- CIDR cheat sheet — subnet masks, private ranges & wildcards
- Quick reference for IPv4 prefixes: RFC 1918 private ranges, special-purpose blocks (loopback, APIPA, multicast), and every subnet from /0 to /32 with mask, usable hosts, and wildcard.
- What is CIDR?
- Classless Inter-Domain Routing writes an IPv4 address and its network prefix together, like 10.0.0.0/24. The number after the slash is how many leading bits belong to the network.
- What does the prefix length mean?
- A /24 means the first 24 bits identify the network and the remaining 8 bits identify hosts (256 addresses). Smaller prefixes cover larger ranges; larger prefixes cover fewer hosts.
- What are network and broadcast addresses?
- The network address is the first address in the block (all host bits zero). The broadcast address is the last (all host bits one). On prefixes shorter than /31 they are usually reserved and not assigned to hosts.
- What about /31 and /32?
- A /32 is a single host. A /31 is a point-to-point link (RFC 3021) where both addresses are usable.
- How does subnet splitting work?
- Equal splits borrow host bits to create more network bits. Splitting into 2, 4, 8, or 16 subnets adds 1–4 bits to the prefix (e.g. /24 → four /26s).
- What do the IPv4→IPv6 forms mean?
- IPv4-mapped (::ffff:…) embeds an IPv4 address in IPv6 for dual-stack APIs. 6to4 (2002:…) builds a /48 from the IPv4. NAT64 (64:ff9b::…) is the well-known translation prefix.