Accidental routing loop



  • I'm on a network with one gateway and one windows pc on the lan.  I wanted to test OpenVPN so I VPNed to the gateway, using default server.conf.  This works fine.

    Then I configured server.conf to push the LAN subnet to the client.  After vpning in a second time I couldn't ping either the VPN subnet or LAN subnet.  Routing loop.

    (LAN)        (VPN)    (loopback)    (LAN)
    10.11.12.0 -> 10.8.0.6 -> 127.0.0.0 -> 10.11.12.0

    What I don't understand is how the loopback interface, 127.0.0.0/8 points to the LAN interface.

    I know the loopback gets to the LAN interface somehow because the first time I connected and 10.8.0.6 pointed to 127.0.0.1 my gateway was receiving pings.

    windows route print:

    
    Active Routes:
    Network Destination        Netmask          Gateway       Interface  Metric
              0.0.0.0          0.0.0.0       10.11.12.1    10.11.12.254       10
             10.8.0.1  255.255.255.255         10.8.0.5        10.8.0.6       1
             10.8.0.4  255.255.255.252         10.8.0.6        10.8.0.6       30
             10.8.0.6  255.255.255.255        127.0.0.1       127.0.0.1       30
           10.11.12.0    255.255.255.0     10.11.12.254    10.11.12.254       10
           10.11.12.0    255.255.255.0         10.8.0.5        10.8.0.6       1
         10.11.12.254  255.255.255.255        127.0.0.1       127.0.0.1       10
       10.255.255.255  255.255.255.255         10.8.0.6        10.8.0.6       30
       10.255.255.255  255.255.255.255     10.11.12.254    10.11.12.254       10
            127.0.0.0        255.0.0.0        127.0.0.1       127.0.0.1       1
        189.25.78.113  255.255.255.255       10.11.12.1    10.11.12.254       10
            224.0.0.0        240.0.0.0         10.8.0.6        10.8.0.6       30
            224.0.0.0        240.0.0.0     10.11.12.254    10.11.12.254       10
      255.255.255.255  255.255.255.255         10.8.0.6        10.8.0.6       1
      255.255.255.255  255.255.255.255     10.11.12.254    10.11.12.254       1
    Default Gateway:        10.11.12.1
    
    

    To fix the routing loop I can just push a separate subnet.


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