Subnetting a /24

Which Subnet Is This Host

A host is in the subnet produced by applying the mask to the host address. The mask table makes membership visible as a recomputed network row.

highlighted = computed this step

Why membership is arithmetic

A host belongs to the subnet produced by address AND mask. The mask table exposes that membership as the network row.

/26/26

Find this host's subnet

192.168.1.130 with /26 produces network 192.168.1.128. That is the row from the split table.

0xc0a80182&0xffffffc0=0xc0a801800xc0a80182\mathbin{\&}0xffffffc0=0xc0a80180
Host membershipThe host's subnet is the recomputed network row.Host to subnet/26 mask 255.255.255.192address11000000101010000000000110000010192.168.1.130 0xc0a80182mask11111111111111111111111111000000255.255.255.192 0xffffffc0network11000000101010000000000110000000192.168.1.128 0xc0a80180

Decode it again

192.168.1.200 with the same /26 mask produces 192.168.1.192. The last octet moves from 200 to 192.

200&192=192200\mathbin{\&}192=192
Host membership againA different host lands in a different recomputed subnet.Another host/26 mask 255.255.255.192address11000000101010000000000111001000192.168.1.200 0xc0a801c8mask11111111111111111111111111000000255.255.255.192 0xffffffc0network11000000101010000000000111000000192.168.1.192 0xc0a801c0

Summary

Subnet membership is not a verbal category; it is the network result of address AND mask. Address arithmetic only; timing/throughput is not modeled here.

network=0xc0a80180\text{network}=0xc0a80180
Host membershipThe host's subnet is the recomputed network row.Host to subnet/26 mask 255.255.255.192address11000000101010000000000110000010192.168.1.130 0xc0a80182mask11111111111111111111111111000000255.255.255.192 0xffffffc0network11000000101010000000000110000000192.168.1.128 0xc0a80180