I am using Synology Router RT1900AC

Initially, I purchased it to use L2TP VPN.

One day, the L2TP VPN was shut off because of a problem with Korean ISP companies.

Some were accessible and some were not.

The problem appears to occur in the process of transferring data from each ISP company.

I think it's the case that the data is transferred from the ISP company to another ISP company.

If you want to use VPN in Korea, it would not be a big problem to use OpenVPN for most people.

I'll give you the first tip of the RT1900AC OpenVPN setup task.

If you put the Ovpn file into your smartphone, it will work perfectly fine.

However, when installed on Windows, internal network behavior and external ping will be normal, but the Internet will not be able to function properly.

You can search everywhere for other settings, but there is no description for this tip.

It was a method to force the DNS value to be set.

**Like this. KT(korean Telecom) DNS : 168.126.63.1

dhcp-option DNS: To set primary domain name server address.

Repeat this option to set secondary DNS server addresses.

dhcp-option DNS 168.126.63.1