I have a site-to-site VPN setup between a UDM Pro and a SonicWall TZ400. The traffic between both local networks is working just fine. I also have an L2TP VPN setup on the UDM Pro for users of this office when they are working from home. Traffic from the VPN to the local network is also just fine.
HOWEVER, my issue is that I need the L2TP clients to be allowed to access resources on the remote site-to-site VPN network. This traffic is not allowed and I cannot figure out why. I have enabled the Site-To-Site VPN checkbox on the L2TP network. That has had no affect. I also attempted to create a firewall rule and created network groups for the L2TP network and site to site network but unless I did not configure that correctly, that also did not work.
SOLUTION \ DONT FORGET TO ADD THE NETWORK SUBNET OF THE L2TP NETWORK TO THE REMOTE IPSEC's ALLOWED SUBNETS. ONCE THATS DONE IT WILL WORK