How to force all packets go through ssh tunnel?

You can create VPN using ssh. Here is the relevant section from man ssh:

SSH-BASED VIRTUAL PRIVATE NETWORKS
    ssh contains support for Virtual Private Network (VPN) tunnelling using the tun(4) 
    network pseudo-device, allowing two networks to be joined securely.  The sshd_config(5)
    configuration option PermitTunnel controls whether the server supports this,
    and at what level (layer 2 or 3 traffic).

    The following example would connect client network 10.0.50.0/24 with remote network
    10.0.99.0/24 using a point-to-point connection from 10.1.1.1 to 10.1.1.2,
    provided that the SSH server running on the gateway to the remote network,
    at 192.168.1.15, allows it.

    On the client:

           # ssh -f -w 0:1 192.168.1.15 true
           # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
           # route add 10.0.99.0/24 10.1.1.2

    On the server:

           # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
           # route add 10.0.50.0/24 10.1.1.1

At the end, you will have tunnel interface which you can use to forward your traffic.