What is my IPv6 subnet range?

How it works

An IPv6 address is a 128-bit number. A prefix length p (0 to 128) says how many leading bits are the network part.

• mask = p one bits followed by 128 − p zero bits
• network address = address AND mask (every host bit set to 0)
• last address = network OR (NOT mask) (every host bit set to 1)
• addresses = 2^(128 − p)
• /64 subnets = 2^(64 − p), shown only when p is 64 or less

Reading the address

The address may be typed in any text form of RFC 4291, section 2.2:

• eight groups of 1 to 4 hex digits separated by colons, in any case, with or without leading zeros (2001:0DB8:0:0:8:800:200C:417A);
• with :: once, standing for one or more zero groups (2001:db8::1);
• with the last 32 bits as an IPv4 dotted quad (::ffff:192.0.2.128); each of its four numbers is 0 to 255 with no leading zeros.

A prefix may follow a slash (2001:db8::1/48). It must be a whole number from 0 to 128 with no leading zeros. Without a slash, the Prefix length field is used (default /64). A second slash (::1/64/2) gives the prefix message below once the address itself reads. Zone indexes (%eth0) are not accepted. Any other text gives no answer, with one of these messages:

• "Enter an IPv6 address as up to eight groups of 1 to 4 hex digits separated by colons, with :: for one run of zero groups, such as 2001:db8::1."
• "Use :: only once in an address."
• "The prefix after the slash must be a whole number from 0 to 128."

The text may be up to 49 characters long, counting any spaces before and after it; those spaces are then ignored. A :: must stand for at least one zero group, so an address with eight groups and a :: has no answer.

Writing the results

Every address in the results is written in the RFC 5952 form: lowercase hex, no leading zeros in a group, and :: in place of the longest run of two or more consecutive zero groups. When two runs are equally long, the first is shortened. A lone zero group is written 0. Results are always written in hex groups, so an IPv4-mapped address shows as ::ffff:c000:280, not with a dotted quad.

• Network: the network address, a slash and p.
• Address range: the network address, a spaced en dash ( – ), and the last address; a /128 shows the one address.
• Addresses: 2^(128 − p) written in full with commas between groups of three digits.
• Addresses as a power of 2: the text 2^ followed by 128 − p, such as 2^64.
• /64 subnets: 2^(64 − p) with commas, for p from 0 to 64; not shown for longer prefixes.
• Full address: the address typed (not the network), as eight groups of exactly four lowercase hex digits.
• Compressed address: the address typed, in the RFC 5952 form.
• Address type: the first block in this list that holds the typed address:

Any other address is "Other (reserved or unassigned)".

Worked examples by hand

2001:db8:abcd:12::1 on a /64. The first four groups are the network part: 2001:db8:abcd:12. Setting the last four groups to 0 gives the network 2001:db8:abcd:12::/64, and setting them to ffff gives the last address 2001:db8:abcd:12:ffff:ffff:ffff:ffff. Addresses: 2^64 = 18,446,744,073,709,551,616, and the /64 count is 2^0 = 1. The full address is 2001:0db8:abcd:0012:0000:0000:0000:0001. It is in 2001:db8::/32, so its type is Documentation.

2001:0DB8:0000:0000:0001:0000:0000:0001/48. The groups are 2001, db8, 0, 0, 1, 0, 0, 1. Its compressed form has two runs of two zero groups; the first is shortened: 2001:db8::1:0:0:1 (the RFC 5952 example). Keeping the first 48 bits (three groups) gives 2001:db8::/48, and the last address is 2001:db8:0:ffff:ffff:ffff:ffff:ffff. Addresses: 2^80 = 1,208,925,819,614,629,174,706,176, which is 2^16 = 65,536 subnets of /64.

fe80::1ff:fe23:4567:890a on a /10. The first group fe80 is 1111 1110 1000 0000; its first 10 bits are kept, so the network is fe80::/10 and the last address is febf:ffff:ffff:ffff:ffff:ffff:ffff:ffff. Type: Link-local unicast.

2001:db8:0:1:1:1:1:1 on a /128. There is only one zero group, so no :: is used. The subnet is that one address: range 2001:db8:0:1:1:1:1:1, 1 address, no /64 count.

::ffff:192.0.2.128/96. The dotted quad is the last 32 bits: 192 = c0, 0 = 00, 2 = 02, 128 = 80, so the groups are 0, 0, 0, 0, 0, ffff, c000, 0280. Keeping 96 bits gives ::ffff:0:0/96 with 2^32 = 4,294,967,296 addresses. Type: IPv4-mapped.