The document discusses IPv6 address planning and subnetting. It explains that creating an IPv6 address plan helps with routing, security policies, network management and troubleshooting. Unlike IPv4, the focus for IPv6 subnetting is on network planning and optimization rather than conserving addresses. The document provides examples of how to plan and assign subnets using different factors like location, business units, applications and regions. It also discusses calculating the number of required subnets and choosing a subnet prefix length.

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IPv6 Address Planning
Dan York
Deploy360 Programme
www.internetsociety.org/deploy360/

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Objectives
After this section, you should be able to:
• Understand the value of an IPv6 address plan
• Plan how you will assign IPv6 subnets
• Estimate the IPv6 addressing needs of your network
• Subnet an IPv6 prefix

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Why Create An IPv6 Address Plan?
• Routing tables can be smaller and more efficient
• Security policies can be easier to implement
• Application policies can be implemented
• Network management/provisioning can be easier
• Troubleshooting can be easier, particularly with visual
identification
• Easier scaling as more devices or locations are added

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IPv4 Subnetting Concepts To Forget!
Why do we do subnetting?
• IPv4: Conserve address space
• IPv6: planning and optimization for routing and security
Subnets vs hosts – number of hosts irrelevant in IPv6
• There will rarely be a need to expand a /64 subnet (264 hosts)
• 264 = 18,446,744,073,709,551,616 hosts

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IPv6 Address Planning Basics
9/25/13

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A Typical IPv6 Address For A Device (Host)
2001:db8:1234:152c:12b4:5678:d334:9af
Host (/64)
Prefix (/64)

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Network Prefixes
2001:db8:1234:152c:12b4:5678:d334:9af
Host (/64)
/16
/32
/48

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Address Block Assignments
9/23/13
Prefix Assignment Number of Addresses
/32 LIR (Local Internet Registry) – often an ISP 296
/48 Organization 280
/64 Organization network 264
/128 Individual host (PC, server, router, etc.) 1

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/32 Prefix
2001:db8:1234:152c:12b4:5678:d334:9af
Host (/64)
Prefix (/32) Subnet (/32)

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/48 Prefix
2001:db8:1234:152c:12b4:5678:d334:9af
Host (/64)
Prefix (/48) Subnet (/16)

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Common Prefixes - /48, /52, /56, /60
2001:db8:1234:152c:12b4:5678:d334:9af
Prefix (/48) Subnet (/16)
2001:db8:1234:152c:12b4:5678:d334:9af
Prefix (/52) Subnet (/12)
2001:db8:1234:152c:12b4:5678:d334:9af
Prefix (/56) Subnet (/8)
2001:db8:1234:152c:12b4:5678:d334:9af
Prefix (/60) Subnet (/4)

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Common Subnet Prefixes
9/23/13
Prefix Number of /64 Subnets
/48 65,536
/52 4,096
/56 256
/60 16
/64 1

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Common Subnet Prefixes - # of Subnets
9/23/13
Prefix /52
Subnets
/56
Subnets
/60
Subnets
/64
Subnets
/48 16 256 4,096 65,536
/52 16 256 4,096
/56 16 256
/60 16
/64 1
Ex. a /52 prefix could have:
• 16 /56 subnets
• 256 /60 subnets
• 4,096 /64 subnets

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Example Allocation
9/24/13
Core
Region 1
Site 1 Site 2
Region 2
Site 3 Site 4 Site 5
Region 3
Site 6 Site 7
Internet
LANLANLANLAN LAN LAN LAN
/48
/52
/64/64 /64 /64 /64 /64 /64
/52 /52

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Using "Nibbles" as boundaries
• A "nibble" is one hexadecimal digit (or 4 bits)
• You don't have to subnet based on nibbles. You can
use other prefixes, ex. /49, /51, /54
• But it is MUCH easier to identify addresses if you do.
hex 1234
binary 0001:0010:0011:0100

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Example: Very Simple Subnets
2001:db8:1234:1000::/64
Prefix (/48) Subnet (/16)
2001:db8:1234:2000::/64
2001:db8:1234:3000::/64
2001:db8:1234:4000::/64
2001:db8:1234:f000::/64
…

