Understanding IPv4 and CIDR prefixes
A practical introduction to IPv4 addresses, subnetting and CIDR aggregation, with IETF RFC references.
What is IPv4 for?
IPv4 carries datagrams between networks using 32-bit addresses, commonly written as four decimal numbers separated by dots, for example 192.0.2.10. An address alone does not always identify the host’s network: the prefix states how many leading bits identify the network portion.
RFC 791 is the original foundational specification of the IPv4 Internet Protocol. It dates from 1981; today’s networks also rely on later RFCs for many behaviors and operational practices.
Subnets and CIDR
A notation such as 192.0.2.0/24 means that the first 24 bits form the network prefix. The remaining bits determine the addresses in the block. CIDR supports variable-length prefixes instead of the older fixed class-based allocation model.
Route aggregation summarizes contiguous prefixes into a shorter prefix when their alignment allows it. An overly broad summary can include unwanted addresses, so SumHexa’s aggregator never expands the set of addresses provided.
Calculator limitations
These tools return mathematical results based on the values entered. They do not check whether a range is allocated, routing policies, local reservations or your network provider’s rules. Documentation ranges such as 192.0.2.0/24 are for examples and documentation, not ordinary public use.
Related calculators
Official references
- RFC 791 — Internet Protocol
Original foundational IPv4 specification (1981).
- RFC 4632 — Classless Inter-domain Routing (CIDR)
IETF best current practice for CIDR address assignment and aggregation.