GCE + OpenVPN + subnetwork does not work the routing - networking

Question

I want to create a Private network in google compute platform where I will be able to enter only using a vpn.
So, I create a machine in GCE and I install openvpn. This machine has an static IP, the ssh port open and the default network configuration from GCE.
Then, I create a second machine (call it MachineA) , in the same network, but without external IP.
Then I create the route rule in order to redirect traffic from vpn-machine to another internal instances.
I'm able to connect from my machine to the vpn.
I'm able to ping to vpn machine.
I'm able to ping to MachineA.
I'm able to ssh to vpn machine.
I'm able to ssh to MachineA.
but...
When I connect to ssh vpn machine and run gsutil it works, also ping to 8.8.8.8
When I connect to ssh MachineA and run gstult or ping 8.8.8.8 does not work.
Any Idea what Im doing wrong ?
Some information
from VPN-machine
xxx#dev-vpn:~$ netstat -rn
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
0.0.0.0 10.240.10.1 0.0.0.0 UG 0 0 0 eth0
10.16.0.0 10.16.0.2 255.255.255.0 UG 0 0 0 tun0
10.16.0.2 0.0.0.0 255.255.255.255 UH 0 0 0 tun0
10.240.10.1 0.0.0.0 255.255.255.255 UH 0 0 0 eth0
xxx#dev-vpn:~$ traceroute 10.240.10.3
traceroute to 10.240.10.3 (10.240.10.3), 30 hops max, 60 byte packets
1 * * instance-1.c.project.internal (10.240.10.3) 1.188 ms
from MachineA
traceroute to 10.240.10.2 (10.240.10.2), 30 hops max, 60 byte packets
1 * * *
2 * * dev-vpn.c.project.internal (10.240.10.2) 0.899 ms
traceroute to 8.8.8.8 (8.8.8.8), 30 hops max, 60 byte packets
1 * * *
2 * * *
3 * * *
4 * * *
5 * * *
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
0.0.0.0 10.240.10.1 0.0.0.0 UG 0 0 0 eth0
10.240.10.1 0.0.0.0 255.255.255.255 UH 0 0 0 eth0
In google networking I add this rule
vpn-routing 10.16.0.0/24 1001 None dev-vpn (Zone us-central1-a)

Answer 1

I have a working system that does this. The innovation I made was to add an alias IP range and make the OpenVPN server use that Google IP range.
So for a router instance, that has an external IP address and will run the OpenVPN server on GCE, you need to create the instance with just one interface and a small IP Alias range. This would then permit IP forwarding from the main interface to the small Alias range. Let's say you are on default network 10.156.0.10/20 and you have added an Alias range of 10.156.1.0/28, you then add as the server line in your OpenVPN server configuration: server 10.156.1.1.
So the tun0 interface of OpenVPN (server-side) will come up on 10.156.1.1 and the tunnel endpoint on 10.156.1.2.
You have to push the routes to the OpenVPN clients (so push 10.156.0.0/20 in the server configuration). You will also need iroute statements in the server's ccd/client.
Here's an excerpt from the OpenVPN server's configuration file:
server 10.156.1.0 255.255.255.240
push "route 10.156.0.0 255.255.240.0"
push "route 10.164.0.0 255.255.240.0"
push "route 10.132.0.0 255.255.240.0"
route 192.168.127.0 255.255.255.0
If your site network is 192.168.127.0/24 and you use 3 Google networks. The ccd/client file has this
route 192.168.127.0 255.255.255.0
iroute 192.168.127.0 255.255.255.0
And you may need to add others, if you have other routes. (There's a section in the OpenVPN manuals about ccd/ and iroute.)
Back on the Google cloud, you will need to add a Google route via the OpenVPN gateway on 10.156.0.10 to get back to 192.168.127.0/24.
And there's lots of firewalling that you should do to make your hosts safe, but you must at least open the 1194 port for OpenVPN.
On your site, if you want to access the Google Cloud private networks, you will need to use RIPd from Quagga. That's a relatively easy configuration:
router rip
network eth0
passive-interface tun0
no default-information originate
redistribute kernel route-map GMAP
access-list GCE permit 10.156.0.0/20
access-list GCE permit 10.164.0.0/20
access-list GCE permit 10.132.0.0/20
access-list GCE deny any
route-map GMAP permit 10
match ip address GCE
This is the RIPd configuration for the OpenVPN client gateway, which is a router. This configuration propagates any routes for the three Google Cloud networks 10.{156,164,132}.0.0/20.
The RIPd configuration on the other hosts in your site network doesn't require any special configuration, just name the "router rip" and the "network eth0", your host's network interface and start RIPd. (The configuration on the VPN client gateway should be easier than this, but I found that "no default-information originate" didn't work for me, so I had to just propagate the Google routes.)