Common IPv6 Prefix Lengths
Quick reference for common IPv6 prefix lengths and their typical uses in network design.
IPv6 Prefix Length Overview
IPv6 uses prefix lengths just like IPv4 CIDR, but the numbers are different due to IPv6's 128-bit address space. Understanding common prefix lengths helps with IPv6 network planning and address allocation. Unlike IPv4 where /24 is common, IPv6 networks typically use /64 for end-user networks and larger prefixes for routing aggregation.
Common IPv6 Prefix Lengths
/128 - Single Host
Capacity: 1 address
Typical Use: Host routes, loopback interfaces
Description: Equivalent to IPv4 /32, identifies one specific address
Examples:
::1/128 - IPv6 loopback
2001:db8::1/128 - Single server
/127 - Point-to-Point Link
Capacity: 2 addresses
Typical Use: Router-to-router links
Description: Saves address space on point-to-point links, like IPv4 /30
Examples:
2001:db8:1:1::/127 - Router link
/64 - Standard Subnet
Capacity: 18,446,744,073,709,551,616 addresses
Typical Use: LAN segments, end-user networks
Description: Standard subnet size, allows SLAAC and EUI-64
Examples:
2001:db8:1::/64 - Office network
fe80::/64 - Link-local
/60 - Small Site
Capacity: 16 /64 subnets
Typical Use: Small offices, residential sites
Description: Provides 16 /64 networks for a small site
Examples:
2001:db8:1000::/60 - Small office allocation
/56 - Typical Site
Capacity: 256 /64 subnets
Typical Use: Medium businesses, large homes
Description: Common allocation for business sites and power users
Examples:
2001:db8:1200::/56 - Business allocation
/48 - Large Site
Capacity: 65,536 /64 subnets
Typical Use: Enterprises, ISP customers
Description: Traditional site allocation, very generous subnet space
Examples:
2001:db8::/48 - Enterprise allocation
/32 - ISP/RIR Allocation
Capacity: 4,294,967,296 /64 subnets
Typical Use: ISPs, large organizations
Description: Minimum allocation from Regional Internet Registries
Examples:
2001:db8::/32 - ISP allocation
Usage Guidelines
Residential/Small Office
/60
Small home with multiple VLANs/networks
/56
Power user or small business
/48
Large home office or small enterprise
Enterprise Networks
/48
Single large site
/44 or /40
Multi-site organization
/32
Large enterprise or ISP
Individual Subnets
/64
Standard LAN segment
/127
Point-to-point router links
/128
Loopbacks, host routes
IPv4 vs IPv6 Comparison
| IPv4 Equivalent | IPv6 Usage | Note |
|---|---|---|
/32 (1 host) | /128 (1 host) | Single host address |
/30 (2 hosts) | /127 (2 hosts) | Point-to-point links |
/24 (254 hosts) | /64 (huge) | LAN segment |
/16 (65k hosts) | /48 (65k subnets) | Large network |
/8 (16M hosts) | /32 (4B subnets) | ISP allocation |
Quick Reference Table
| Prefix | Available /64 Subnets | Typical Use |
|---|---|---|
/32 | 4.3B /64s | RIR minimum allocation |
/40 | 16M /64s | Large enterprise |
/44 | 1M /64s | Medium enterprise |
/48 | 65k /64s | Traditional site |
/52 | 4k /64s | Large site |
/56 | 256 /64s | Typical site |
/60 | 16 /64s | Small site |
/64 | 1 subnet | End-user network |
Best Practices
- Always use /64 for end-user networks (required for SLAAC)
- Use /127 for point-to-point links to save address space
- Plan your addressing hierarchy before assigning prefixes
- Reserve some prefix space for future growth
- Document your prefix allocation scheme
- Use consistent prefix lengths within network tiers
Key Rule
Always use /64 for end-user networks. This is required for SLAAC (Stateless Address Autoconfiguration) and
many IPv6 features.
Planning Tips
Remember These
IPv6 has so much address space that conservation isn't usually necessary
/64 is mandatory for SLAAC (Stateless Address Autoconfiguration)
Shorter prefixes mean more subnets available
Most home users get /60 or /56 from their ISP
Enterprise networks typically start with /48 or shorter
Use nibble boundaries (multiples of 4) for easier management