I have a router TP-Link Archer C7 v5 with latest update set up in router mode.

LAN that it creates:

router's LAN IP: 192.168.1.1, mask 255.255.255.0

given the following, LAN's IP address is 192.168.1.0

There is PPTP server set up on this router.

PPTP server is configured to assign the IP addreses between 10.0.0.50 to 10.0.0.59

The first client's possible IP is 10.0.0.50

Consequently, PPTP server's DNS server is 10.0.0.49

Windows 10 can't connect to the Internet, when connected to the VPN server from this router.

The network configuration that it receives:

PPP adapter My VPN connection:

   Connection-specific DNS Suffix  . :
   IPv4 Address. . . . . . . . . . . : 10.0.0.51
   Subnet Mask . . . . . . . . . . . : 255.255.255.255
   IPv4 Address. . . . . . . . . . . : 192.168.1.50
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.1.1

We can see here, the PPTP from the router has given two IP addresses.

The first would be good:

   IPv4 Address. . . . . . . . . . . : 10.0.0.51
   Subnet Mask . . . . . . . . . . . : 255.255.255.255

PPTP is end-to-point connection, as such the mask 255.255.255.255 is valid here.

Then:

   IPv4 Address. . . . . . . . . . . : 192.168.1.50
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.1.1

This is invalid. Shouldn't have been sent by router.

The following IP was calculated and sent by router to Windows 10: (PPTP server's first possible client IP 10.0.0.50 and LAN subnet 255.255.255.0 or LAN network IP 192.168.1.0) = 192.168.1.50

The incorrect second IP and subnet mask is being to the client.

The problem will be noticeable on Windows 10. On the other side Android will only use the first IP address and subnet mask sent, the VPN connection works.

The firmware needs to be fixed to solve this problem.