IPv6 PI Allocation Sizes Explained

IPv6 Provider Independent (PI) assignments offer organizations the address space they need for stable, provider-independent networking. Unlike the constrained world of IPv4, IPv6's vast address space allows for generous assignments that can accommodate even large organizational needs. This article explains IPv6 PI assignment sizes, from the standard /48 to larger allocations, and helps you understand how to determine the right size for your requirements.

Understanding IPv6 Prefix Notation

Before diving into PI assignment sizes, let's clarify IPv6 prefix notation.

What Does /48 Mean?

IPv6 addresses are 128 bits long. A prefix length like /48 indicates how many bits are fixed (the network portion), with the remaining bits available for subnetting and host addresses.

A /48 prefix provides:

• 48 bits for the network prefix (fixed)
• 80 bits remaining (flexible)
• 16 bits typically used for subnets (65,536 /64 subnets)
• 64 bits for host addresses in each subnet

IPv6 Subnet Structure

Standard IPv6 addressing hierarchy:

[Global Routing Prefix] [Subnet ID] [Interface ID]
      /48 or shorter       16 bits      64 bits

Example /48 breakdown:

• Network: 2001:db8:1234::/48
• Subnets: 2001:db8:1234:0000::/64 through 2001:db8:1234:ffff::/64
• Total subnets: 65,536 individual /64 networks

Shorter Prefix = More Address Space

In IPv6 notation, a numerically smaller prefix means more address space:

• /48 = 65,536 /64 subnets
• /44 = 1,048,576 /64 subnets (16x more than /48)
• /40 = 16,777,216 /64 subnets (256x more than /48)
• /36 = 268,435,456 /64 subnets (4,096x more than /48)

For comprehensive background on PI resources, see our guide to Understanding Provider Independent (PI) Resources.

Standard IPv6 PI Assignment: /48

The vast majority of organizations receive a /48 as their IPv6 PI assignment.

Policy Definition

RIPE policy clearly states: "The minimum size of the assignment is a /48."

This /48 represents the standard, default IPv6 PI assignment size. Most organizations requesting IPv6 PI space receive exactly this size without needing special justification.

Why /48 is Standard

The /48 size emerged from careful consideration of organizational needs and Internet routing scalability.

Historical context: RFC 3177 originally recommended /48s for organizations and even /48s for home users, though later refined by RFC 6177 which acknowledged more flexible sizing while maintaining /48 as the typical organizational assignment.

Organizational adequacy: A /48 provides 65,536 /64 subnets - far more than most organizations will ever need:

• Small business (1 location): Might use 2-10 subnets
• Medium enterprise (multiple offices): Might use 50-200 subnets
• Large organization (many sites): Might use 1,000-5,000 subnets
• Complex infrastructure: Rarely exceeds 10,000 subnets

Even the largest enterprises typically find 65,536 subnets sufficient.

Routing scalability: While IPv6's address space is enormous, keeping the routing table manageable remains important. Standardizing on /48 as the typical assignment size helps limit routing table growth.

What You Can Do With a /48

A standard /48 IPv6 PI assignment supports:

Geographic distribution:

• Dedicated /64 per physical location
• Multiple subnets per site for network segmentation
• Hundreds or thousands of locations easily accommodated

Network segmentation:

• Separate subnets for different departments
• VLAN-per-subnet architectures
• Security zones and DMZs
• Guest networks and wireless SSIDs

Service infrastructure:

• Point-to-point links (/127 or /126 typically, but carved from /64s)
• Loopback addresses
• Management networks
• Server farms and data centers

Growth headroom:

• Years or decades of expansion
• New sites without renumbering
• Architectural changes without address constraints
• Technology evolution accommodation

/48 Assignment Process

Obtaining a standard /48 IPv6 PI assignment is straightforward:

1. Find a sponsoring LIR (or use RIPE NCC directly if already a member)
2. Prepare basic documentation (legal entity verification, technical description)
3. Submit application through sponsoring LIR
4. RIPE NCC reviews for policy compliance
5. Upon approval, receive /48 assignment

Timeline: Standard /48 assignments typically process within 1-2 weeks with complete documentation.

No special justification: You don't need to justify every subnet or provide detailed utilization plans for a /48. The size is considered standard and appropriate for organizational use.

Larger IPv6 PI Assignments

While /48 suffices for most organizations, some require larger address space.

Policy for Larger Assignments

RIPE policy states: "Assignments larger than a /48 (shorter prefix) or additional assignments exceeding a total of a /48 must be based on address usage or because different routing requirements exist for additional assignments."

