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IPv6 CIDR Notation Reference
Complete reference table for IPv6 CIDR prefixes with address ranges and subnet calculations. Essential guide for IPv6 network design.
Common IPv6 Address Types
2000::/3 Global Unicast
2001:db8::/32 Documentation
fc00::/7 Unique Local (ULA)
fe80::/10 Link-Local
ff00::/8 Multicast
::1/128 Loopback
Standard Allocations
/29 - RIPE ISP allocation(8× more generous than /32! 🎁)
/32 - Standard ISP allocation (ARIN, APNIC, etc.)
/48 - Site/Organization (recommended)
/56 - Residential/Small business
/64 - Single subnet (standard size)
/128 - Single host address
CIDR Reference Table
| Prefix | Total Addresses | Total /64 Subnets |
|---|---|---|
| /0 | ≈3.40e+20 (340282366920938487808.0 quintillion) | ≈1.84e+1 (18.4 quintillion) |
| /1 | ≈1.70e+20 (170141183460469243904.0 quintillion) | ≈9.22e+0 (9.2 quintillion) |
| /2 | ≈8.51e+19 (85070591730234621952.0 quintillion) | ≈4.61e+0 (4.6 quintillion) |
| /3 | ≈4.25e+19 (42535295865117310976.0 quintillion) | ≈2.31e+0 (2.3 quintillion) |
| /4 | ≈2.13e+19 (21267647932558655488.0 quintillion) | ≈1.15e+0 (1.2 quintillion) |
| /5 | ≈1.06e+19 (10633823966279327744.0 quintillion) | ≈5.76e+2 (576.5 quadrillion) |
| /6 | ≈5.32e+18 (5316911983139663872.0 quintillion) | ≈2.88e+2 (288.2 quadrillion) |
| /7 | ≈2.66e+18 (2658455991569831936.0 quintillion) | ≈1.44e+2 (144.1 quadrillion) |
| /8 | ≈1.33e+18 (1329227995784915968.0 quintillion) | ≈7.21e+1 (72.1 quadrillion) |
| /9 | ≈6.65e+17 (664613997892457984.0 quintillion) | ≈3.60e+1 (36.0 quadrillion) |
| /10 | ≈3.32e+17 (332306998946228992.0 quintillion) | ≈1.80e+1 (18.0 quadrillion) |
| /11 | ≈1.66e+17 (166153499473114496.0 quintillion) | ≈9.01e+0 (9.0 quadrillion) |
| /12 | ≈8.31e+16 (83076749736557248.0 quintillion) | ≈4.50e+0 (4.5 quadrillion) |
| /13 | ≈4.15e+16 (41538374868278624.0 quintillion) | ≈2.25e+0 (2.3 quadrillion) |
| /14 | ≈2.08e+16 (20769187434139312.0 quintillion) | ≈1.13e+0 (1.1 quadrillion) |
| /15 | ≈1.04e+16 (10384593717069656.0 quintillion) | ≈5.63e+2 (562.9 trillion) |
| /16 | ≈5.19e+15 (5192296858534828.0 quintillion) | ≈2.81e+2 (281.5 trillion) |
| /17 | ≈2.60e+15 (2596148429267414.0 quintillion) | ≈1.41e+2 (140.7 trillion) |
| /18 | ≈1.30e+15 (1298074214633707.0 quintillion) | ≈7.04e+1 (70.4 trillion) |
| /19 | ≈6.49e+14 (649037107316853.5 quintillion) | ≈3.52e+1 (35.2 trillion) |
| /20 | ≈3.25e+14 (324518553658426.8 quintillion) | ≈1.76e+1 (17.6 trillion) |
| /21 | ≈1.62e+14 (162259276829213.4 quintillion) | ≈8.80e+0 (8.8 trillion) |
| /22 | ≈8.11e+13 (81129638414606.7 quintillion) | ≈4.40e+0 (4.4 trillion) |
| /23 | ≈4.06e+13 (40564819207303.3 quintillion) | ≈2.20e+0 (2.2 trillion) |
| /24 | ≈2.03e+13 (20282409603651.7 quintillion) | ≈1.10e+0 (1.1 trillion) |
| /25 | ≈1.01e+13 (10141204801825.8 quintillion) | ≈5.50e+2 (549.8 billion) |
| /26 | ≈5.07e+12 (5070602400912.9 quintillion) | ≈2.75e+2 (274.9 billion) |
| /27 | ≈2.54e+12 (2535301200456.5 quintillion) | ≈1.37e+2 (137.4 billion) |
| /28 | ≈1.27e+12 (1267650600228.2 quintillion) | ≈6.87e+1 (68.7 billion) |
| /29 | ≈6.34e+11 (633825300114.1 quintillion) | ≈3.44e+1 (34.4 billion) |
| /30 | ≈3.17e+11 (316912650057.1 quintillion) | ≈1.72e+1 (17.2 billion) |
| /31 | ≈1.58e+11 (158456325028.5 quintillion) | ≈8.59e+0 (8.6 billion) |
| /32 | ≈7.92e+10 (79228162514.3 quintillion) | ≈4.29e+0 (4.3 billion) |
| /33 | ≈3.96e+10 (39614081257.1 quintillion) | ≈2.15e+0 (2.1 billion) |
