Allowing SSH on a server with an active OpenVPN client

Solution 1:

Based on @MrK answer, I've write some simple code here to make it quicker to do the job so you doesn't have to check for interfaces/IP:

ip rule add from $(ip route get 1 | grep -Po '(?<=src )(\S+)') table 128
ip route add table 128 to $(ip route get 1 | grep -Po '(?<=src )(\S+)')/32 dev $(ip -4 route ls | grep default | grep -Po '(?<=dev )(\S+)')
ip route add table 128 default via $(ip -4 route ls | grep default | grep -Po '(?<=via )(\S+)')

I've tried this script on 4 of my VPS and it's working perfectly.

Solution 2:

This may be a bit late, but ...

The problem is that the default gateway gets changed by OpenVPN, and that breaks your current SSH connection unless you set up appropriate routes before you start OpenVPN.

What follows works for me. It uses iptables and ip (iproute2). Below, it is assumed that the default gateway interface before OpenVPN is started is "eth0". The idea is to ensure that when a connection to eth0 is made, even if eth0 is not the default gateway interface anymore, response packets for the connection go back on eth0 again.

You could use the same number for the connection mark, firewall mark and routing table. I used distinct numbers to make the diffences between them more apparent.

# set "connection" mark of connection from eth0 when first packet of connection arrives
sudo iptables -t mangle -A PREROUTING -i eth0 -m conntrack --ctstate NEW -j CONNMARK --set-mark 1234

# set "firewall" mark for response packets in connection with our connection mark
sudo iptables -t mangle -A OUTPUT -m connmark --mark 1234 -j MARK --set-mark 4321

# our routing table with eth0 as gateway interface
sudo ip route add default dev eth0 table 3412

# route packets with our firewall mark using our routing table
sudo ip rule add fwmark 4321 table 3412

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UPDATE:

The above works fine for me on Debian Jessie. But on an older Wheezy system I have just found that I need to add "via" to the routing table entry:

# our routing table with eth0 as gateway interface
sudo ip route add default dev eth0 via 12.345.67.89 table 3412

There "12.345.67.89" must be the original non-VPN gateway.

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Solution 3:

I'm having a similar issue to this and have been attempting the fix described in this forum post.

The idea is that currently when you connect to your public IP address, the return packets are being routed over the VPN. You need to force these packets to be routed over your public interface.

These route commands will hopefully do the trick:

ip rule add from x.x.x.x table 128

ip route add table 128 to y.y.y.y/y dev ethX

ip route add table 128 default via z.z.z.z

Where x.x.x.x is your public IP, y.y.y.y/y should be the subnet of your public IP address, ethX should be your public Ethernet interface, and z.z.z.z should be the default gateway.

Note that this hasn't worked for me (using Debian and PrivateInternetAccess) but may help you out.