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I am currently trying to route all incoming and outgoing network traffic to/from applications listening on an OpenVPN tunnel tun1 through said tunnel.

Here are my devices: tun0 is an OpenVPN server running on the machine that provides access to the machine's local network to remote machines. tun1 is an OpenVPN client to a remote server.

# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:1c:c0:d7:98:1c  
          inet addr:192.168.178.9  Bcast:192.168.178.255  Mask:255.255.255.0
          inet6 addr: fe80::21c:c0ff:fed7:981c/64 Scope:Link
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
          RX packets:103987444 errors:0 dropped:0 overruns:0 frame:0
          TX packets:161412265 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:583178850 (556.1 MiB)  TX bytes:1006632339 (959.9 MiB)
          Interrupt:43 Base address:0x8000 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:505197 errors:0 dropped:0 overruns:0 frame:0
          TX packets:505197 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:91836367 (87.5 MiB)  TX bytes:91836367 (87.5 MiB)

tun0      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:10.9.8.1  P-t-P:10.9.8.2  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
          RX packets:4 errors:0 dropped:0 overruns:0 frame:0
          TX packets:4 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:272 (272.0 B)  TX bytes:960 (960.0 B)

tun1      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:10.8.0.10  P-t-P:10.8.0.9  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
          RX packets:7 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:588 (588.0 B)  TX bytes:588 (588.0 B)

Here are the currently active routes:

# ip route show table main
default via 192.168.178.1 dev eth0 
10.8.0.1 via 10.8.0.9 dev tun1 
10.8.0.9 dev tun1  proto kernel  scope link  src 10.8.0.10 
10.9.8.0/24 via 10.9.8.2 dev tun0 
10.9.8.2 dev tun0  proto kernel  scope link  src 10.9.8.1 
192.168.178.0/24 dev eth0  proto kernel  scope link  src 192.168.178.9 

After some research, I learned that I had to use "policy routing" to direct all traffic on tun1 through another gateway (10.8.0.1). So I created a new table "tun1" and tried to configure it.

# echo "1 tun1tbl" >> /etc/iproute2/rt_tables
# ip route add 10.8.0.0/24 dev tun1 src 10.8.0.10 table tun1tbl
# ip route add default via 10.8.0.1 dev tun1 table tun1tbl
RTNETLINK answers: No such process

Why can't I set the default route for this device/table?

-- edit: I just found another potential solution, using only route, but it fails with a similar error:

# route add default gw 10.8.0.1 dev tun1
SIOCADDRT: No such process

1 Answer 1

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In your command, you request to send packets via tun1 via the next hop 10.8.0.1:

ip route add default via 10.8.0.1 dev tun1 table tun1tbl

But this network interface is not on a subnet, which would contain the target address:

tun1      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:10.8.0.10  P-t-P:10.8.0.9  Mask:255.255.255.255

Thus the commands refuse to add such route.

As tun1 is a point-to-point interface, you do not need a gateway to send out packets. Just remove the via part from your command:

ip route add default dev tun1 table tun1tbl

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