IPv6 Subnet Calculator

Expand or compress any IPv6 address, inspect its prefix and type, count addresses and /64 subnets — instantly and server-side.

Results for 2001:db8::/48

2001:db8::/48 is the network in CIDR notation · Documentation (RFC 3849)

Fully expanded form: 2001:0db8:0000:0000:0000:0000:0000:0000
Compressed form (RFC 5952): 2001:db8::
Prefix length: /48
Type: Documentation (RFC 3849)
Total addresses: 1,208,925,819,614,629,174,706,176
/64 subnets inside: 65,536
First address of prefix: 2001:db8::
Last address of prefix: 2001:db8:0:ffff:ffff:ffff:ffff:ffff
Network in CIDR notation: 2001:db8::/48

Keep exploring IPv6

Reference pages for the most common allocations: IPv6 /32 IPv6 /48 IPv6 /56 IPv6 /64

Working with IPv6 prefixes

An IPv6 address is 128 bits long and written as eight hexadecimal groups. Any single run of all-zero groups can be squeezed into ::, which is why 2001:0db8:0000:0000:0000:0000:0000:0001 and 2001:db8::1 are the same address. A prefix written with a slash (“/48”) fixes that many leading bits, leaving the rest for subnets and hosts.

The /64 boundary is special. Interface identifiers are 64 bits wide, so a /64 is the standard subnet size — the smallest prefix that supports SLAAC, the mechanism that lets hosts configure their own addresses from router advertisements. Networks are therefore planned hierarchically: an ISP holds a /32, hands each customer site a /48 or /56, and every LAN inside it becomes one /64 containing 18 quintillion addresses.

Special ranges to know: 2001:db8::/32 is reserved for documentation (RFC 3849), fe80::/10 is link-local, fc00::/7 holds unique-local addresses, and ::1 is loopback — this tool labels them automatically.