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What would happen if 2 routers on the same ISP or same ISP WAN IP subnet had the same MAC? (alien.top)

submitted 9 months ago by [email protected] to c/[email protected]

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Just a random question/thought that popped up in my head: If you had one router with its real mac address connected to the internet on a particular ISP, and you cloned the Mac of another router to make it the same of the 1st one and connected it to the same ISP, would it make the connections for both or just one connection unstable, not work at all or would the ISP-level routing work around it?

As far as I'm aware ISPs (at least Virgin) lease routers their IP address based on their MAC. Essentially the ISP will be trying to lease the same IP to 2 devices at once.

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[–] [email protected] 1 points 9 months ago

It depends on how the last mile access is configured.

Sometimes layer 2 end segments are shared (like doccis) it would break those 2 devices on doccis.

I don't believe the gpon standard has the same problem.

It would cause a problem on wireless based access or on embedded ISPs in buildings, they usually shortcut and just put a /24 and push users are onto the same vlan.

Again it only breaks those 2 devices, unless the network sees mac-moves and blocks a port.