Subnet

subnetwork or subnet is a logical subdivision of an IP network. This results in the logical division of an IP address into two fields, the routing prefix and the host identifier


Host identifier
The host identifier is an identifier for a specific host or network interface.

Routing prefix
CIDR
The routing prefix may be expressed in Classless Inter-Domain Routing (CIDR) notation written as the first address of a network, followed by a slash character (/), and ending with the bit-length of the prefix.

NETMASK
For IPv4, a network may also be characterized by its subnet mask or netmask, which is the bitmask that when applied by a bitwise AND operation to any IP address in the network, yields the routing prefix.

Traffic is exchanged between subnetworks through routers when the routing prefixes of the source address and the destination address differ. A router serves as a logical or physical boundary between the subnets.

Problem

Our goal is to be able to ping target devices with different subnet but in the same physical network. But the traffic from my PC will send the ICMP packet to the gateway and then it’s gone. So we need to redirect the ICMP packet to the target devices.

The solution is to set a routing rule for a device with netmask 255.255.255.255 (host routing). So that the PC will send ARP and ICMP packets directly to the switch and then to the target devices.

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