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Example: Very Simple Subnets
2001:db8:1234:1::/64
Prefix (/48) Subnet (/16)
2001:db8:1234:2::/64
2001:db8:1234:3::/64
2001:db8:1234:4::/64
2001:db8:1234:f::/64
…

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Key Point: Focus on the 16 bits (and 4 nibbles)
2001:db8:1234:152c:12b4:5678:d334:9af
Host (/64)
Prefix (/48) Subnet (/16)

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Subnet Planning
9/25/13

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Next Step: Plan Your Subnet Scheme
• Multiple ways to use the 4 nibbles (assuming a /48)
• Plan nibbles by:
• Region and site
• Location
• Use type (ex. employees, students, guests)
• Business units
• Applications (ex. data, voice, video)
• Combinations of some of the above
• THERE IS NO ONE RIGHT ANSWER!
• Will depend upon your site and your objectives
9/24/13

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Example Planning Considerations
• Do you want to optimize for your security policies?
• Do you want to make it easy for firewalls to filter based on… location?
user type? applications?
• Do you want to optimize for router policies and
performance?
• Do you want to have the smallest and most efficient routing table
possible?
• Do you have a higher or lower quantity of certain
types of objects?
• For example, do you only have 2 locations but 20 types of applications?

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Example #1: Location and Use Type
2001:db8:1234:152c:12b4:5678:d334:9af
Prefix (/48) Subnet (/16)
Location (16):
• Building 1
• Building 2
• Building 3
Use Type (16):
• Employees
• Servers
• Infrastructure
Individual
networks (256)

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Example #2: Locations (many) and Use Type
2001:db8:1234:152c:12b4:5678:d334:9af
Prefix (/48) Subnet (/16)
Location (256):
• Building 1
• Building 2
• Building 3
Use Type (16):
• Employees
• Servers
• Infrastructure
Individual
networks (16)

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Example #3 – business units first
Start by allocating based on business units:
• Corporate: 2001:db8:1a:0000::/52
• Finance: 2001:db8:1a:1000::/52
• Marketing: 2001:db8:1a:2000::/52
• Engineering: 2001:db8:1a:3000::/52
• Customer Support: 2001:db8:1a:4000::/52
Then allocate on applications (here for one unit):
• Engineering - Data: 2001:db8:1a:3000::/56
• Engineering - Voice: 2001:db8:1a:3200::/56
• Engineering - Video: 2001:db8:1a:3400::/56
• Engineering - Wireless: 2001:db8:1a:3800::/56
• Engineering - Management:2001:db8:1a:3c00::/56
9/24/13

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Example #3, continued
Next allocate based on region (here for "Data"):
• Engineering - Data – Eastern region: 2001:db8:1a:3000::/60
• Engineering - Data – Northern region: 2001:db8:1a:3080::/60
• Engineering - Data – Western region: 2001:db8:1a:3040::/60
• Engineering - Data – Southern region: 2001:db8:1a:30c0::/60
Then allocate on individual sites:
• Engineering - Data - Northern region - Site 0: 2001:db8:1a:3080::/64
• Engineering - Data - Northern region - Site 1: 2001:db8:1a:3081::/64
• Engineering - Data - Northern region - Site 2: 2001:db8:1a:3082::/64
9/24/13

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Example #4 – applications first
Start by allocating based on applications:
• Data: 2001:db8:1a:0000::/52
• Voice: 2001:db8:1a:8000::/52
• Video: 2001:db8:1a:4000::/52
• Wireless: 2001:db8:1a:c000::/52
• Management: 2001:db8:1a:2000::/52
Then allocate on regions (here for one unit):
• Voice – Eastern region: 2001:db8:1a:8000::/56
• Voice – Northern region: 2001:db8:1a:8800::/56
• Voice – Western region: 2001:db8:1a:8400::/56
• Voice – Southern region: 2001:db8:1a:8c00::/56
9/24/13

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Example #4, continued
Next allocate based on business unit:
• Voice – Southern region – Corporate: 2001:db8:1a:8c00::/60
• Voice – Southern region – Finance: 2001:db8:1a:8c10::/60
• Voice – Southern region – Marketing: 2001:db8:1a:8c20::/60
• Voice – Southern region – Engineering: 2001:db8:1a:8c30::/60
• Voice – Southern region – Cust Support: 2001:db8:1a:8c40::/60
Then finally on individual sites:
• Voice – Southern– Marketing – Site 1: 2001:db8:1a:8c2a::/64
• Voice – Southern– Marketing – Site 2: 2001:db8:1a:8c29::/64
• Voice – Southern– Marketing – Site 3: 2001:db8:1a:8c2e::/64
9/24/13

