title: 'network_mode' and 'networks' cannot be combined workaround
body: <p>I am currently using <a href="https://www.tinc-vpn.org/documentation/tincd.8" rel="noreferrer">tinc</a> to create a VPN between two servers. This allows me from server A to access B through the IP address <code>10.0.0.2</code> and creates an interface:</p>
  
  <pre><code>tun0: flags=4305&lt;UP,POINTOPOINT,RUNNING,NOARP,MULTICAST&gt;  mtu 1500
          inet 10.0.0.1  netmask 255.255.255.0  destination 10.0.0.1
          inet6 fe80::babb:cc53:dd5e:23f8  prefixlen 64  scopeid 0x20&lt;link&gt;
          unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 500  (UNSPEC)
          RX packets 42  bytes 11987 (11.7 KiB)
          RX errors 0  dropped 0  overruns 0  frame 0
          TX packets 55  bytes 7297 (7.1 KiB)
          TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
  </code></pre>
  
  <p>I would like to pass this <em>route</em> to my docker container on server A:</p>
  
  <pre><code>version: '3.2'
  services:
    traefik:
      image: "traefik:v2.2.0"
      ports:
        - "80:80"
        - "443:443"
      volumes:
        - "/var/run/docker.sock:/var/run/docker.sock:ro"
        - "./acme:/acme"
        - "./traefik.toml:/traefik.toml"
        - "./rules:/etc/traefik/rules"
      networks:
        - traefik
      deploy:
        placement:
          constraints:
            - node.role == manager
  
  networks:
    traefik:
      external: true
  </code></pre>
  
  <p><sub>
  Currently inside the container <code>traefik</code> I can <code>ping 10.0.0.2</code> but it is a different host completely.
  </sub></p>
  
  <p>If I remove:</p>
  
  <pre><code>networks:
    traefik:
      external: true
  </code></pre>
  
  <p>and add <code>network_mode: host</code> within the <code>traefik</code> service I can route to <code>10.0.02</code> but then I cannot access other containers which share the <code>traefik</code> network. </p>
  
  <p>If I try and put them both together I get the error:</p>
  
  <blockquote>
    <p>'network_mode' and 'networks' cannot be combined</p>
  </blockquote>
  
  <hr>
  
  <p>In other words how can I create the dashed line connection?</p>
  
  <p><a href="https://i.stack.imgur.com/f3XbY.png" rel="noreferrer"><img src="https://i.stack.imgur.com/f3XbY.png" alt="enter image description here"></a></p>
  
  <p>This also depicts my problem in that <code>container B</code> can't be in both networks at once. </p>
  
  <p><a href="https://i.stack.imgur.com/ckkFY.png" rel="noreferrer"><img src="https://i.stack.imgur.com/ckkFY.png" alt="enter image description here"></a></p>
  
  <p><sub>I added <code>Server A</code> just as a more real world example of a swarm.</sub></p>