IPv6 PI Allocation Sizes Explained

The RIPE NCC assigns IPv6 PI space as a /48 by default. Section 7.1 of the IPv6 policy (ripe-738) makes a /48 the minimum, and a larger block, or a second assignment, must be justified by address usage or by different routing requirements (section 5.4.2). A /48 holds 65,536 /64 subnets, and 4,127 of the 4,191 IPv6 assignment records in the RIPE NCC delegated statistics of 24 September 2026 are /48s.

Understanding 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)

Standard IPv6 PI Assignment: /48

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

Policy Definition

The IPv6 Address Allocation and Assignment Policy (ripe-738) states in section 7.1: "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

Historical context: RFC 3177 (2001) recommended a /48 for almost every end site, homes included. RFC 6177 (BCP 157, 2011) obsoleted it: a single /48 default is no longer recommended, and the size is left to operators and registries. For PI, the RIPE community kept /48 as the minimum (ripe-738 section 7.1).

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

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

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

Filtering: ripe-738 section 7 assigns PI "from a separate 'designated block' to facilitate filtering practices", so operators can tell PI /48s from more-specifics of PA allocations and set their prefix filters accordingly.

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

Cloud BYOIP:

• AWS accepts a /48 as the most specific advertisable IPv6 range (a /60 if not advertised), and Azure needs a /48 as the global parent prefix; BYOIP explained covers the steps

Growth headroom:

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

/48 Assignment Process

Steps for a /48:

1. Find a sponsoring LIR (or use RIPE NCC directly if already a member)
2. Prepare the documents: an identity document for a natural person, or registration papers for a company, checked under ripe-863, plus a signed End User agreement with the sponsoring LIR (ripe-637); see Documentation Needed for PI Requests
3. Submit application through sponsoring LIR
4. RIPE NCC reviews for policy compliance
5. Upon approval, receive /48 assignment

IPv6 PI has no multihoming requirement: ripe-738 section 7 contains no such clause.

Timeline: The RIPE NCC publishes no processing time for IPv6 PI requests. A larger request draws more questions, so expect more back and forth.

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
   • Several business units of the same legal entity
   • Large-scale service provider infrastructure

Example scenarios:

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: PI covers the provider's own infrastructure. Servers in its racks can take individual addresses from its subnets (ripe-738 section 2.6), and an LIR can hold PI for infrastructure it does not use for customer end sites (section 7.2). Handing a /64 or a /56 to each customer organization is a sub-assignment, which section 7 forbids for PI. A provider that routes prefixes to customers needs PA space: an allocation of its own as an LIR, or a block leased from an LIR's allocation. PI vs PA resources compares the two.

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 of the same organization running separately routed networks. A subsidiary that is its own legal entity needs its own PI assignment, because PI cannot be sub-assigned to another organization (ripe-738 section 7)
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

Proposal 2024-01 (Revised IPv6 PI Assignment Policy) would issue justified PI assignments on nibble boundaries. Version 3.0 was published on 25 August 2026, and its Review Phase ran from 25 August to 23 September 2026. The Address Policy Working Group chairs had not announced a decision on 25 September 2026, so ripe-738 still sets the sizes.

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 (16 /48s)
• /40 (256 /48s)
• /36 (4,096 /48s)
• /32 (65,536 /48s)

The proposal's stated aim is "to aid aggregation and reduce the need for renumbering in case of growth" (2024-01, section 7.1.1). A block that grows from /48 to /44 keeps its first hexadecimal digits, so nothing already deployed has to move.

Version 3.0 of the proposal would set the minimum at /48, issue larger blocks in steps of four bits (/48, /44, /40, /36), cap PI at a /36 (one step more specific than the smallest allocation) and register each holder's assignment in a single object. Need would be justified over the next 24 months, and an End User who documents a need for two /48s would receive a /44. It is a proposal, not policy: until the chairs declare consensus and the RIPE NCC implements it, a larger PI block follows ripe-738 section 5.4.2.

Realistic Size Limits

Practical maximum for PI assignments: ripe-738 sets no maximum PI size. In the RIPE NCC delegated statistics of 24 September 2026, 57 IPv6 assignment records are /45 to /47 and 7 are /44 or shorter, out of 4,191. The file does not separate PI from anycast and IXP assignments, so the largest records are not necessarily PI. Proposal 2024-01 would cap PI at a /36.

