First step

service ipsec stop
service xl2tpd stop
rm -rf /usr/local/sbin/ipsec /usr/local/libexec/ipsec
rm -f /etc/init/ipsec.conf /lib/systemd/system/ipsec.service \
      /etc/init.d/ipsec /usr/lib/systemd/system/ipsec.service

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Second step

Ubuntu/Debian

apt-get purge xl2tpd

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Third step

Ubuntu/Debian

Edit /etc/iptables.rules and remove unneeded rules. 
Your original rules (if any) are backed up as /etc/iptables.rules.old-date-time. 
In addition, edit /etc/iptables/rules.v4 if the file exists.

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Fourth step

Edit /etc/sysctl.conf and remove the lines after # Added by hwdsl2 VPN script.

Edit /etc/rc.local and remove the lines after # Added by hwdsl2 VPN script. 
DO NOT remove exit 0 (if any).

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Optional

Note: This step is optional.

Remove these config files:

/etc/ipsec.conf*
/etc/ipsec.secrets*
/etc/ppp/chap-secrets*
/etc/ppp/options.xl2tpd*
/etc/pam.d/pluto
/etc/sysconfig/pluto
/etc/default/pluto
/etc/ipsec.d (directory)
/etc/xl2tpd (directory)

Copy and paste for fast removal:

rm -f /etc/ipsec.conf* /etc/ipsec.secrets* /etc/ppp/chap-secrets* /etc/ppp/options.xl2tpd* \
      /etc/pam.d/pluto /etc/sysconfig/pluto /etc/default/pluto
rm -rf /etc/ipsec.d /etc/xl2tpd

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