Key requirements for larger assignments:

• Documented justification based on address usage OR
• Routing requirements necessitating multiple assignments

Justification Based on Address Usage

Organizations can request shorter prefixes (larger assignments) by documenting subnet requirements.

What constitutes valid justification:

1. Number of /64 subnets needed: Document actual subnet requirements exceeding 65,536 (the capacity of a /48)

2. Network architecture: Detailed topology showing:

   • Number of sites and locations
   • Network segmentation model
   • Subnet allocation scheme
   • Growth projections

3. Infrastructure scale: Evidence of infrastructure requiring exceptional address space:

   • Hundreds or thousands of physical locations
   • Complex segmentation requirements
   • Multiple independent business units
   • Large-scale service provider infrastructure

Example scenarios requiring larger space:

Large multinational enterprise:

• 2,000 office locations globally
• 20 subnets per location average
• Total: 40,000 subnets
• Justification: /48 provides only 65,536 subnets with insufficient headroom
• Appropriate size: /44 (1 million /64 subnets)

Hosting provider:

• 500 customer organizations
• Average 200 subnets per customer
• Total: 100,000 subnets
• Justification: Business model requires extensive subnet allocation
• Appropriate size: /40 or /44

Research network:

• 150 member institutions
• Each institution receives /48 sub-assignment
• Total: Needs to subdivide 150 /48s from assignment
• Justification: Must allocate /48s to member organizations
• Appropriate size: /40 (allows 256 /48 sub-assignments)

Justification Based on Routing Requirements

Organizations can also justify multiple separate /48 assignments (rather than one larger block) based on routing needs.

Valid routing justifications:

1. Geographically distributed sites with independent routing: Organizations with sites requiring different routing policies or upstream providers

2. Organizationally separate units: Divisions or subsidiaries operating independent networks

3. Different service categories: Distinct infrastructure types with different routing requirements

Example:

• Organization operates in 3 continents
• Each region uses different upstream providers
• Different BGP announcements for each region
• Solution: Three separate /48 assignments rather than one /46

Nibble Boundaries

Recent RIPE policy discussions (proposal 2024-02) suggest standardizing PI assignments on nibble boundaries.

What are nibble boundaries?

A nibble represents 4 bits in binary. In IPv6 hexadecimal notation, a nibble corresponds to one hexadecimal digit.

Common nibble boundary prefixes:

• /48 (standard)
• /44 (4,096x the space of /48)
• /40 (65,536x the space of /48)
• /36 (1,048,576x the space of /48)
• /32 (16,777,216x the space of /48)

Why nibble boundaries matter:

• Cleaner hexadecimal representation
• Easier to understand and document
• Simplified routing policies
• Better aggregation potential
• Reduced errors in configuration

Policy proposal considerations: The 2024-02 proposal suggests:

• Standard minimum: /48
• Maximum for PI: /36
• All assignments on nibble boundaries
• Clear progression: /48, /44, /40, /36

While not yet finalized, this indicates likely direction for future policy.

Realistic Size Limits

Practical maximum for PI assignments: While policy doesn't specify a hard maximum, PI assignments rarely exceed /40 and almost never approach /32.

Why limits exist:

1. Routing concerns: Very large PI assignments (like /32) are typically reserved for LIR allocations, not end-user PI assignments

2. Conservation principles: Even with IPv6's vast space, some conservation mindset persists

3. Justification challenges: Demonstrating need for hundreds of millions of /64 subnets is difficult for most organizations

Typical size progression:

• /48: Standard (>95% of assignments)
• /44: Large organizations with substantial infrastructure
• /40: Very large enterprises or special cases
• /36: Extremely rare, exceptional justification required
• /32 or shorter: Not typically assigned as PI space

Multiple IPv6 PI Assignments

Instead of requesting one large assignment, organizations can request multiple separate /48 assignments.

When Multiple Assignments Make Sense

Different routing requirements: Organizations with infrastructure requiring separate BGP announcements:

• Geographically separated networks
• Organizationally distinct entities
• Different service types with distinct routing policies

Administrative separation: Multiple assignments for:

• Separate business units
• Acquired companies maintaining distinct networks
• Different service offerings

Example: A company with operations in Europe, Asia, and North America might request:

• One /48 for European infrastructure
• One /48 for Asian infrastructure
• One /48 for North American infrastructure

Each can be announced separately, enabling geographic traffic engineering.

Multiple Assignment Justification

RIPE policy: "Assignments larger than a /48 (shorter prefix) or additional assignments exceeding a total of a /48 must be based on address usage or because different routing requirements exist for additional assignments."

