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how must a routetable be configured to use openvpn tunnel?
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skorefish
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Joined: 21 Jun 2015
Posts: 277

PostPosted: Tue Feb 02, 2016 3:59 pm    Post subject: how must a routetable be configured to use openvpn tunnel? Reply with quote

hey,

I can't figure out how the Kernel ip routing table must look like, to use an openvpn tunnel.
Can someone give me an example of this?
Code:

tunnel started

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
0.0.0.0         192.168.2.1     0.0.0.0         UG        0 0          0 enp5s1
10.100.0.1      10.100.0.5      255.255.255.255 UGH       0 0          0 tun0
10.100.0.5      0.0.0.0         255.255.255.255 UH        0 0          0 tun0
127.0.0.0       0.0.0.0         255.0.0.0       U         0 0          0 lo
192.168.2.0     0.0.0.0         255.255.255.0   U         0 0          0 enp5s1

before tunnel

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
0.0.0.0         192.168.2.1     0.0.0.0         UG        0 0          0 enp5s1
127.0.0.0       0.0.0.0         255.0.0.0       U         0 0          0 lo
192.168.2.0     0.0.0.0         255.255.255.0   U         0 0          0 enp5s1
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szatox
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Joined: 27 Aug 2013
Posts: 1717

PostPosted: Tue Feb 02, 2016 4:36 pm    Post subject: Reply with quote

So... You are inside network with IP 192.168.2/24 and you want to use tunnel 10.100.0.0/something.
First thing, one of the endpoints needs public IP (say, it's the other host) and VPN IP (10.100.0.1).

Code:
Kernel IP routing table
Destination             Gateway         Genmask         Iface
<remote public IP> 192.168.2.1         255.255.255.255   enp5s1 # route traffic to the other endpoint via your external NIC
0.0.0.0             10.100.0.1         0.0.0.0           tun0 # route everything else through the tunnel


Skipping other entries as they are irrelevant from the perspective of setting up a tunnel.
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skorefish
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Joined: 21 Jun 2015
Posts: 277

PostPosted: Tue Feb 02, 2016 5:20 pm    Post subject: Reply with quote

Code:

route add  -net 192.168.2.99  netmask 255.255.255.255 gw 192.168.2.1  dev enp5s1

works
 
route add  -net 0.0.0.0  netmask 0.0.0.0 gw 10.100.0.1  dev tun0
SIOCADDRT: Network is unreachable

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
0.0.0.0         192.168.2.1     0.0.0.0         UG        0 0          0 enp5s1
10.100.0.1      10.100.0.5      255.255.255.255 UGH       0 0          0 tun0
10.100.0.5      0.0.0.0         255.255.255.255 UH        0 0          0 tun0
127.0.0.0       0.0.0.0         255.0.0.0       U         0 0          0 lo
192.168.2.0     0.0.0.0         255.255.255.0   U         0 0          0 enp5s1
192.168.2.99    192.168.2.1     255.255.255.255 UGH       0 0          0 enp5s1
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