So my home internet router outside interface have an IP 158.x.x.137 and 158.x.x.129 as default gateway which is /25 network, and the inside interface have an IP 192.168.1.1 which is the default gateway itself (my home LAN /24).
If my understanding is correct then the entire 158.x.x.128/25 is all of the customer of my ISP right? I can ping all of them under 2ms (basically my neighbor). So all of us is under the same switch connected to the inside interface of my ISP router (158.x.x.129) right?
Then what the outside interface of my ISP router connected to? I meant the inside interface have already a public route able IP address. Is it the same address on both end? And also obviously they have more than 128 customer, how they connect that?
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That router is likely not an outside router. More likely it’s an inside router for your neighborhood or a group of neighborhoods.
Your ISP would have more than 128 IP addresses, so you wouldn’t get outside of your ISP’s network until you hit a bigger router or group of routers that handle the ISP’s connection to probably several other ISP’s so they all together form a backbone.
You can sometimes see this if you do a tracert on a system to something public like google.com. You usually will find that your first several hops are for your ISP.
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