Some ISP's like Charter have their systems configured in such a way that from a customers router the ARP table for all of the IP's in the subnet show the same MAC address. The IP it hands off through their modem to the CPE router is a /22. When you traceroute from the customer router it has one hop between IP's within the same /22 subnet. Now the same test on Wave broadband shows the real MAC addresses of all routers in the subnet and traceroutes are direct to other IP's within the subnet. I am interested to know how they accomplish the first example. Would this be a form of PVLAN?
