subnetting — ipv6
A shortcut for subnetting IPv6
IPv6 addresses are 128 bits, split into common prefix boundaries. Here's where they fall, and how the address space scales at each one.
/16 /32 /48 /64 /80 /96 /112
v v v v v v v
2001:aaaa:bbbb:cccc:dddd:eeee:ffff:1111
/48 — the site allocation
The typical assignment for an end site — an organization, a home, a single customer. Contains 65,536 /64s to work with.
/56 — the small-site allocation
Common for residential and small-business assignments — 256 /64 subnets, still vastly more than almost anyone needs.
/64 — the subnet
The standard subnet size for a single link. Not a suggestion — SLAAC and most of the IPv6 addressing architecture assume /64 on every subnet.
Everything shorter
Prefixes shorter than /48 are the province of registries and ISPs — allocations for entire organizations' worth of /48s and /56s downstream.
| Prefix | /48 count | /56 count | /64 subnets | Number of addresses | ≈ scale |
|---|---|---|---|---|---|
| /64 | — | — | 1 | 18,446,744,073,709,551,616 | 18.4 quintillion |
| /63 | — | — | 2 | 36,893,488,147,419,103,232 | 36.9 quintillion |
| /62 | — | — | 4 | 73,786,976,294,838,206,464 | 73.8 quintillion |
| /61 | — | — | 8 | 147,573,952,589,676,412,928 | 147.6 quintillion |
| /60 | — | — | 16 | 295,147,905,179,352,825,856 | 295.1 quintillion |
| /59 | — | — | 32 | 590,295,810,358,705,651,712 | 590.3 quintillion |
| /58 | — | — | 64 | 1,180,591,620,717,411,303,424 | 1.2 sextillion |
| /57 | — | — | 128 | 2,361,183,241,434,822,606,848 | 2.4 sextillion |
| /56 | — | 1 | 256 | 4,722,366,482,869,645,213,696 | 4.7 sextillion |
| /55 | — | 2 | 512 | 9,444,732,965,739,290,427,392 | 9.4 sextillion |
| /54 | — | 4 | 1,024 | 18,889,465,931,478,580,854,784 | 18.9 sextillion |
| /53 | — | 8 | 2,048 | 37,778,931,862,957,161,709,568 | 37.8 sextillion |
| /52 | — | 16 | 4,096 | 75,557,863,725,914,323,419,136 | 75.6 sextillion |
| /51 | — | 32 | 8,192 | 151,115,727,451,828,646,838,272 | 151.1 sextillion |
| /50 | — | 64 | 16,384 | 302,231,454,903,657,293,676,544 | 302.2 sextillion |
| /49 | — | 128 | 32,768 | 604,462,909,807,314,587,353,088 | 604.5 sextillion |
| /48 | 1 | 256 | 65,536 | 1,208,925,819,614,629,174,706,176 | 1.2 septillion |
| /47 | 2 | 512 | 131,072 | 2,417,851,639,229,258,349,412,352 | 2.4 septillion |
| /46 | 4 | 1,024 | 262,144 | 4,835,703,278,458,516,698,824,704 | 4.8 septillion |
| /45 | 8 | 2,048 | 524,288 | 9,671,406,556,917,033,397,649,408 | 9.7 septillion |
| /44 | 16 | 4,096 | 1,048,576 | 19,342,813,113,834,066,795,298,816 | 19.3 septillion |
| /43 | 32 | 8,192 | 2,097,152 | 38,685,626,227,668,133,590,597,632 | 38.7 septillion |
| /42 | 64 | 16,384 | 4,194,304 | 77,371,252,455,336,267,181,195,264 | 77.4 septillion |
| /41 | 128 | 32,768 | 8,388,608 | 154,742,504,910,672,534,362,390,528 | 154.7 septillion |
| /40 | 256 | 65,536 | 16,777,216 | 309,485,009,821,345,068,724,781,056 | 309.5 septillion |
| /39 | 512 | 131,072 | 33,554,432 | 618,970,019,642,690,137,449,562,112 | 619.0 septillion |
| /38 | 1,024 | 262,144 | 67,108,864 | 1,237,940,039,285,380,274,899,124,224 | 1.2 octillion |
| /37 | 2,048 | 524,288 | 134,217,728 | 2,475,880,078,570,760,549,798,248,448 | 2.5 octillion |
| /36 | 4,096 | 1,048,576 | 268,435,456 | 4,951,760,157,141,521,099,596,496,896 | 5.0 octillion |
| /35 | 8,192 | 2,097,152 | 536,870,912 | 9,903,520,314,283,042,199,192,993,792 | 9.9 octillion |
| /34 | 16,384 | 4,194,304 | 1,073,741,824 | 19,807,040,628,566,084,398,385,987,584 | 19.8 octillion |
| /33 | 32,768 | 8,388,608 | 2,147,483,648 | 39,614,081,257,132,168,796,771,975,168 | 39.6 octillion |
| /32 | 65,536 | 16,777,216 | 4,294,967,296 | 79,228,162,514,264,337,593,543,950,336 | 79.2 octillion |
| /31 | 131,072 | 33,554,432 | 8,589,934,592 | 158,456,325,028,528,675,187,087,900,672 | 158.5 octillion |
| /30 | 262,144 | 67,108,864 | 17,179,869,184 | 316,912,650,057,057,350,374,175,801,344 | 316.9 octillion |
| /29 | 524,288 | 134,217,728 | 34,359,738,368 | 633,825,300,114,114,700,748,351,602,688 | 633.8 octillion |