| /34 | ≈1.98e+10 (19807040628.6 quintillion) | ≈1.07e+0 (1.1 billion) |
| /35 | ≈9.90e+9 (9903520314.3 quintillion) | 536,870,912 |
| /36 | ≈4.95e+9 (4951760157.1 quintillion) | 268,435,456 |
| /37 | ≈2.48e+9 (2475880078.6 quintillion) | 134,217,728 |
| /38 | ≈1.24e+9 (1237940039.3 quintillion) | 67,108,864 |
| /39 | ≈6.19e+8 (618970019.6 quintillion) | 33,554,432 |
| /40 | ≈3.09e+8 (309485009.8 quintillion) | 16,777,216 |
| /41 | ≈1.55e+8 (154742504.9 quintillion) | 8,388,608 |
| /42 | ≈7.74e+7 (77371252.5 quintillion) | 4,194,304 |
| /43 | ≈3.87e+7 (38685626.2 quintillion) | 2,097,152 |
| /44 | ≈1.93e+7 (19342813.1 quintillion) | 1,048,576 |
| /45 | ≈9.67e+6 (9671406.6 quintillion) | 524,288 |
| /46 | ≈4.84e+6 (4835703.3 quintillion) | 262,144 |
| /47 | ≈2.42e+6 (2417851.6 quintillion) | 131,072 |
| /48 | ≈1.21e+6 (1208925.8 quintillion) | 65,536 |
| /49 | ≈6.04e+5 (604462.9 quintillion) | 32,768 |
| /50 | ≈3.02e+5 (302231.5 quintillion) | 16,384 |
| /51 | ≈1.51e+5 (151115.7 quintillion) | 8,192 |
| /52 | ≈7.56e+4 (75557.9 quintillion) | 4,096 |
| /53 | ≈3.78e+4 (37778.9 quintillion) | 2,048 |
| /54 | ≈1.89e+4 (18889.5 quintillion) | 1,024 |
| /55 | ≈9.44e+3 (9444.7 quintillion) | 512 |
| /56 | ≈4.72e+3 (4722.4 quintillion) | 256 |
| /57 | ≈2.36e+3 (2361.2 quintillion) | 128 |
| /58 | ≈1.18e+3 (1180.6 quintillion) | 64 |
| /59 | ≈5.90e+2 (590.3 quintillion) | 32 |
| /60 | ≈2.95e+2 (295.1 quintillion) | 16 |
| /61 | ≈1.48e+2 (147.6 quintillion) | 8 |
| /62 | ≈7.38e+1 (73.8 quintillion) | 4 |
| /63 | ≈3.69e+1 (36.9 quintillion) | 2 |
| /64 | ≈1.84e+1 (18.4 quintillion) | 1 |
| /65 | ≈9.22e+0 (9.2 quintillion) | - |
| /66 | ≈4.61e+0 (4.6 quintillion) | - |
| /67 | ≈2.31e+0 (2.3 quintillion) | - |
| /68 | ≈1.15e+0 (1.2 quintillion) | - |
| /69 | ≈5.76e+2 (576.5 quadrillion) | - |
| /70 | ≈2.88e+2 (288.2 quadrillion) | - |
| /71 | ≈1.44e+2 (144.1 quadrillion) | - |
| /72 | ≈7.21e+1 (72.1 quadrillion) | - |
| /73 | ≈3.60e+1 (36.0 quadrillion) | - |
| /74 | ≈1.80e+1 (18.0 quadrillion) | - |
| /75 | ≈9.01e+0 (9.0 quadrillion) | - |
| /76 | ≈4.50e+0 (4.5 quadrillion) | - |
| /77 | ≈2.25e+0 (2.3 quadrillion) | - |
| /78 | ≈1.13e+0 (1.1 quadrillion) | - |
| /79 | ≈5.63e+2 (562.9 trillion) | - |
| /80 | ≈2.81e+2 (281.5 trillion) | - |
| /81 | ≈1.41e+2 (140.7 trillion) | - |
| /82 | ≈7.04e+1 (70.4 trillion) | - |
| /83 | ≈3.52e+1 (35.2 trillion) | - |
| /84 | ≈1.76e+1 (17.6 trillion) | - |
| /85 | ≈8.80e+0 (8.8 trillion) | - |
| /86 | ≈4.40e+0 (4.4 trillion) | - |
| /87 | ≈2.20e+0 (2.2 trillion) | - |
| /88 | ≈1.10e+0 (1.1 trillion) | - |
| /89 | ≈5.50e+2 (549.8 billion) | - |
| /90 | ≈2.75e+2 (274.9 billion) | - |
| /91 | ≈1.37e+2 (137.4 billion) | - |
| /92 | ≈6.87e+1 (68.7 billion) | - |
| /93 | ≈3.44e+1 (34.4 billion) | - |
| /94 | ≈1.72e+1 (17.2 billion) | - |
| /95 | ≈8.59e+0 (8.6 billion) | - |
| /96 | ≈4.29e+0 (4.3 billion) | - |
| /97 | ≈2.15e+0 (2.1 billion) | - |
| /98 | ≈1.07e+0 (1.1 billion) | - |
| /99 | 536,870,912 | - |
| /100 | 268,435,456 | - |
| /101 | 134,217,728 | - |
| /102 | 67,108,864 | - |
| /103 | 33,554,432 | - |
| /104 | 16,777,216 | - |
| /105 | 8,388,608 | - |
| /106 | 4,194,304 | - |
| /107 | 2,097,152 | - |
| /108 | 1,048,576 | - |
| /109 | 524,288 | - |
| /110 | 262,144 | - |
| /111 | 131,072 | - |
| /112 | 65,536 | - |
| /113 | 32,768 | - |
| /114 | 16,384 | - |
| /115 | 8,192 | - |
| /116 | 4,096 | - |
| /117 | 2,048 | - |