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Again: focus on the 16 bits (and 4 nibbles)
2001:db8:1234:152c:12b4:5678:d334:9af
Host (/64)
Prefix (/48) Subnet (/16)

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Subnet Numbering: Planning For Growth
Multiple ways for numbering individual subnets:
• Numerical (monotonic) – just increment by 1:
• 2001:db8:1234:0000::/64
• 2001:db8:1234:1000::/64
• 2001:db3:1234:2000::/64
• Sparse allocation (RFC 3531)
• 2001:db8:1234:0000::/64
• 2001:db8:1234:8000::/64
• 2001:db3:1234:4000::/64
• Random allocation
• Randomly choose numbers
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Calculating The # Of Required Subnets
• Determine primary factor you want to use
• Ex. location
• Determine number of needed groups
• Ex. 15 locations, 2 administrative groups, 5 future = 22 total
• Round up to nearest nibble
• Ex. 22 would fit within 2 nibbles (256 values)
• Decide what to do with remaining nibbles (if any)
• Continue subnetting with a secondary factor
• Don't subdivide and just have large subnets
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How Many Nibbles?
9/24/13
# of nibbles Number of subnets
1 16
2 256
3 4,096
4 65,536
2001:db8:1234:152c:12b4:5678:d334:9af

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Other Subnet Schemes
• VLAN Numbers
• Organization may already have location/type planned into VLANs
• Mirroring IPv4 Networks
• Point-to-point / inter-router links
• RFC 6164 suggests use of /127 prefixes
• You may want to reserve a /64 and then assign a /127
9/24/13

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Subnetting on non-nibble boundaries
• Again, you can subnet on non-nibble boundaries
• Can make more efficient use of space, just may be harder to use
• Calculate # of bits necessary by finding the nearest
power of 2 greater than or equal to value
• If 6 locations, 8 (23) is closest so 3 bits would be needed.
• If 20 locations, 32 (25) is closest so 5 bits would be needed.
• Example of subnet boundaries using 3 bits (/51):
• Subnet 1 – 2001:db8:1a:0::/51
• Values – 2001:db8:1a:0:0:0:0:0 – 2001:db8:1a:1fff:ffff:ffff:ffff:ffff
• Subnet 2 – 2001:db8:1a:2000::/51
• Values – 2001:db8:1a:2000:0:0:0:0 – 2001:db8:1a:3fff:ffff:ffff:ffff:ffff
• Subnet 3 – 2001:db8:1a:4000::/51
9/24/13

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Subnets at an Internet Service Provider (ISP) or
Local Internet Registry (LIR)
9/25/13

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ISP/LIR Customers Typically Receive A /48
Prefix
2001:db8:1234:152c:12b4:5678:d334:9af
Host (/64)
Prefix (/48) Subnet (/16)

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ISPs/LIRs Typically Receive A /32 Prefix
2001:db8:1234:152c:12b4:5678:d334:9af
Host (/64)
Prefix (/32) Subnet (/32)

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Allocating a /32 at the LIR Level
2001:db8:1234:152c:12b4:5678:d334:9af
Host (/64)
Prefix (/32) Subnet (/16)
Subnet (/16)
Prefix (/48)

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Again a focus on 16 bits (4 nibbles)
2001:db8:1234:152c:12b4:5678:d334:9af
Host (/64)
Prefix (/32) Subnet (/16)
Subnet (/16)
Prefix (/48)

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Using Nibbles: # of /48 Subnets In a /32
9/23/13
Prefix /36
Subnets
/40
Subnets
/44
Subnets
/48
Subnets
/32 16 256 4,096 65,536
/36 16 256 4,096
/40 16 256
/44 16
/48 1
2001:db8:1234:152c:12b4:5678:d334:9af
2001:db8::/32
2001:db8:1000:/36
2001:db8:1200:/40
2001:db8:1230:/44
2001:db8:1234:/48

