IPv6 Connectivity Checker
Inspect 128-bit IPv6 address formatting, decompose all eight 16-bit hexadecimal segments (hextets), compare RFC 5952 compressed and expanded representations, and understand dual-stack IPv6 behavior in India.
Canonical RFC 5952 Zero-Compressed IPv6 Address
2405:200:1601::1
Expanded 128-bit form: 2405:0200:1601:0000:0000:0000:0000:0001
Eight 16-Bit Hexadecimal Segments (Hextets · 8 × 16 bits = 128 bits)
Hextets 1–4: 64-bit Routing Prefix · Hextets 5–8: 64-bit Interface Identifier (IID)
H1 · Prefix
2405
Dec: 9221
H2 · Prefix
0200
Dec: 512
H3 · Prefix
1601
Dec: 5633
H4 · Prefix
0000
Dec: 0
H5 · IID
0000
Dec: 0
H6 · IID
0000
Dec: 0
H7 · IID
0000
Dec: 0
H8 · IID
0001
Dec: 1
IANA IPv6 Scope & Classification
Global Unicast IPv6 Address (GUA)
RFC 4291 / RFC 3587 · Prefix Block: 2000::/3
32-Nibble Reverse DNS Zone (ip6.arpa)
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.6.1.0.0.2.0.5.0.4.2.ip6.arpa
Understanding 128-Bit IPv6 Addressing and Dual-Stack Fallback
IPv6 (standardized in IETF RFC 8200 and RFC 4291) expands the internet address width from 32 bits to 128 bits, written as eight 16-bit hexadecimal groups separated by colons. Under RFC 5952 canonical rules, leading zeros inside each 16-bit group are omitted and the single longest run of all-zero hextets is compressed to ::.
On dual-stack networks, modern browsers use the Happy Eyeballs algorithm (RFC 8305): they race IPv6 (AAAA) and IPv4 (A) connection attempts in parallel and use whichever completes the TCP/TLS handshake first. If a reverse proxy or container ingress accepts traffic over IPv4 or dual-stack, the server observes whichever address family won that connection race. Read our research brief on IPv6 Deployment in India for APNIC measurement details.
Common IPv6 Address Prefixes
- 2000::/3 — Global Unicast Addresses (GUA) routed on the public internet (including APNIC's 2400::/12 block used across India).
- fe80::/10 — Link-Local Unicast configured automatically on every network interface for local neighbor discovery.
- fc00::/7 — Unique Local Addresses (ULA, RFC 4193) for private internal routing.
Technical Specifications & Protocol Facts
Authoritative parameters, dimensions, and IETF RFC compliance
| Parameter / Dimension | Technical Specification | Standard / Authority |
|---|---|---|
| Address Bit Length | 128 bits (16 bytes) written as 8 hexadecimal hextets (0000–ffff) | RFC 8200 / RFC 4291 |
| Canonical Text Representation | Lowercase hex, leading zeros stripped, longest zero-run compressed as :: | RFC 5952 |
| Global Unicast Prefix | 2000::/3 (initial hex digit 2 or 3) | IANA IPv6 GUA |
| Local & Link Scopes | fe80::/10 (Link-Local) & fc00::/7 (Unique Local Address ULA) | RFC 4291 / RFC 4193 |
Frequently Asked Questions
Concise answers verified against IANA, APNIC, and IETF protocol standards
Why might my connection show IPv4-only on this server check even if my ISP supports IPv6?
Dual-stack browsers use Happy Eyeballs (RFC 8305) to race IPv6 and IPv4 connections, and intermediate edge proxies may terminate over IPv4. You can also paste any IPv6 address into the inspector below.
What does the double colon (::) mean inside an IPv6 address?
Per RFC 5952, a single double colon (::) compresses the longest contiguous sequence of all-zero 16-bit hextets so long 128-bit IPv6 addresses remain compact and readable.
Why does India have one of the highest IPv6 adoption rates in the world?
Major Indian 4G/5G mobile carriers and fiber ISPs built modern greenfield networks using native dual-stack IPv6 global unicast addressing alongside IPv4 CGNAT.
Related Network Tools & Technical Guides
Contextual utilities and reference documentation verified for this workflow
Diagnostic & Calculation Utilities
- IPv4 Checker
Inspect the visitor IPv4 address observed by the server, octet breakdown, and RFC 1918 / RFC 6598 CGNAT status.
- IP Address Validator & Classifier
Verify syntactic validity and inspect whether an IP is globally routable or reserved in an IANA special-purpose block.
- IP Address Converter
Convert IPv4 and IPv6 addresses across canonical, expanded, decimal integer, hexadecimal, binary, and reverse ARPA forms.
Technical Reference Guides
- IPv4 vs IPv6
Technical comparison of 32-bit dotted-decimal IPv4 and 128-bit hexadecimal IPv6 packet addressing.
- IPv6 Adoption in India
Understand APNIC Labs measurement methodology, Indian dual-stack mobile architecture, and how to test IPv6.
- What Is CGNAT?
Understand RFC 6598 100.64.0.0/10 shared address space, double NAT, port forwarding limits, and IPv6 alternatives.
IPv6 Checker · Canonical: https://ipaddresslookup.in/ipv6-check · Reviewed: 2026-11-01
Reviewer: IPAddressLookup.in Technical Network Utility Group · Stateless Privacy · Accuracy & Data Limits