this post was submitted on 04 Oct 2024
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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 ?

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[–] masterofn001@lemmy.ca 3 points 1 day ago* (last edited 1 day ago) (1 children)

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.)

[–] shadowintheday2@lemmy.world 2 points 9 hours ago* (last edited 9 hours ago)

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    
[–] CondorWonder@lemmy.ca 4 points 1 day ago (2 children)

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.

[–] shadowintheday2@lemmy.world 1 points 9 hours ago

how could I set up NAT like this ? thanks

[–] qprimed@lemmy.ml 2 points 1 day ago* (last edited 1 day ago)

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.