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Subnetting At A Bit Level
2001:db8:1234:152c:12b4:5678:d334:9af
0001001000110100

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Bits And Subnets
• Helpful to think of number of possible subnets for
each bit used:
• Using 1 bit gets you 2 subnets, 2 bits gets you 4 …
• May be more helpful to view it in this form:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16384 32768 65536
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
65536 32768 16384 8192 4096 2048 1024 512 256 128 64 32 16 8 4 2

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Subnetting At A Bit Level
• If you use __ bits, you will have __ subnets and use a __ prefix
• Ex: 2001:db8:1230::/44 – 16 subnets - entire last nibble
2001:db8:1230::/47 – 2 subnets
• 2001:db8:1230:: - 2001:db8:1237::
• 2001:db8:1238:: - 2001:db8:123f::
2001:db8:1234:152c:12b4:5678:d334:9af
0001001000110100
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
65536 32768 16384 8192 4096 2048 1024 512 256 128 64 32 16 8 4 2 1
/32 /33 /34 /35 /36 /37 /38 /39 /40 /41 /42 /43 /44 /45 /46 /47 /48
Prefix (/32)
Subnet (/16)

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Assigning Individual Subnets
• 2001:db8:1230::/44 – 16 subnets – entire nibble (increment by 1)
• 2001:db8:1230::/47 – 2 subnets
• 2001:db8:1230::/47 - 2001:db8:1230:: - 2001:db8:1237::
• 2001:db8:1238::/47 - 2001:db8:1238:: - 2001:db8:123f::
• 2001:db8:1230::/46 – 4 subnets
• 2001:db8:1230::/46 - 2001:db8:1230:: - 2001:db8:1233::
• 2001:db8:1234::/46 - 2001:db8:1234:: - 2001:db8:1237::
• 2001:db8:1238::/46 - 2001:db8:1238:: - 2001:db8:123b::
• 2001:db8:123c::/46 - 2001:db8:123c:: - 2001:db8:123f::
2001:db8:1234:152c:12b4:5678:d334:9af
Bits 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Subnets 65536 32768 16384 8192 4096 2048 1024 512 256 128 64 32 16 8 4 2
Prefix /32 /33 /34 /35 /36 /37 /38 /39 /40 /41 /42 /43 /44 /45 /46 /47
Nibble
Hex
Increment
1 2 4 8 1 2 4 8 1 2 4 8 1 2 4 8
Prefix (/32)
Subnet (/16)

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Requesting IPv6 Addresses
• Many ISPs/LIRs simply request a /32
• 2001:db8::/32
• You can request larger address space
• How many /32s do you want to have?
• See:
• http://www.internetsociety.org/deploy360/resources/how-to-get-ipv6-addresses/

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Requesting Greater Than A /32
• If you use __ bits, you will have __ subnets and use a __ prefix
• If you want 2 /32's, request a /31
• RIRs may have different policies about what size
address blocks you can obtain
2001:0db8:1234:152c:12b4:5678:d334:9af
0000110110111000
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
65536 32768 16384 8192 4096 2048 1024 512 256 128 64 32 16 8 4 2 1
/16 /17 /18 /19 /20 /21 /22 /23 /24 /25 /26 /27 /28 /29 /30 /31 /32

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Recommendations and Resources
9/25/13

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Closing Recommendations
• Ensure that all prefixes fall on nibble boundaries
• Plan a hierarchical scheme for easy aggregation or
enforcement of policies
• Allocate /64 prefixes for all end subnets
• Consider scalability and future potential growth
• Think about how well your plan might handle
renumbering
• Document your planning thoroughly

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Resources
AFRINIC IPv6 Foundations
• http://learn.afrinic.net/index.php/en/resources/ipv6
SURFnet / RIPE NCC "Preparing an IPv6 Address Plan"
• http://www.surfnet.nl/Documents/rapport_201309_IPv6_numplan_EN.pdf
Internet Society Deploy360 Programme
• http://www.internetsociety.org/deploy360/ipv6/basics/
• http://www.internetsociety.org/deploy360/resources/ipv6-address-planning/
9/25/13

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york@isoc.org
http://www.internetsociety.org/deploy360/
Dan York
Senior Content Strategist
Internet Society
Thank You!