| /118 | 1,024 | - |
| /119 | 512 | - |
| /120 | 256 | - |
| /121 | 128 | - |
| /122 | 64 | - |
| /123 | 32 | - |
| /124 | 16 | - |
| /125 | 8 | - |
| /126 | 4 | - |
| /127 | 2 | - |
| /128 | 1 | - |
/64 is the standard subnet boundary - don't subnet below this for best compatibility
About IPv6 CIDR Notation
IPv6 CIDR notation works similarly to IPv4, using a prefix length to indicate the network portion of the address. However, IPv6 uses 128 bits instead of 32 bits, allowing for vastly larger address spaces.
Understanding IPv6 Prefix Lengths
- • IPv6 addresses are 128 bits long (vs 32 bits in IPv4)
- • The prefix indicates how many bits are used for the network
- • For example, 2001:db8::/32 means:
- - The first 32 bits are the network portion
- - The remaining 96 bits are available for subnets and hosts
- - This allows for 2^96 addresses
Standard IPv6 Allocation Sizes
- • /32: Typically allocated to ISPs by Regional Internet Registries (RIRs)
- • /48: Standard site allocation (recommended for organizations)
- • /56: Common for residential/small business (some ISPs)
- • /64: Single subnet (the standard subnet size)
- • /128: Single host address
The /64 Boundary
The /64 prefix length is special in IPv6:
- • It's the standard subnet size for IPv6 networks
- • SLAAC (Stateless Address Autoconfiguration) requires /64
- • Dividing below /64 breaks some IPv6 features
- • Each /64 subnet contains 2^64 (18.4 quintillion) addresses
- • Don't use prefixes longer than /64 for end subnets
IPv6 Address Types and Ranges
Global Unicast (2000::/3)
Public IPv6 addresses routable on the Internet. Currently, most allocations come from 2000::/3. This is the IPv6 equivalent of public IPv4 addresses.
Unique Local Addresses (fc00::/7)
Private IPv6 addresses (similar to 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 in IPv4). Not routable on the global Internet. fd00::/8 is commonly used.
Link-Local (fe80::/10)
Automatically configured on all IPv6 interfaces. Only valid on a single link (not routed). Required for IPv6 to function.
Documentation (2001:db8::/32)
Reserved for documentation and examples. Never routed on the Internet. Use this range in documentation, not real addresses.
Why IPv6 Networks Are So Large
Unlike IPv4 where we conserve addresses, IPv6 design philosophy is:
- • Allocate generously (no address scarcity)
- • Simplify network design (no NAT needed)
- • Enable address stability (no need to renumber)
- • Support new features (privacy addresses, multiple addresses per interface)
Common IPv6 Prefix Examples
- • 2001:db8::/32 - Documentation network
- • 2001:db8:1234::/48 - Organization site
- • 2001:db8:1234:5600::/56 - Department or building
- • 2001:db8:1234:5678::/64 - Single subnet (e.g., a VLAN)
- • 2001:db8:1234:5678::1/128 - Single host
Subnetting Guidelines
- • Always use /64 for end subnets (don't go below /64)
- • /48 provides 65,536 /64 subnets (enough for most organizations)
- • /56 provides 256 /64 subnets (suitable for homes/small sites)
- • Plan your addressing hierarchy before deployment
- • Reserve ranges for future growth
Reading the Table
- • Prefix: The prefix length (/0 to /128)
- • Total Addresses: All possible addresses in the range (2^(128-prefix))
- • Total /64 Subnets: How many /64 subnets fit (only shown for prefixes < /64)
- • Numbers are shown in scientific notation for readability
- • Highlighted rows indicate commonly used prefix lengths