Documentation needed:

• Explanation of why separate assignments required
• Routing architecture showing different policies
• Network topology for each assignment
• Technical justification for separation

Advantages vs. Single Larger Assignment

Multiple /48s:

• Flexibility in routing announcements
• Clear organizational separation
• Easier to manage distinct networks
• Can return individual assignments if needed

Single larger assignment (like /44):

• Single database entry
• Potential for internal aggregation
• Simpler administrative management
• More address space flexibility within block

Choose based on your routing and organizational structure.

IPv6 PI vs LIR Allocation Sizes

It's important to understand how PI assignment sizes differ from LIR allocations.

LIR Allocations

Minimum LIR allocation: /32

RIPE policy: "LIRs that meet the initial allocation criteria are eligible to receive an initial allocation of /32."

Purpose: LIRs (Local Internet Registries) receive allocations to sub-allocate or assign to their customers. The /32 provides space for hundreds or thousands of customer assignments.

Size progression for LIRs:

• Initial: /32 (default)
• Can request /29 without additional justification
• Larger than /29 requires documentation

PI Assignments vs LIR Allocations

Key differences:

Aspect	IPv6 PI Assignment	LIR Allocation
Standard size	/48	/32
Typical range	/48 to /40	/32 to /29
Purpose	End-user infrastructure	Provider aggregatable space for customers
Sub-assignment	Prohibited	Expected and required
Status in RIPE DB	ASSIGNED PI	ALLOCATED PA

Why the difference?: LIRs need much more space because they're distributing it to many customers. A /32 allows an LIR to assign /48s to 65,536 different customers. End users need only enough space for their own infrastructure.

Becoming an LIR vs Getting PI

Some organizations wonder whether to become an LIR or get PI space.

Choose LIR membership if:

• You provide services to many customers needing addresses
• You want to assign/sub-allocate space to others
• You operate as an ISP or hosting provider
• You need the flexibility of PA space

Choose PI assignment if:

• You need addresses only for your own infrastructure
• Provider independence is important
• You don't want full LIR responsibilities
• Cost efficiency is priority (PI fees lower than LIR membership)

Practical Considerations for Sizing

When determining the right IPv6 PI assignment size, consider:

Current Infrastructure

Inventory your needs:

• Number of physical locations
• Subnets per location (typical: 2-10)
• Data centers and their segmentation
• Special-purpose networks (management, etc.)

Current calculation: Total subnets × 2 (for some redundancy)

Growth Projections

5-year planning horizon: Consider:

• New locations planned
• Infrastructure expansion
• Architectural changes
• Emerging technologies (IoT, containers, etc.)

Buffer for unknown growth: Add 50-100% to projections

Network Architecture

Subnet allocation model:

• Will you allocate /56s or /60s to sites, then subdivide?
• Flat allocation of /64s?
• Hierarchical addressing scheme?

Example hierarchical model:

• /48 PI assignment
• Allocate /56 to each office (allows 256 /64s per site)
• Accommodates 256 offices in this model
• Each office can have hundreds of subnets

Administrative Simplicity

Simpler is often better:

• Most organizations don't need more than /48
• Requesting exact size based on subnet count can seem overly precise
• Standard /48 is faster to approve
• You can request additional /48 later if genuinely needed

Avoid premature optimization: Don't request /44 because you might theoretically need it someday. Start with /48; request additional space if you actually outgrow it.

The Application Process for Different Sizes

The process varies slightly depending on assignment size.

Standard /48 Application

Documentation needed:

• Legal entity verification
• Basic technical description
• General network information
• Sponsoring LIR agreement

Justification: Minimal - /48 is considered appropriate for organizational use

Approval time: 1-2 weeks typically

Larger Assignment Application

Additional documentation required:

• Detailed network topology
• Subnet allocation plan
• Infrastructure inventory
• Growth projections with timelines
• Specific justification for size needed

Justification depth: Must clearly demonstrate why /48 is insufficient

Approval time: 2-4 weeks typically, may require clarifications

RIPE NCC evaluation: Scrutiny increases with assignment size. Be prepared to:

• Answer detailed questions
• Provide additional documentation
• Justify specific subnet requirements
• Explain architecture choices

Common Sizing Mistakes

Over-requesting

Mistake: Requesting /40 or /44 "just in case" without genuine justification.

Problem:

• Slows approval process
• May result in rejection or downsizing
• Wastes time with additional documentation

Solution: Start with /48 unless you have clear, documented need for more.

