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Accidental routing loop

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Join Date: Oct 2008

Posts: 46

Reputation: shwick is an unknown quantity at this point

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shwick

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Accidental routing loop

Nov 6th, 2008

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:

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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.