SIOCSIFNETMASK: Invalid argument using OpenVPN on Ubuntu

Question

Trying to configure OpenVPN client on my Ubuntu desktop.

Conf file:

remote 192.168.11.103
#192.168.11.103
#85.249.45.106
#dev-node tap0
dev tap
port 5027
ifconfig 10.9.0.74 10.9.0.73
route 192.168.10.0 255.255.255.0 10.9.0.21
route 192.168.11.0 255.255.255.0 10.9.0.21
route 192.168.12.0 255.255.255.0 10.9.0.21
secret /home/k102/Documents/27-73-74_sergeev2.key
verb 4
tun-mtu 1400
mute 10
auth MD5
cipher DES-CBC
comp-lzo

Command:

sudo openvpn --config 27-73-74_sergeev2.ovpn

But I get this error:

Sun Feb 12 12:27:01 2012 us=30542 /sbin/ifconfig tap0 10.9.0.74 netmask 10.9.0.73 mtu 1400 broadcast 255.255.255.254
SIOCSIFNETMASK: Invalid argument
Sun Feb 12 12:27:01 2012 us=36280 Linux ifconfig failed: external program exited with error status: 1
Sun Feb 12 12:27:01 2012 us=36329 Exiting

I can't figure out what I have to do with it. How can I fix this?

Answer 1

From the OpenVPN manual:

--ifconfig l rn

Set TUN/TAP adapter parameters. l is the IP address of the local VPN endpoint. [...] For TAP devices, rn is the subnet mask of the virtual ethernet segment which is being created or connected to.
[...]
For TAP devices, which provide the ability to create virtual ethernet segments, --ifconfig is used to set an IP address and subnet mask just as a physical ethernet adapter would be similarly configured. If you are attempting to connect to a remote ethernet bridge, the IP address and subnet should be set to values which would be valid on the the bridged ethernet segment (note also that DHCP can be used for the same purpose).

You're configuring a TAP device, so the second parameter of your ifconfig directive should be a subnet mask, not an IP address.

ifconfig 10.9.0.74 255.255.255.0 # or whatever mask you need

Answer 2

So where exactly is this configured (server.conf, client.conf, somewhere else) so that when a client connects to the VPN Server, it actually gets a correct subnet mask?