| /28 | 1,048,576 | 268,435,456 | 68,719,476,736 | 1,267,650,600,228,229,401,496,703,205,376 | 1.3 nonillion |
| /27 | 2,097,152 | 536,870,912 | 137,438,953,472 | 2,535,301,200,456,458,802,993,406,410,752 | 2.5 nonillion |
| /26 | 4,194,304 | 1,073,741,824 | 274,877,906,944 | 5,070,602,400,912,917,605,986,812,821,504 | 5.1 nonillion |
| /25 | 8,388,608 | 2,147,483,648 | 549,755,813,888 | 10,141,204,801,825,835,211,973,625,643,008 | 10.1 nonillion |
| /24 | 16,777,216 | 4,294,967,296 | 1,099,511,627,776 | 20,282,409,603,651,670,423,947,251,286,016 | 20.3 nonillion |
| /23 | 33,554,432 | 8,589,934,592 | 2,199,023,255,552 | 40,564,819,207,303,340,847,894,502,572,032 | 40.6 nonillion |
| /22 | 67,108,864 | 17,179,869,184 | 4,398,046,511,104 | 81,129,638,414,606,681,695,789,005,144,064 | 81.1 nonillion |
| /21 | 134,217,728 | 34,359,738,368 | 8,796,093,022,208 | 162,259,276,829,213,363,391,578,010,288,128 | 162.3 nonillion |
| /20 | 268,435,456 | 68,719,476,736 | 17,592,186,044,416 | 324,518,553,658,426,726,783,156,020,576,256 | 324.5 nonillion |
| /19 | 536,870,912 | 137,438,953,472 | 35,184,372,088,832 | 649,037,107,316,853,453,566,312,041,152,512 | 649.0 nonillion |
| /18 | 1,073,741,824 | 274,877,906,944 | 70,368,744,177,664 | 1,298,074,214,633,706,907,132,624,082,305,024 | 1.3 decillion |
| /17 | 2,147,483,648 | 549,755,813,888 | 140,737,488,355,328 | 2,596,148,429,267,413,814,265,248,164,610,048 | 2.6 decillion |
| /16 | 4,294,967,296 | 1,099,511,627,776 | 281,474,976,710,656 | 5,192,296,858,534,827,628,530,496,329,220,096 | 5.2 decillion |
| /15 | 8,589,934,592 | 2,199,023,255,552 | 562,949,953,421,312 | 10,384,593,717,069,655,257,060,992,658,440,192 | 10.4 decillion |
| /14 | 17,179,869,184 | 4,398,046,511,104 | 1,125,899,906,842,624 | 20,769,187,434,139,310,514,121,985,316,880,384 | 20.8 decillion |
| /13 | 34,359,738,368 | 8,796,093,022,208 | 2,251,799,813,685,248 | 41,538,374,868,278,621,028,243,970,633,760,768 | 41.5 decillion |
| /12 | 68,719,476,736 | 17,592,186,044,416 | 4,503,599,627,370,496 | 83,076,749,736,557,242,056,487,941,267,521,536 | 83.1 decillion |
| /11 | 137,438,953,472 | 35,184,372,088,832 | 9,007,199,254,740,992 | 166,153,499,473,114,484,112,975,882,535,043,072 | 166.2 decillion |
| /10 | 274,877,906,944 | 70,368,744,177,664 | 18,014,398,509,481,984 | 332,306,998,946,228,968,225,951,765,070,086,144 | 332.3 decillion |
| /9 | 549,755,813,888 | 140,737,488,355,328 | 36,028,797,018,963,968 | 664,613,997,892,457,936,451,903,530,140,172,288 | 664.6 decillion |
| /8 | 1,099,511,627,776 | 281,474,976,710,656 | 72,057,594,037,927,936 | 1,329,227,995,784,915,872,903,807,060,280,344,576 | 1.3 undecillion |
| /7 | 2,199,023,255,552 | 562,949,953,421,312 | 144,115,188,075,855,872 | 2,658,455,991,569,831,745,807,614,120,560,689,152 | 2.7 undecillion |
| /6 | 4,398,046,511,104 | 1,125,899,906,842,624 | 288,230,376,151,711,744 | 5,316,911,983,139,663,491,615,228,241,121,378,304 | 5.3 undecillion |
| /5 | 8,796,093,022,208 | 2,251,799,813,685,248 | 576,460,752,303,423,488 | 10,633,823,966,279,326,983,230,456,482,242,756,608 | 10.6 undecillion |
| /4 | 17,592,186,044,416 | 4,503,599,627,370,496 | 1,152,921,504,606,846,976 | 21,267,647,932,558,653,966,460,912,964,485,513,216 | 21.3 undecillion |
| /3 | 35,184,372,088,832 | 9,007,199,254,740,992 | 2,305,843,009,213,693,952 | 42,535,295,865,117,307,932,921,825,928,971,026,432 | 42.5 undecillion |
| /2 | 70,368,744,177,664 | 18,014,398,509,481,984 | 4,611,686,018,427,387,904 | 85,070,591,730,234,615,865,843,651,857,942,052,864 | 85.1 undecillion |
| /1 | 140,737,488,355,328 | 36,028,797,018,963,968 | 9,223,372,036,854,775,808 | 170,141,183,460,469,231,731,687,303,715,884,105,728 | 170.1 undecillion |
| /0 | 281,474,976,710,656 | 72,057,594,037,927,936 | 18,446,744,073,709,551,616 | 340,282,366,920,938,463,463,374,607,431,768,211,456 | 340.3 undecillion |
// /0 is the entire IPv6 address space: 2^128 addresses. Nobody's routing that.