Cisco Subnet – Why Can Ping These Subnets from a Different Subnet?

arpciscopacket-tracersubnetswitching

I wonder why I can ping 192.168.3.50 /27 and 192.168.3.70 /27 from 192.168.3.100 /24. Is is not supposed to be impossible?

Problem to understand subnets

Thanks in advance for your help.

Best Answer

The host with the /24 address thinks that all the other hosts are on the same network, so it will happily send out a ping on the layer-2 network.

For a response to be sent back, the hosts need to believe that the requesting host is on the same network, otherwise the hosts will try to send a response to their configured gateways. There is something wrong in the configuration of the two hosts which do respond. Unfortunately, host configurations are off-topic here. The masks may be incorrectly configured, or, as I have seen in a few hosts, they do not have a gateway configured so they do respond. You need to figure out what is wrong with the configurations on those two hosts.

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