Mikrotik WAN IP & IP/cloud over PPTP Server WAN

I have PPTP Client on Mikrotik that connected to the internet on WAN ip (125.x.x.x). The PPTP client in the Mikrotik is successfully connected to my PPTP Server on internet CentOS Linux, WAN IP (128.x.x.x) …BUT, the Mikrotik’s WAN ip still return 125.x.x.x. How do I change my Mikrotik’s WAN IP to PPTP Server’s WAN ip address (from 125.x.x.x to 128.x.x.x) so that:

  • my IP/Cloud also DDNS the 128.x.x.x instead of 125.x.x.x, and,
  • when I do the checkmyip.com on the Mikrotik’s LAN network, I also get the 128.x.x.x instead of 125.x.x.x.

Any idea how?

Thanks