if not using DDNS, how can dail up be configured to set up site to site VPN?

Hello @danielchoy ,

If you enable nat-t on both sites, you can establish ipsec vpn between both sites.

https://community.fortinet.com/t5/FortiGate/Technical-Tip-IPSec-VPN-nattraversal/ta-p/197873

But, suddenly ip address can be changed on the ppoe site. Because of that every time you need to change the remote IP configuration on the static side. This is an uncomfortable configuration.

If you don't want to use ddns on the ppoe site, you can use a dial-up vpn. In this scenario, you need to configure a static site as a dial-up server. The ppoe site can connect to this server even if the IP address changes.

You can review this document about dial-up vpn.

https://docs.fortinet.com/document/fortigate/6.2.16/cookbook/6896/fortigate-as-dialup-client

Hi @danielchoy 

From the statement, here is my understanding:

SiteA - Fixed IP

SiteB - DHCP or PPPOE

Based on this scenario, you can do dial-up VPN.
SiteA will be the Hub(server) , SiteB will be the spoke(client).

This KB will be helpful:
https://community.fortinet.com/t5/FortiGate/Technical-Tip-Dialup-VPN-Configuration-Between-Two-FortiGates/ta-p/197667

https://docs.fortinet.com/document/fortigate/7.4.4/administration-guide/853412/ipsec-vpn-wizard-hub-and-spoke-advpn-support

Hope that helps.