How to solve the problem of accessing Synology via VPN?

Question

VPN

Debian server with Softether VPN. Clients on Win7 connect to the server via L2TP using standard means due to NAT with a gray IP. On the other hand, Synology connects via OpenVPN due to a router with a white IP.
Since I did not find a solution with Softether with a static IP address (all of its clients have a virtual mac address) or addressing the client by name, I narrowed the DHCP range so that only one possible pair of addresses [105,106] was available to Synology and to it it was always possible to contact the address 192.168.2.105, which he receives.
Problem: sometimes Softether kicks and disconnects all sessions. At the same time, Synology cannot reconnect and get its 192.168.2.105 back - apparently, some kind of timeout for dnsmasq on the server, although I set the lease to expire after 5 minutes. It cannot receive any other address (see restrictions above) and after a few minutes it gives up reconnect attempts, remaining inaccessible.
How to solve this situation?
I don't want Synology to stick out on its own, so I don't make it a server or release its panel through a router. But in the situation described above, I am left without the ability to connect it back without physical contact.

Answer 1

The only thing that comes to mind is to make the lease time for dnsmasq less than the time after which Synology gives up attempts. But is it good to rent an address every minute?