Under-estimating

Mistake: Accepting /48 when your documented infrastructure genuinely exceeds 65,000 subnets.

Problem:

• May need to request additional space later
• Could require architectural workarounds
• Complicates addressing scheme

Solution: Honestly assess your subnet requirements and request appropriate size if /48 truly insufficient.

Confusing with IPv4 Thinking

Mistake: Applying IPv4 scarcity mindset to IPv6.

Problem:

• Requesting large space thinking it's scarce (it's not)
• Or being overly conservative with IPv6 (unnecessary)

Solution: /48 is generous by design. For most organizations, it's perfect.

Ignoring Routing Reality

Mistake: Requesting multiple /48s without routing justification, or requesting /36 when /44 would suffice.

Problem:

• RIPE NCC may question or reject
• Routing table implications
• Unnecessary complexity

Solution: Align assignment size with genuine routing and architectural requirements.

Summary: IPv6 PI Assignment Sizes

Standard assignment: /48 (65,536 /64 subnets)

• Appropriate for >95% of organizations
• No special justification needed
• Fast approval process

Larger assignments: /44, /40, /36 possible

• Requires documented justification
• Based on subnet count or routing needs
• Longer approval process

Multiple assignments: Separate /48s for distinct infrastructure

• Justified by routing requirements
• Organizational or geographic separation
• Different from single large assignment

Size philosophy: IPv6 PI policy is generous

• /48 is ample for most organizations
• Request larger only when genuinely needed
• Focus on routing architecture, not artificial scarcity

Key policy: "The minimum size of the assignment is a /48. Assignments larger than a /48 (shorter prefix) or additional assignments exceeding a total of a /48 must be based on address usage or because different routing requirements exist for additional assignments."

Frequently Asked Questions

Is /48 really enough for a large organization?

For most large organizations, yes. A /48 provides 65,536 /64 subnets. Even an organization with 500 locations using 50 subnets per location needs only 25,000 subnets. If you genuinely need more, document it and request a /44 or /40.

Can I request a /32 as PI space?

Highly unlikely. /32 allocations are typically reserved for LIRs, not end-user PI assignments. If you believe you need /32-scale space, consider becoming an LIR instead.

What if I outgrow my /48?

You can request an additional /48 assignment or request an upgrade to larger space. Document your growth and subnet usage, and work with your sponsoring LIR to submit the request.

Should I request multiple /48s or one /44?

Depends on your routing needs. If you have distinct networks with different routing policies (geographic regions, separate business units, etc.), multiple /48s make sense. If you just need more space within one routing domain, a single /44 is cleaner.

How do I justify needing more than /48?

Document your subnet requirements clearly: number of sites, subnets per site, segmentation model, growth plans. Provide network topology diagrams. Explain why 65,536 /64 subnets are insufficient for your infrastructure.

Can I subnet my /48 into /56s for different locations?

Absolutely. This is common practice. A /48 contains 256 /56s, each of which contains 256 /64s. You might allocate /56 per office location, giving each office 256 subnets to work with.

Are there ongoing fees based on assignment size?

No. RIPE NCC charges the same annual fee (€75 as of 2025) regardless of whether you have a /48 or /40. Size doesn't impact maintenance fees.

What's the largest PI assignment RIPE will approve?

While policy doesn't specify a hard maximum, PI assignments rarely exceed /40 and almost never reach /36. Anything shorter than /40 requires exceptional justification.

Next Steps

Ready to request your IPv6 PI assignment?

Assess your requirements:

• Inventory current subnet needs
• Project 5-year growth
• Evaluate network architecture
• Determine if /48 is sufficient (it probably is)

Prepare documentation:

• Network topology diagrams
• Subnet allocation plan (if requesting larger than /48)
• Legal entity verification
• Technical descriptions

Find a sponsoring LIR: Partner with an experienced provider like Via-Registry who can guide you through the process.

Submit your application: Work with your sponsoring LIR to submit to RIPE NCC.

Via-Registry simplifies IPv6 PI assignments:

• Standard /48 assignments: €200-400 total annual cost
• Larger assignments: Expert justification assistance
• Complete application support
• Ongoing management services

Learn more about our IPv6 PI Resources Service.

Related resources:

• Understanding Provider Independent (PI) Resources
• Documentation Needed for PI Requests
• RIPE PI Resource Application Process

Contact Via-Registry to discuss your IPv6 PI assignment needs.

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This article is part of our comprehensive resource library on IP addressing and Internet resources. For personalized guidance on IPv6 PI sizing, contact our team or explore our service offerings.