Openvpn-netns

Run openvpn to configure network inside a network namespace so it can be used only by some applications.

The idea is that openvpn is run on the host, but puts the tun interface up inside the network namespace. The ip configuration will also be done in the namespace. For the dns, edit the the network namespace resolv.conf file stored in /etc/netns/NAMESPACENAME/resolv.conf.

I wrote this version after reading pekman/openvpn-netns

There was a lot of handling in the 'netns' script that I thought could be done with the --iproute option. Now only the 'resolv.conf' handling is kept as '--up' script.

https://discourse.nixos.org/t/run-systemd-service-in-network-namespace/3179/6 https://github.com/systemd/systemd/issues/2741 Many examples

Openvpn usage

sudo ip netns add vpnns
sudo openvpn \
    --setenv NETNS vpnns \
    --iproute ./openvpn-netns-ip \
    --up ./openvpn-netns-nameserver \
    --script-security 2 \
    --config vpn.conf
# Wait for the vpn to be configured

Checking

# In another terminal show that the vpn is working inside:
sudo ip netns exec vpnns ip route
default via 4.3.2.1 dev tun0
4.3.2.1/27 dev tun0 proto kernel scope link src 4.3.2.10

sudo ip netns exec vpnns cat /etc/resolv.conf
nameserver 4.3.2.1

sudo ip netns exec vpnns ping -c 3 9.9.9.9
PING 9.9.9.9 (9.9.9.9) 56(84) bytes of data.
64 bytes from 9.9.9.9: icmp_seq=1 ttl=60 time=185 ms
64 bytes from 9.9.9.9: icmp_seq=2 ttl=60 time=107 ms
64 bytes from 9.9.9.9: icmp_seq=3 ttl=60 time=163 ms

--- 9.9.9.9 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2001ms
rtt min/avg/max/mdev = 107.032/151.707/185.270/32.892 ms

# Traceroute goes through the vpn
sudo ip netns exec vpnns traceroute 9.9.9.9
traceroute to 9.9.9.9 (9.9.9.9), 30 hops max, 60 byte packets
 1  _gateway (4.3.2.1)  105.501 ms  105.840 ms  106.127 ms
 2  * * *
 3  * * *
 4  * * *
 5  dns9.quad9.net (9.9.9.9)  129.345 ms !X  49.028 ms !X  84.534 ms !X

Systemd integration

The systemd integration is made of different units for each functionnality:

• Creating the network namespace
• openvpn service to have vpn networking inside the namespace
  • Implemented as an 'override.conf' file
• Run the application inside the workspace
• Optional:
  • socat tcp redirection to access on the host a socket in the namespace

Implementation detail

A service creates the network namespace, and for simplicity, puts the loopback interface up. The application your want to run, uses this namespace using the NetworkNamespacePath=/var/run/netns/NETNSNAME option and binds to the netns unit.

Usage

• Put the 'services' files in '/usr/lib/systemd/system'
• Edit your 'openvpn-client@CONFIG.service' to use the network namespace
  • See 'templates/openvpn-netns.conf'
• Edit your service to use the network namespace
  • See 'templates/service-netns.conf'

Current state

• Openvpn configuration
• Create network namespace as a unit
• Provide "tcp port forwarding" to the namespace using socat
• Template to run a service inside the namespace
• Example for a service that runs 'transmission' with a 'transmission' namespace and vpn configuration.

Implementation

• openvpn uses an '--iproute' script to redirect all commands to the namespace. It also create the namespace for simplicity.
• The 'resolv.conf' file is handled by the '--up' script. 'domain/search' configuration is ignored as I do not need it.
• Network namespace configuration and port forwarding is done as separate units Putting the network up is still done at namespace creation for simplicity
• Forwarding of a TCP port is done using socat to not setup any extra v-eth

TODO

• Automation for testing?
• Documentation on how to test