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Let it be this diagram:

enter image description here

Can I assign such networks at each segment without overlapping? In my understanding each network has a range of usable IPs and those ranges overlapps each other.

For instance, the 10.0.0.0/24 overlapps the 10.0.0.0/29, that overlapps the 10.0.0.0/30. There are some IPs that are common to each network. So hypothetically can be some hosts with the same IP address, in different network segments.

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Can I assign such networks at each segment without overlapping?

Yes, you must. But you have done the exact opposite.

In my understanding each network has a range of usable IPs and those ranges overlapps each other.

IP subnets cannot overlap. Every host must have a unique IP address, just like every phone has a unique telephone number.

Suppose your router has to forward a packet with the address 10.0.0.2. Which interface will your router use? That address could be on any of the interfaces.

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First, you have three interfaces on the same router with the same IP. That's not generally possible. (ignoring VRFs)

From a routing perspective, yes, subnets always overlap. That's how hierarchical routing works. But from a practical (assigned to interfaces) perspective, one should never overlap networks. It is, however, possible to do; as this is the realm of proxy-arp, no one should ever want to. (most modern commercial routers [cisco, juniper, etc] cannot be setup like this anymore.)

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  • I don't know about vendors of hardware routers, but Linux is quite happy to assign the same IP address to multiple interfaces. Mar 5 at 6:32
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    Linux (BSD, and windows) aren't "routers", but they play one on TV. While it can be done, it leads to all manner of confusion for those who try it. (which interface is going to be used? just because traffic came in on one interface doesn't mean an apps reply will go back out that same interface.) Router software running on Linux often will not allow such erroneous configuration. (just like a lot of switch ASICs will allow multiple untagged vlans on a port, but no software allows it)
    – Ricky
    Mar 5 at 9:21

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