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Will a broadcast on a supernet broadcast address reach all the subnets?

For example if I sent a broadcast to the address 10.172.255.255, would it affect the clients in the subnet 10.172.2.0/24?

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No, directed broadcast only works on the layer-2 segment that it ends up at. A packet to 10.172.255.255 would end up as a broadcast to for example 10.172.255.0/24 or 10.172.255.128/25 or 10.172.254.0/23 or ... etc ... depending on which subnet ends at that address.

And that is assuming that a subnet ends there! If the subnet is 10.172.0.0/15 then 10.172.255.255 is just a normal address in the middle of the subnet.

Because causing broadcasts in a remote network is a great way to do a denial of service attack most networks have disabled directed broadcasts. IPv6 doesn't even have them anymore.

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