seeing the internet from B's VPN, and can even access wlan0's router, meaning it has access to its internal network. C can ping B, B can ping C

B can ping A and C

A can ping B, but not C, which also means no RDP access

What am I missing ?

6 comments

I’d have to check my iptables syntax again but I’m not sure you want the FORWARD between the networks unless C has a manual route to get traffic for the 192.168.15.0/24 network back via B. You just want to NAT A behind B’s IP on 192.168.38.0/24. I think the forwards are sending the traffic without doing NAT on A.
- yes, but you really don't want to nat if you dont have to - gets too messy too quickly when direct IP connectivity is right there.
  
  @shadowintheday2@lemmy.world parent comment is correct. check routes on device C. make there is either a default route or a specific route back to A via B.
- how could I set up NAT like this ? thanks
Can you post ip r output.

Is your android being used as the modem/tether for device A? (If so adding route 192.168.38.0/24 via _gateway and _gateway dev x0 proto static scope link should allow it to reach C)

If using network manager just use the GUI to add the one line in routes. 192.168.38.0 24 yourgateway - it will do the metric on its own.

What are the gateway addresses?

You'd need to add a route from c to a as well, I believe, but I haven't used windows in forever.

(The above is what I've had to do to get a machine behind an android to ping my other devices.)
- ip r
  
  default via 192.168.15.1 dev enp3s0 proto dhcp src 192.168.15.32 metric 100 192.168.15.0/24 dev enp3s0 proto kernel scope link src 192.168.15.32 metric 100 192.168.38.0/24 via 192.168.15.21 dev enp3s0
so it seems that without any config, the traffic passes from wlan1 to wlan0's network flawlessly; but traffic from wlan0 network stops at the Android device, even with iptables -P FORWARD ACCEPT, so I'm clueless on what to do next

6 comments