How to configure L2TP over IPSec on a FortiGate

Description
The following CLI syntax can be used to configure an L2TP over IPSec tunnel and was tested to work for a connection between a Windows 8.x Tablet and a FortiGate.

Solution
Text which is presented in '< >' needs to be updated to match your environment.

Syntax:

config system global
    sset gui-policy-based-ipsec enable
end

config user local
    edit "<select_username>"
        set type password
        set passwd <create_password>
    next
end

config user group
    edit "L2TP"
        set member "<select_username>"
    next
end

config vpn l2tp
    set sip <first ip in range>
    set eip <last ip in range>
    set status enable
    set usrgrp "L2TP"
end

config vpn ipsec phase1
    edit "L2TP_WINRT_P1"
        set type dynamic
        set interface "wan1"
        set keylife 28800
        set proposal aes256-md5 3des-sha1 aes192-sha1
        set add-route enable
        set dhgrp 2
        set psksecret <enter_preshared_key>
    next
end

config vpn ipsec phase2
    edit "L2TP_WINRT_P2"
        set phase1name "L2TP_WINRT_P1"
        set proposal aes256-md5 3des-sha1 aes192-sha1
        set pfs disable
        set encapsulation transport-mode
        set keylifeseconds 3600
    next
end


conf firewall address

edit "L2TP_Clients"
        set type iprange
        set start-ip <first ip in range>
        set end-ip <last ip in range>
    next
end

config firewall policy
    edit 0
        set srcintf "wan1"
        set dstintf "wan1"
        set srcaddr "all"
        set dstaddr "all"
        set action ipsec
        set schedule "always"
        set service "ALL"
        set inbound enable
        set outbound enable
        set vpntunnel "L2TP_WINRT_P1"
    next

    edit 0
        set srcintf "wan1"
        set dstintf "wan1"
        set srcaddr "L2TP_Clients"
        set dstaddr "all"
        set action accept
        set schedule "always"
        set service "ALL"
        set nat enable
    next
    edit 0
        set srcintf "<internal_interface>"
        set dstintf "wan1"
        set srcaddr "all"
        set dstaddr "L2TP_Clients""
        set action accept
        set schedule "always"
        set service "ALL"
        set nat enable
    next
    edit 0
        set srcintf "wan1"
        set dstintf "<internal_interface>"
        set srcaddr "L2TP_Clients"
        set dstaddr "all"
        set action accept
        set schedule "always"
        set service "ALL"
        set nat enable
    next
end

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