Size distribution (RIPE NCC delegated statistics, 24 September 2026):

• /48: 4,127 records (98.5%)
• /47 to /45: 57 records
• /44 or shorter: 7 records

Multiple IPv6 PI Assignments

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

When Multiple Assignments Make Sense

Separate /48s fit infrastructure that needs separate BGP announcements: regions with different upstream providers, or divisions of one organization with distinct routing policies. According to the RIPE NCC's impact analysis of proposal 2024-01, requests for additional IPv6 PI space are "negligible" in number today, so expect the RIPE NCC to ask why one block will not do.

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

The same rule applies: ripe-738 section 5.4.2 requires address usage or different routing requirements for additional assignments beyond a /48 in total.

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
• Each /48 can be transferred or returned on its own; a single /48 cannot be split for a transfer, since the RIPE NCC's minimum transfer size for IPv6 PI is a /48

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-738 sets the minimum allocation at a /32 (section 4.3). An LIR that meets the initial criteria can receive "an initial allocation of /32 up to /29 without needing to supply any additional information" (section 5.1.2).

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:

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

LIR vs PI compares membership with a sponsored PI block in detail.

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: €75 per PI assignment per year at the RIPE NCC, against €1,800 per year plus €1,000 to join as a member under the Charging Scheme 2026 (ripe-848); in 2027 the membership fee is €1,894 with one ASN included (ripe-867)

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 (typically 2 to 10)
• Data centers and their segmentation
• Special-purpose networks (management, etc.)

Growth Projections

Planning horizon: Proposal 2024-01 would have need justified over the next 24 months, a sensible horizon under current policy too. Consider:

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

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

The IPv6 subnet calculator shows the /56 and /64 counts for any split.

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
• 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: the identity or registration papers and the signed End User agreement listed above, plus a short description of the network. No subnet-by-subnet plan: a /48 needs no size justification.

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

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:

• Draws more questions from the RIPE NCC
• 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 a /48 when your documented infrastructure needs more than 65,536 subnets within 24 months.

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: A /48 holds 65,536 /64s. Start there.

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

A RIPE PI assignment starts at a /48, and 98.5% of the RIPE NCC's IPv6 assignment records were exactly that size on 24 September 2026. More space, or a second /48, needs documented usage or a separate routing requirement under ripe-738 section 5.4.2. Space for customers is a sub-assignment and belongs in PA, not PI.

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.

What if I outgrow my /48?

Request an additional assignment through your sponsoring LIR. Under ripe-738 section 5.4.2 it must rest on documented address usage or a different routing requirement. The RIPE NCC cannot extend an existing PI block today: its impact analysis of proposal 2024-01 lists extension as software still to be built, and notes that the /46 it currently reserves behind a /48 would not cover an extension to /44. Extensions to the next nibble boundary are part of the proposal, which is not policy.

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?

Show why 65,536 /64 subnets are not enough: sites, subnets per site, the segmentation model and the growth expected over the next 24 months, with a topology diagram. The section on justification based on address usage above lists what the RIPE NCC looks at.

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

Yes. A /48 contains 256 /56s of 256 /64s each, so one /56 per site covers 256 sites with 256 subnets each.

Are there ongoing fees based on assignment size?

No. The RIPE NCC charges €75 per independent assignment per year under the Charging Scheme 2026 (ripe-848) whether the block is a /48 or a /40, and the fee stays €75 in 2027 under ripe-867, adopted at the May 2026 General Meeting.

What's the largest PI assignment RIPE will approve?

ripe-738 sets no maximum, and the RIPE NCC delegated statistics of 24 September 2026 show 7 IPv6 assignment records at /44 or shorter out of 4,191. A /32 is an allocation size, the minimum an LIR receives, and comes with RIPE NCC membership rather than as PI. Proposal 2024-01 would cap PI at a /36.

Next Steps

We file IPv6 PI /48 applications as your sponsoring LIR: €300 setup plus €135 per year, so €435 the first year (as of September 2026). The €135 includes the RIPE NCC's €75 assignment fee at cost. The block is registered to your organization and stays with you if you change sponsoring LIR, and you sign its ROAs in your own End User hosted CA at the RIPE NCC. If you already hold a PI block and your LIR is closing, or you want to leave it, change your sponsoring LIR covers the ten-working-day window.

Related reading:

• Understanding Provider Independent (PI) Resources
• RIPE PI Resource Application Process

Contact us about an IPv6 PI assignment.