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

2. www.internetsociety.org/deploy360/
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
9/24/13

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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
9/24/13

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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!