IPv4 & IPv6 CIDR Cheat Sheet(Complete Reference Guide & Real-time Subnet Calculator)
Understanding IPv4 and IPv6 CIDR (Classless Inter-Domain Routing) is essential for network engineers, system administrators, and IT professionals. CIDR simplifies IP address allocation and subnetting by replacing traditional class-based networks with flexible prefix lengths. This guide provides a complete CIDR reference for both IPv4 and IPv6, helping you quickly identify subnet masks, available hosts, network sizes, and address ranges. Whether you're designing enterprise networks, preparing for certifications like CCNA, or troubleshooting IP addressing issues, this cheat sheet serves as a handy reference and practical subnet calculation resource.
IPv4 & IPv6 CIDR Cheat Sheet
Complete Reference Guide & Real-time Subnet Calculator
⚡ Real-time CIDR Subnet Calculator
Invalid IPv4 address format.
Network Address
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Broadcast Address
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First Usable IP
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Last Usable IP
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Subnet Mask
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Wildcard Mask
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Total Addresses
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Usable Hosts
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📐 Subnet Formulas & Calculation Logic
IPv4 Total IPs
Total IPs = 2(32 - Prefix)
/24 → 2^(32-24) = 256 IPs
IPv4 Usable Hosts
Usable = 2(32 - Prefix) - 2
Excludes Network & Broadcast IPs
IPv6 Address Space
Total IPs = 2(128 - Prefix)
/64 → 2^64 = ~18.4 Quintillion IPs
🧩 Address Structure Breakdown
IPv4 Structure (32 Bits / 4 Octets)
1928 Bits (11000000)
1688 Bits (10101000)
18 Bits (00000001)
0 /248 Bits (00000000)
IPv6 Structure (128 Bits / 8 Hextets)
200116 Bits
0db816 Bits
85a316 Bits
000016 Bits
000016 Bits
8a2e16 Bits
037016 Bits
7334 /6416 Bits
IPv6 Address Compression Rules:
1. Omit leading zeros in any hexadecimal 16-bit block (e.g.,
2. Replace consecutive all-zero blocks with
1. Omit leading zeros in any hexadecimal 16-bit block (e.g.,
0db8 → db8).2. Replace consecutive all-zero blocks with
:: (allowed only once per address).
🌐 IPv6 CIDR Reference Table
| Prefix | Total Addresses | /64 Subnets | Common Use Case |
|---|---|---|---|
| /128 | 1 IP Address | 1 / 264 | Single Host / Interface ID / Loopback |
| /127 | 2 IPs | N/A | Point-to-Point Router Links (RFC 6164) |
| /64 | 18.4 Quintillion (264) | 1 Subnet | Standard End-Host Subnet / SLAAC Default |
| /60 | 2.94 × 1019 | 16 Subnets | Small Branch Office / Home Network Delegation |
| /56 | 4.72 × 1021 | 256 Subnets | Standard Customer Assignment (ISP to Home/SME) |
| /48 | 1.21 × 1024 | 65,536 Subnets | Standard Enterprise Site Prefix Allocation |
| /32 | 7.92 × 1028 | 4.29 Billion | Standard ISP Block Allocation (from RIRs) |
| /12 | 1.33 × 1035 | 7.2 × 1018 | Regional Internet Registry (RIR) Allocation |
🔒 Special IPv6 Address Ranges
| Prefix / Range | Type | Description & Scope |
|---|---|---|
| ::/128 | Unspecified Address | Used when no IP is assigned yet (0.0.0.0 equivalent in IPv4) |
| ::1/128 | Loopback Address | Localhost loopback interface (127.0.0.1 equivalent) |
| fc00::/7 | Unique Local (ULA) | Private network addressing (10.0.0.0/8 & 192.168.0.0/16 equivalent) |
| fe80::/10 | Link-Local | Self-assigned for local link communication (non-routable) |
| 2000::/3 | Global Unicast | Publicly routable IPv6 Internet addresses |
| ff00::/8 | Multicast | One-to-many communication (replaces IPv4 broadcast) |
🖥️ IPv4 CIDR Reference Table
| Prefix | Subnet Mask | Total Addresses | Usable Hosts | Class / Typical Use Case |
|---|---|---|---|---|
| /32 | 255.255.255.255 | 1 | 1 | Single Host / Loopback Route |
| /30 | 255.255.255.252 | 4 | 2 | Point-to-Point Router Links |
| /29 | 255.255.255.248 | 8 | 6 | Small Gateway / DMZ Subnet |
| /28 | 255.255.255.240 | 16 | 14 | Small Sub-office / VLAN |
| /27 | 255.255.255.224 | 32 | 30 | Branch Office Subnet |
| /26 | 255.255.255.192 | 64 | 62 | Medium Subnet |
| /25 | 255.255.255.128 | 128 | 126 | Half Class C |
| /24 | 255.255.255.0 | 256 | 254 | Standard LAN / Class C Block |
| /23 | 255.255.254.0 | 512 | 510 | Medium Enterprise LAN (2× Class C) |
| /22 | 255.255.252.0 | 1,024 | 1,022 | Large LAN (4× Class C) |
| /16 | 255.255.0.0 | 65,536 | 65,534 | Standard Class B Block |
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 | Standard Class A Block |
🏢 Private IPv4 Ranges (RFC 1918)
| Class | CIDR Range | Subnet Mask | IP Range |
|---|---|---|---|
| Class A | 10.0.0.0/8 | 255.0.0.0 | 10.0.0.0 – 10.255.255.255 |
| Class B | 172.16.0.0/12 | 255.240.0.0 | 172.16.0.0 – 172.31.255.255 |
| Class C | 192.168.0.0/16 | 255.255.0.0 | 192.168.0.0 – 192.168.255.255 |
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