When I ran into some intermittent Internet connectivity issues the other day at home, I decided to do something I rarely bother with - I plugged my laptop directly into the cable modem to see what was up. Once the connection came back up, I decided to do some diagnostics while I was still directly connected to be sure everything was properly functioning.
During this test:
- My laptop was plugged directly into the cable modem.
- As far as I know, this is a "dummy" modem - it's not an all-in-one cable modem/router/wifi device.
- I had no other devices on the network being tested.
- My laptop received an IP address and gateway via DHCP, both of which were publicly-routable "Class A" addresses.
If I ran a
tracert to the gateway, everything came back normal - nothing appeared to be in between my laptop and the gateway.
However, when I ran the same utilities against other targets (Google, Yahoo, etc.) on the Internet, the first hop came back in the "Class A" range of RFC 1918 addresses. Also, the publicly-routable Default Gateway address did not show up at all in the traces.
Again, the only devices connected in my house at this point were my laptop and the cable modem. So, presumably the first hop to any address not in my DHCP-assigned subnet should always be whichever address shows up in
ipconfig as the "Default Gateway".
Could someone explain how this can happen, and why there might be legitimate reason for it?