I noticed this today while labbing at work, and now have replicated it at home. I'm certain I'm missing something obvious, but for the life of me can't figure out what it is. When I ping 10.1.x.x I always get a response, despite there not being any such hosts on the network.
My lab at work (standalone) is on a 10.10.18.0/23 network. No routes to any other networks. Pinging 10.1.x.x or 10.2.x.x gets responses from those addresses.
I thought it must be something with my subnetting, but investing at home led me to the same results - on a 192.168.0/24 network. A traceroute takes me through my gateway then a couple of 100.127.x.x hosts, so now I'm wondering if it has to do something with NAT and my ISP (same provider at both locations).
Even though I'm just starting my work towards CCNA, I'm feeling dense for not being able to figure this out. It's not causing any problems, which leads me to believe even more it must be some fundamental and expected thing I am overlooking. Can someone please point me in the right direction?