Switch

Two hosts plugged into the same switch do not automatically belong to the same local network. In the field, a problem may look like “the IP is wrong” or “the firewall is blocking it”, but it may have died earlier at the Layer-2 boundary: ARP broadcasts only spread on part of the ports, DHCP Discover never leaves the segment, and packet capture shows traffic on the link while the target device still acts as if it were on another network.