i want to use my computer as gateway, all traffic must use vpn

malf

3/19/24, 8:36 PM

this is my configuration

i got 2 computers with ubuntu 22

computer1 with internet and vpn:

eth0 192.168.10.100
eth1 192.168.20.100
tun0 10.33.12.19

now computer2 must use internet by vpn of computer1:

eth0 192.168.20.200

the connection between computer1 and computer2 by 192.168.20.0/24

computer1 enabling forwarding with sudo sh -c "echo 1 > /proc/sys/net/ipv4/ip_forward"

iptables -t nat -A POSTROUTING -o tun+ -j MASQUERADE
iptables -A FORWARD -i eth1 -o tun+ -j ACCEPT
iptables -A FORWARD -o tun+ -j ACCEPT
iptables -A FORWARD -i tun+ -m conntrack --ctstate ESTABLISHED,RELATED   -j ACCEPT
iptables -A INPUT -i tun+ -j ACCEPT

now testing the connection

host google.com on computer2 generate 2 queries with 2 answers

computer1:

tcpdump -i any -n port 53
20:51:27.210377 eth1  In  IP 192.168.20.100.57730 > 178.162.209.143.53: 31575+ A? google.com. (28)
20:51:27.210435 tun0  Out IP 10.33.12.19.57730 > 178.162.209.143.53: 31575+ A? google.com. (28)
20:51:27.219631 tun0  In  IP 178.162.209.143.53 > 10.33.12.19.57730: 31575 1/0/0 A 142.250.184.206 (44)
20:51:27.219666 tun0  Out IP 178.162.209.143.53 > 192.168.20.100.57730: 31575 1/0/0 A 142.250.184.206 (44)

one answer direct and one answer thru vpn but only the direct answer reach computer2

all traffic must use vpn, so delete direct routing on computer1 with

ip route del 192.168.20.0/24
dev eth1 proto kernel scope link src 192.168.20.200

if i repeat on computer2 the query dns with host google.com, there is still the answer on computer1, but the answer does not reach computer2

what is the routing for vpn answer ?

perhaps my configuration is bad and there is another configuration ?

0 + 1

configuration

vpn

routing

gateway

Doug Smythies

3/20/24, 3:20 PM

Your tcpdump capture looks correct.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: i want to use my computer as gateway, all traffic must use vpn

Post an answer

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