Subnet Zero
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Subnet Zero is a computer networking term for the first subnet obtained after subnetting a network address.
Using subnet zero for addressing was discouraged at one point due to the confusion created by having a network and subnet with the same address. According to RFC 950, "It is useful to preserve and extend the interpretation of these special (network and broadcast) addresses in subnetted networks. This means the values of all zeros and all ones in the subnet field should not be assigned to actual (physical) subnets."
This practice of avoiding subnet zero eventually became obsolete with RFC 1878, published in 1995.
