My ISP just changed out my old Arris Surfboard cable modem/router for a new (purportedly faster) Arris DG3270 “Gateway” combo cable modem/router/wi-fi, but I think the change might have created a security issue.
In my previous home network configuration I had 3 Windows 10 computers wired directly to 3 of the LAN ports on the back of the Surfboard. The 4th LAN port was connected to the WAN port on a D-Link DIR-655 router which provided a good wi-fi signal throughout the house for iPhone and iPad, and all worked perfectly. The ISP technician said he could provide a similar setup with the new Arris Gateway device by switching off its wi-fi. He connected LAN port 1 on the back of the Arris Gateway to LAN port 1 on the back of the D-Link router and not to the WAN port (which I understand effectively converted the D-Link into a switched wi-fi device and avoided potential double NAT and DHCP problems), and LAN ports 2, 3, and 4 on the back of the Arris Gateway to the 3 Windows 10 computers.
The Arris Gateway user GUI for the new device shows Routing, Wireless 2.4GHz and 5GHz settings NOT enabled, DHCP and DHCP server settings enabled, and NAT mode selected is Bridged. All settings on the Firewall page are enabled.
The ISP’s Public IP address currently assigned to me is 24.x.x.x. However, when I run ipconfig /all from the Windows 10 command line I see that the private IPv4 address for the computer I am currently using, and the Default Gateway also show as 24.x.x.x addresses. The range of available private IP addresses shown in the Arris GUI DHCP area is 192.168.0.2 to 192.168.0.254 and I expected to see private IP and Default Gateway addresses in this range. I am therefore wondering whether the ISP technician somehow disabled the Arris Gateway DHCP server and effectively connected my home network directly to the internet with no separation between public/private segments, and if so whether incoming traffic is even passing through the Arris Gateway Firewall to filter out undesirable and/or malicious material.
Any information or comments that help me understand what is going on would be greatly appreciated.
Edited by mjyeo, 13 February 2018 - 10:08 PM.