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Strange Ethernet Direct Connection Between Mac and Windows Despite Different Subnets (alien.top)

submitted 11 months ago by [email protected] to c/[email protected]

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Hello everyone!

I've had a strange networking problem that I cant explain. Here's the situation:

I have a Mac and a Windows PC connected directly to each other using an Ethernet cable.

The Mac is manually set with the IP 10.0.1.1and a subnet mask of 255.255.255.0.

The Windows machine is set to 10.0.0.1with the same subnet mask.

By all standard networking rules, they shouldn't communicate since they're configured to be on different subnets. Yet, they are still able to send data to each other.

To add to the context, both machines are also connected to the internet via Wi-Fi through my home router. But for the file transfer over Ethernet, they're just directly connected—no routers or switches involved.

Here's what I've already considered and checked:

No additional routes are set up that would explain the cross-subnet communication.
No link-local addresses (APIPA) are being used for the Ethernet interfaces.
The Wi-Fi network is on a completely different IP range.

Any Idea what may me be causing this ?

Thanks in advance for your help!

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[–] [email protected] 1 points 11 months ago

If you are addressing the devices directly by IP, then the destination addresses are correct in the packet headers. The devices will respond with packets addressed to the source IP in the packets they receive.

https://serverfault.com/questions/157970/gateway-understanding-packet-details-ip-and-mac-addresses

The reason this is working is because the devices are still attempting to communicate in a best effort scenario.

This may work using a network switch, depending on how much processing is happening.

The more devices in the routing path, the less likely the packets are to tech their intended destination.

The point of this networking is to create reliable communication between groups of networks. The further off script one goes, the less predictable the communication becomes.