$ifconfig
tun0      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
          inet addr:10.0.0.1  P-t-P:10.0.0.1  Mask:255.255.255.255
          inet6 addr: fe80::ce51:67bd:73e8:fe63/64 Scope:Link
          UP POINTOPOINT RUNNING  MTU:1500  Metric:1
          RX packets:1665 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1665 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500
          RX bytes:261471 (261.4 KB)  TX bytes:261471 (261.4 KB)

$cat /etc/sysctl.conf
#
# /etc/sysctl.conf - Configuration file for setting system variables
# See /etc/sysctl.d/ for additional system variables.
# See sysctl.conf (5) for information.
#

#kernel.domainname = example.com

# Uncomment the following to stop low-level messages on console
#kernel.printk = 3 4 1 3

##############################################################3
# Functions previously found in netbase
#

# Uncomment the next two lines to enable Spoof protection (reverse-path filter)
# Turn on Source Address Verification in all interfaces to
# prevent some spoofing attacks
net.ipv4.conf.default.rp_filter=0
net.ipv4.conf.all.rp_filter=0

# Uncomment the next line to enable TCP/IP SYN cookies
# See http://lwn.net/Articles/277146/
# Note: This may impact IPv6 TCP sessions too
#net.ipv4.tcp_syncookies=1

# Uncomment the next line to enable packet forwarding for IPv4
net.ipv4.ip_forward=1

# Uncomment the next line to enable packet forwarding for IPv6
#  Enabling this option disables Stateless Address Autoconfiguration
#  based on Router Advertisements for this host
#net.ipv6.conf.all.forwarding=1


###################################################################
# Additional settings - these settings can improve the network
# security of the host and prevent against some network attacks
# including spoofing attacks and man in the middle attacks through
# redirection. Some network environments, however, require that these
# settings are disabled so review and enable them as needed.
#
# Do not accept ICMP redirects (prevent MITM attacks)
#net.ipv4.conf.all.accept_redirects = 0
#net.ipv6.conf.all.accept_redirects = 0
# _or_
# Accept ICMP redirects only for gateways listed in our default
# gateway list (enabled by default)
# net.ipv4.conf.all.secure_redirects = 1
#
# Do not send ICMP redirects (we are not a router)
#net.ipv4.conf.all.send_redirects = 0
#
# Do not accept IP source route packets (we are not a router)
#net.ipv4.conf.all.accept_source_route = 0
#net.ipv6.conf.all.accept_source_route = 0
#
# Log Martian Packets
#net.ipv4.conf.all.log_martians = 1
#
$ sudo sysctl -w net.ipv4.conf.tun0.rp_filter=0
$ sudo sysctl -w net.ipv4.conf.all.rp_filter=0
$ sudo sysctl -w net.ipv4.ip_forward=1
$ sudo ip route add default dev tun0 table John
$ ip rule
0:      from all lookup local
32766:  from all lookup main
32767:  from all lookup default
$ sudo ip rule add fwmark 0x1 table John
$ sudo iptables -t mangle -I OUTPUT -o wlp2s0 -j MARK --set-mark 1
$ ping -c 1 8.8.8.8
fails