Update the public IP address to reflect the new location or configuration.
Update the public IP address to reflect the new location or configuration.
When your device connects online, renewal maintains the same IP address—similar to a standard network setup. Losing your IP is uncommon after a lease renewal, but rebooting your modem precisely at the right moment might cause it to drop. This risk depends on the lease duration and can differ based on location and provider.
Since the ISP runs its own DHCP server, that’s exactly what I’m demonstrating. My modem lacks a built-in router, so I don’t rely on a standard gateway. With configurations like mine, you can use MAC address cloning on the router to change the device’s identity. After rebooting the modem, it sees a fresh MAC address and requests a new IP. Because the previous one was tied to that MAC, the system updates accordingly.
In short, you don’t need to contact the ISP directly. Over ten years with Comcast, their staff have unique expertise—most people don’t even understand what an IP address is.
The IP address remains stable because of its TTL or immediate expiration settings. Updating the MAC address on the router doesn’t affect the IP assigned by your ISP. You’re still asking about DHCP details, which is why it matters.
Updating the WAN port's MAC address allows you to switch the dynamic IP assigned by most ISPs, as the previous IP becomes tied to the old MAC address.
When the IP was tied to a specific MAC address, the ISP would have many unused IPs available. Changing the MAC address simply forced the TTL to reset. The MAC address doesn’t influence how the ISP allocates IP addresses, whether statically or automatically.
This process isn't automatic. Reservations will expire if not updated after their refresh interval. The MAC address links the reservation to the ISP's network, connecting the modem/router or standalone modem to the router. This directly relates to how an ISP assigns IP addresses.
They didn't make sense of what was happening. If the ISP tied the IP to every MAC address, it would create major internal issues. The MAC address is assigned to each network segment; when you alter it, the ISP assumes you're a different device and gives you a new IP. In short, you're overriding the TTL or DHCP timer as they were called.
This explains how MAC addresses function at the local level. A MAC address operates on the second layer and stays within the immediate connection. That’s why it’s referred to as link local. Only one MAC address is visible to the ISP’s servers for scheduling—typically the router’s MAC or the system’s MAC in a combo device. Another key MAC is the HFC MAC of the modem, which enables it to join the network, especially with a DOCSIS provider.
Before discussing who doesn't understand how things function, verify your own information. Each device has a unique MAC address—this is essential for internet communication. Without it, using Ethernet or any link isn't possible. If your ISP links each IP to every MAC on a device, the IP stays tied to something that doesn’t exist, causing internal issues. The MAC serves as a distinct identifier for the network interface card. Changing the MAC forces the DHCP server to treat it as a new device, assigning a fresh IP. Essentially, the "Timer" you see on the DHCP server (TTL or Time To Live) will end when you switch the MAC, prompting a new assignment. I recommend exploring IPv4, MAC addresses, and DHCP further. Stop misunderstanding—this is confusing.