I've got two computers connected to the same router

  • Computer A runs Windows 10 Insider Preview. Insider Preview has VPN broken and can't be rolled back. :(
  • Computer B runs Linux Mint and has a VPN connection set up via openconnect.

Here's what ipconfig reports on B (fragment):

tun0      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:  P-t-P:  Mask:
          inet6 addr: fe80::7fb2:5598:b02e:e541/64 Scope:Link
          RX packets:24 errors:0 dropped:0 overruns:0 frame:0
          TX packets:42 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500 
          RX bytes:7005 (7.0 KB)  TX bytes:3243 (3.2 KB)

wlp3s0    Link encap:Ethernet  HWaddr 60:67:20:36:6f:a4  
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::8e96:7526:ff54:d1be/64 Scope:Link
          RX packets:22511502 errors:0 dropped:0 overruns:0 frame:0
          TX packets:16052631 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:24451442281 (24.4 GB)  TX bytes:6038264731 (6.0 GB)

I need to access resources behind VPN from computer A.

I'm thinking of configuring routes on A in such a way so that it would access VPN resources through B while using the router directly for everything else.

In the worst case, I can connect the two computers directly, but I would like to avoid that if possible.

On Windows, I can simply mark any adapter as shared. But when I do the same thing on Linux, the adapter loses connectivity. Not sure how to do that correctly.

  • 1
    Set routes for the remote nets (behind B) on A (as you already mentioned). You need to enable forwarding on wlp3s0 via sysctl and maybe iptables/firewall. Additionally you may need to NAT outgoing connections on tun0 onto If you get stuck, please update your question. – xx4h May 21 '18 at 20:26
  • I'm not familiar with iptables. I tried to follow this guide very carefully: techytalk.info/… But no luck. :( From computer A, I do a traceroute and see that it hits computer B for resources-behind-VPN, but can't ping them. :( – lolmaus - Andrey Mikhaylov May 22 '18 at 9:19
  • @xx4h Maybe if you expanded your comment to a full-fledged answer with enough detail, I'd be able to set it up, or at least tell exactly what's wrong. "Maybe some iptables" is not detailed enough for me. :( – lolmaus - Andrey Mikhaylov May 22 '18 at 9:20


On host A you need to route all traffic for the destination network to host B. I will assume this is something like

for linux (on host A):

ip r a via dev eth0

for windows (on host A):

route ADD MASK


After routing is in place, all packages for the network will be send to host B.

To allow packages to be forwarded from wlp3s0 to tun0 on host B, you need to enable IP forwarding.

To temporary enable IP forwarding for all interfaces:

sysctl net.ipv4.conf.all.forwarding=1

To enable this change permanently, add new line to /etc/sysctl.conf:

net.ipv4.conf.all.forwarding = 1

Additionally to interface settings, iptables could be active and need to allow package forwarding.

To check if iptables is active (at least for the FORWARD chain):

iptables -L FORWARD -nv

If the chain has no rules and the policy says ACCEPT, you are good to go, if not, you need to add relevant rules to allow forwarding for

Allow forwarding all packages to on wlp3s0:

iptables -I FORWARD -i wlp3s0 -d -j ACCEPT
iptables -I FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT

the RELATED,ESTABLISHED automatically allows the return packages.


Now, after forwarding is set up, packages will be send into the tunnel. But as far as the remote network behind the VPN does not know our local network, which is normally the case, we need to NAT all packages which come from our local network and will go into the VPN to the address, we got from the VPN-Server (which is the IP on the tun0).

To do this, you need to create a MASQUERADE rule in the POSTROUTING table:

iptables -t nat -I POSTROUTING -o tun0 -j MASQUERADE

This will nat all outgoing packages on tun0 to the interface`s IP.

  • 1
    It works! THANK YOU! tears of joy Likely, it's the FORWARD part that I was missing. PS Are you sure the sysctl directive is not net.ipv4.ip_forward? That's what other guides are saying. I used both. – lolmaus - Andrey Mikhaylov May 22 '18 at 12:23
  • 1
    Enabling net.ipv4.conf.all.forwarding will enable net.ipv4.ip_forward too. – xx4h May 22 '18 at 12:35
  • I seem to lose some of this configuration on every reboot. Can you please update the answer with a recommended way to make the configuration persistent? – lolmaus - Andrey Mikhaylov May 24 '18 at 9:09
  • The iptables rules will pass packets in wlp3s0 interface that are destined to But how they will be passed to tun0 interface? Dont you need a separate routing table entry for this? – Shiplu Mokaddim Sep 5 '18 at 17:49
  • 1
    Most of the time vpn servers push routes to the clients on connect connect. So, if the connection is successfully established from the client to the vpn server, the routes for the remote networks are in place. – xx4h Sep 5 '18 at 18:35

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