Technical Tip: PPTP VPN disconnecting inside IPSEC dialup tunnel

In some scenarios, PPTP VPN needs to be connected as well while keeping using IPSEC dialup VPN to access remote resources. 

IPSEC VPN can be configured by using the below KB article: Technical Tip: How to configure IPsec remote access with full tunnelling

For a PPTP VPN stable connection, use the below settings:

MTU override enable on IPSEC tunnel:

config system interface
    edit <VPN_Tunnel_Name>
        set mtu-override enable
    next
end

Lower the policy MTU on the policy passing PPTP traffic:

config firewall policy
    edit <policy vpn > lan>
        set tcp-mss-sender 1300
        set tcp-mss-receiver 1300
    next
end

If PPTP VPN is still disconnecting, disable honor-df using the commands below:

config system global
   set honor-df disable
end