192.168.100.0/24 — the cable modem's front porch
192.168.100.1 is one of the most useful addresses in home networking: the status page of nearly every DOCSIS cable modem ever shipped — Arris, Motorola, Netgear, Hitron and their ISP-branded twins. The modem hosts it on its own little 192.168.100.0/24 network, separate from whatever LAN you run.
Crucially, it answers even in bridge mode. The modem passes your traffic straight through to the ISP while still serving diagnostics on the side — exactly what you want when the Internet is down and you need to know why.
| Network address | 192.168.100.0 |
| Subnet mask | 255.255.255.0 |
| Wildcard mask | 0.0.0.255 |
| Broadcast address | 192.168.100.255 |
| First usable | 192.168.100.1 |
| Last usable | 192.168.100.254 |
| Total addresses | 256 |
| Usable hosts | 254 |
Why it's reachable through your router
The page lives on the modem's side of the link, so your router needs a route to it. Most consumer firmware handles this automatically by giving the WAN interface a secondary 192.168.100.x address; if 192.168.100.1 does not load, that missing route is why — add a static route or a secondary WAN IP and the page appears.
What you find there is gold for troubleshooting: downstream and upstream power levels in dBmV, SNR per channel, and an event log full of T3/T4 timeouts. ISPs will ask for these numbers — now you can read them yourself.
The mild security footnote
The status page traditionally ships with no login at all — it is read-only diagnostics, so vendors skip authentication. That means anyone on your LAN can read your signal levels and, on some models, reboot the modem with a crafted request. Not a catastrophe, but a decent argument for guest-network isolation.
CIDR Calculator
Run the math on 192.168.100.0/24 — or any other block
Frequently asked questions
What is 192.168.100.1?
The built-in status page of most DOCSIS cable modems: signal levels, channel bonding, event logs and uptime. It works even when the modem is in bridge mode and your own router handles the LAN.
Why can't I open 192.168.100.1?
Your router probably lacks a route to the modem's subnet. Many routers add it automatically; otherwise give the WAN interface a secondary address in 192.168.100.x or a static route for 192.168.100.0/24.
What are good downstream power levels on a cable modem?
Roughly −10 to +10 dBmV downstream with SNR above about 33 dB, and upstream power below about 50 dBmV. Values outside that window point at wiring, splitter or plant problems.