More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown
Neighboring /0 subnets
- Expanded address
- Compressed address
- Network (expanded)
- Last address (expanded)
- Prefix mask
- Total addresses (exact)
- Reverse DNS (PTR)
- Host bits / network bits
Hextet breakdown
20000000000000000000000000000000
NetworkSplit groupHost
Quick facts for IPv6 /0
- Prefix mask: ::
- Total addresses: 2¹²⁸
- Approx. count: 3.40 × 10³⁸
- /64 subnets: 2⁶⁴
IPv6 /0 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ
Network / host bit split
hosthosthosthosthosthosthosthost
Network bits (0)Split hextetHost bits (128)
- Network bits
- 0
- Host bits
- 128
- Prefix mask
- ::
- Total addresses
- 2¹²⁸
- Approx. count
- 3.40 × 10³⁸
- /64 subnets
- 2⁶⁴
- Addresses formula
- 2^128
- /64 relationship
- 2⁶⁴ × /64 subnets
Overview
A /0 is the IPv6 default route — it matches every possible 128-bit address. Like 0.0.0.0/0 in IPv4, it appears in routing tables as the catch-all when no more specific route exists. It is never assigned to a network interface.
Common use cases
- Default route (::/0) in routing tables
- Catch-all firewall and policy rules
- VPN full-tunnel default routing
Key facts
- A /0 fixes 0 network bits and leaves 128 host bits — 2¹²⁸ total addresses.
- In network design terms, /0 is typically a default route.
- You can subnet a /0 into about 2⁶⁴ /64 LANs.
- At site scale, /0 equals about 2⁴⁸ /48 allocations.
- At ISP scale, /0 contains about 2³² /32 blocks.
Design guidance
Use /0 only in routing tables and firewall policies as a default route. Never assign it to an interface. In split-tunnel VPN designs, some clients install two /1 routes instead of a single /0 to avoid overriding the physical default gateway.
Practical example
A default route entry looks like `::/0 via 2001:db8::1` on a router — it matches every IPv6 destination not covered by a more specific route.
Related RFCs and standards
- RFC 4291IPv6 Addressing Architecture
- RFC 3849IPv6 Documentation Address Prefix (2001:db8::/32)
Prefix sizing reference
Notable /0 networks
::/0Default route — entire IPv6 space2000::/3Global unicast — all public IPv6 today2001:db8::/32Documentation prefix (RFC 3849)
Frequently asked questions
Common questions about IPv6 /0 blocks, prefix sizes, and use cases.