IPv6 subnet calculator
Enter an IPv6 prefix to see the full and compressed form, the number of /64 networks and how the prefix splits up. Add a MAC address to work out the EUI-64 address.
Result: 2001:db8:abcd::/48
- Compressed form
- 2001:db8:abcd::/48
- Full form
- 2001:0db8:abcd:0000:0000:0000:0000:0000/48
- First usable address
- 2001:db8:abcd::
- Last usable address
- 2001:db8:abcd:ffff:ffff:ffff:ffff:ffff
- Number of addresses
- 1,208,925,819,614,629,174,706,176
- Number of /64 networks
- 65,536
- Address type
- Documentation (examples only)
- Reverse DNS zone
- d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa
Split into /64
| Network | Reverse DNS zone |
|---|---|
| 2001:db8:abcd::/64 | 0.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:1::/64 | 1.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:2::/64 | 2.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:3::/64 | 3.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:4::/64 | 4.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:5::/64 | 5.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:6::/64 | 6.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:7::/64 | 7.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:8::/64 | 8.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:9::/64 | 9.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:a::/64 | a.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:b::/64 | b.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:c::/64 | c.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:d::/64 | d.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:e::/64 | e.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
| 2001:db8:abcd:f::/64 | f.0.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa |
Showing the first 16 of 65,536.
Generate a ULA prefix
Unique local addresses (fd00::/8) are the IPv6 answer to private addresses. The prefix should contain a random 40-bit global ID, so two organisations almost never end up with the same prefix.
Common IPv6 prefixes
| Prefix | Typical use | Number of /64 networks |
|---|---|---|
| /32 | Allocation to an ISP or large organisation (LIR) | 4,294,967,296 |
| /48 | One site or a medium-sized organisation | 65,536 |
| /56 | Smaller site, business or residential customer | 256 |
| /60 | Smallest common residential assignment | 16 |
| /64 | One LAN (VLAN). Required for SLAAC | 1 |
| /127 | Point-to-point link between routers (RFC 6164) | – |
| /128 | A single address, such as a loopback | – |
Why is everything /64?
In IPv6 the last 64 bits of an address are the interface ID. Stateless address autoconfiguration (SLAAC) and many other mechanisms assume the LAN is exactly a /64. That gives 18 quintillion addresses per network – you will never run out, and you should not try to save addresses by using smaller networks for clients.
Split on nibble boundaries
An IPv6 address is written in hexadecimal, where each character is 4 bits – a *nibble*. Split the prefix in 4-bit steps (/48 → /52 → /56 → /60 → /64) and each level appears as its own character in the address. That keeps the plan readable and reverse DNS simple, because ip6.arpa is also split per nibble.
| From | To | Count | Example |
|---|---|---|---|
| /48 | /52 | 16 | One per building or zone |
| /48 | /56 | 256 | One per floor or department |
| /48 | /64 | 65,536 | One per VLAN |
| /56 | /64 | 256 | One per VLAN at a smaller site |
Use the VLAN number in the address
A /48 leaves 16 bits for the subnet ID – four hexadecimal characters. Write the VLAN number straight in and VLAN 110 becomes 2001:db8:abcd:110::/64. It is not mathematically “correct” (decimal 110 is not 0x110), but it is easy to read, which is what matters in operations. ipmanager uses this method in its IPv6 plan.
EUI-64 and privacy
With EUI-64 the interface ID is derived from the MAC address: bit 7 of the first byte is flipped and ff:fe is inserted in the middle. The address becomes predictable, which is handy for servers and network gear but bad for client privacy. Modern clients therefore use random, or stable but not MAC-based, IDs.
Read more in the guide IPv6 in practice.
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