We've been replacing many Ubiquiti EdgeRouters in our client environments to UDM Pros. One quirk of the EdgeRouter is you were able to L2TP into a LAN subnet. UniFi never let this occur, now or in the past. You were forced to create a separate network and route the the LAN via sending all traffic over VPN, or adding routes.
Most of our system installs have a Windows server running SSTP for the Windows-based clients. Some require L2TP for Mac or Linux clients. Here's how to selectively route to your LAN on macOS while NOT sending all traffic. Note: The file below will run on any VPN connection so it may not be a good solution for multiple VPNs on the same Mac. Typically our clients' users only use the a single VPN and nothing else.
Create the file /etc/ppp/ip-up with following content:
/sbin/route add <SUBNET> -interface $1
<SUBNET> with subnet, you want to route through VPN (for ex. 192.168.0.0/16)
execute as root:
chmod 0755 /etc/ppp/ip-up
This file will be executed each time you connect to VPN.
The parameters given to the script:
$1: The VPN interface (e.g.
$2: Unknown, was
0 in my case
$3: IP of the VPN server
$4: VPN gateway address
$5: Regular (non-vpn) gateway for your lan connections
Credit to this Superuser post from 12 years ago!