IPv6 /128 Address Calculator
Calculate single-address IPv6 prefix details.
IPv6 /128 Address Calculator: inputs and results
Enter an IP address, CIDR prefix, or range. Then check its first and last address below.
Calculated Boundaries & ParametersReady
Key Capabilities
- •100% Client-Side: Zero telemetry or server latency.
- •RFC Compliant: Exact 32-bit and 128-bit integer precision.
- •Quick Copy: Instant access to CIDR, mask, and range bounds.
- •Cross-Platform: Works on desktop, tablet, and mobile browsers.
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How IPv6 /128 Address Calculator Works?
This tool works by treating one IPv6 address as a prefix with 128 network bits and 0 interface bits, then returning the full, compressed, and integer forms of that address.
Enter one IPv6 address
Type an address such as
2001:db8::53.Set the prefix to /128
All 128 bits become prefix bits, so the block holds 1 address.
Expand and compress
The calculator prints the full 39-character form and the RFC 5952 compressed form.
Show the route form
The result
2001:db8::53/128is ready for host routes, loopbacks, and firewall objects.
IPv6 /128 Address Calculator Formula
The formula is Network = First = Last = IP, with Count = 2^(128 − 128) = 1.
Mask
2^128 − 1 (all 128 bits set)Written as ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff.
Address count
2^0 = 1A single interface.
Route form
IP/128The most specific IPv6 route.
Worked example: 2001:db8::53
Full = 2001:0db8:0000:0000:0000:0000:0000:0053 Compressed = 2001:db8::53 Prefix = 2001:db8::53/128 Addresses = 1
IPv6 /128 Address Calculator Conversion Table
The table shows 8 sample addresses as /128 host routes, with the expanded form and a common role.
| Host Route | Expanded Form | Common Role |
|---|---|---|
| ::1/128 | 0000:0000:0000:0000:0000:0000:0000:0001 | Loopback |
| 2001:db8::1/128 | 2001:0db8:0000:0000:0000:0000:0000:0001 | Router loopback |
| 2001:db8::53/128 | 2001:0db8:0000:0000:0000:0000:0000:0053 | Anycast DNS |
| 2001:db8:0:1::10/128 | 2001:0db8:0000:0001:0000:0000:0000:0010 | Load balancer VIP |
| 2001:db8:ffff::1/128 | 2001:0db8:ffff:0000:0000:0000:0000:0001 | BGP router ID host |
| fd00::100/128 | fd00:0000:0000:0000:0000:0000:0000:0100 | Internal service (ULA) |
| 2001:db8:dead:beef::1/128 | 2001:0db8:dead:beef:0000:0000:0000:0001 | Blackhole target |
| 2001:4860:4860::8888/128 | 2001:4860:4860:0000:0000:0000:0000:8888 | Public resolver |
What is IPv6 /128 Address Calculator?
The IPv6 /128 Address Calculator is a tool that describes a single IPv6 address as a /128 prefix, the IPv6 equivalent of an IPv4 /32 host route.
A /128 prefix covers exactly 1 address. Routers use /128 entries for loopback interfaces, anycast service addresses, and per-host blackhole routes. The calculator shows the expanded and compressed forms, so the address matches across tools that print it differently.
Longest prefix match always prefers a /128 over any shorter prefix, which makes /128 routes the most precise way to steer or drop traffic for 1 destination.
What are the uses of IPv6 /128 Address Calculator?
There are 4 main uses of the IPv6 /128 Address Calculator, including loopbacks, anycast, and host-specific rules.
Assigning router loopbacks
IPv6 loopback interfaces use /128 addresses for stable BGP and OSPFv3 endpoints.
Advertising anycast services
DNS and CDN operators announce the same /128 from many sites.
Writing host-specific firewall rules
A /128 object permits or blocks 1 server.
Matching logs to inventory
The expanded form matches log files that store full 39-character addresses.