PREPARING AN
IPV6 ADDRESS PLAN
MANUALPREPARING AN IPV6 ADDRESS PLAN
MANUAL

Version 2, 18 September 2013

CONTENTS
1. Introduction	......................................................................................................................................................3
1.1.

For Whom is this Document Intended? ...........................................................................3

2. Structure of IPv6 Addresses	...................................................................................................................3
2.1.
2.2.
2.3.
2.4.
2.5.

Address Notation ............................................................................................................3
Prefixes: Grouping Addresses ........................................................................................4/64 Subnets .....................................................................................................................6
Assigning Address Blocks ..............................................................................................6
Representation of Subdivisions .......................................................................................7

3. Options Without an Address Plan	

......................................................................................................7
3.1.
3.2.

Direct Link Between IPv4 and IPv6 Subnets ...................................................................8
Direct Link Between IPv4 and IPv6 Addresses ...............................................................8

4. Preparing an Address Plan	

.......................................................................................................................9
4.1.
4.2.
4.3.

4.4.

Basic Structure of the Address Plan ...............................................................................9
IPv6, NAT and Firewalls.................................................................................................10
Router vs Firewall: Location or Use Type First ..............................................................10

4.3.1.

Location First	.....................................................................................................................................................10

4.3.2.

Use Type First	....................................................................................................................................................10

4.3.3.

Recommendation	...........................................................................................................................................10

Determining the Address Space Required for the Address Plan .................................10

4.4.1.

Example 1: Location-based subnet	

.......................................................................................................11

4.4.2.

Example 2: Use type-based subnet	

......................................................................................................124.5. Optional Secondary Subnets ........................................................................................13
4.6. Double Check ...............................................................................................................13
4.7. Leeway ..........................................................................................................................13
4.8. Legibility ........................................................................................................................144.9. Flexibility for Future Growth ...........................................................................................15
4.10. Using VLAN Numbers ...................................................................................................15
4.11. VLAN Numbers That Encode Location/Use Type .........................................................16

4.11.1. Reversing VLAN Notation in an IPv6 Structure	...........................................................................17
4.11.2. Hexadecimal Notation	................................................................................................................................17
4.11.3. Decimal Notation	...........................................................................................................................................174.12. Addressing Point-to-point Links ....................................................................................18
4.13. EUI-64 Addressing ........................................................................................................18

5. Managing and Addressing Hosts	........................................................................................................19
5.1.
5.2.
5.3.
5.4.
5.5.
5.6.

Stateless Address Autoconfiguration ............................................................................19
Privacy Addresses ........................................................................................................19
Dynamic Host Configuration Protocol for IPv6 (DHCPv6) .............................................20
Manual Address Configuration .....................................................................................20
Router Advertisement Guard ........................................................................................20
DNS Considerations ......................................................................................................21

Acknowledgements	..................................................................................................................................22
Appendix: Detailed Examples	.............................................................................................................232	

	

Preparing an IPv6 Address Plan1.

INTRODUCTION

IPv4 addresses have almost run out, and more and more businesses and institutions see thenecessity to migrate to IPv6. As a result, they need an IPv6 address plan. An IPv6 address is 128
bits long, which means that, in theory, there are 2128 addresses available, a great deal more thanthe 232 (= 4.3 billion) addresses available with IPv4. To give you an idea of the volume: 2128 or
340 282 366 920 938 463 463 374 607 431 768 211 456 or 340 billion billion billion billion
represents approximately the number of grains of sand on our planet. This means that an IPv6
address plan will look very different from an IPv4 address plan.
An address plan using the IPv4 system limits the options available to an organisation because
there are relatively few IPv4 addresses still available. This is why the IPv4 addressing system isbased on efficient address assignment. If you apply for an IPv6 address range at many Internet
Service Providers, you will be assigned 280 addresses (a /48 prefix). This is such a huge amountthat efficiency virtually ceases to be an issue. This is why it is worthwhile adopting an IPv6
address plan: a system in which you assign the IPv6 addresses to locations and/or use types.
In an efficient IPv6 address plan, the IPv6 addressing ranges are grouped effectively and logically.
This has several advantages, including:
•

•

•

•

Security policies are easier to implement, such as the configuration of access lists andfirewalls
Addresses are easier to trace: the address contains information about the use type or
location where the address is in use
An efficient address plan is scalable: it can be expanded, for example, to include newlocations or use types
An efficient IPv6 address plan also enables more efficient network management

However, an efficient IPv6 address plan may "waste" large numbers of IPv6 addresses. In almost
all cases, this is a good trade-off: seemingly wasteful practices lead to more efficiency elsewhere,
for instance, by avoiding unnecessary inflation of routing tables in routers. The addresses are
there; you may as well use them.
This manual will show you how to prepare an effective IPv6 address plan. In making that plan,
you will need to make a number of important choices. Please think carefully about these choices
to ensure that the address plan will meet the requirements of your organisation. This manual will
provide suggestions to help you to make the right choices.
1.1.

For Whom is this Document Intended?

This manual is intended for network architects and network managers implementing IPv6 intheir organisations. We assume you have experience in setting up IPv4 networks.

2.

STRUCTURE OF IPV6 ADDRESSES

IPv6 addresses are 128 bits long, four times as long as IPv4 addresses. As a result, they're written
down differently, and the large number of bits to work with allows for more internal structure
within the IPv6 address.
2.1.

Address Notation

An IPv6 address consists of 128 bits that can each have a value of 0 or 1. Because an address
made up of 128 ones and zeroes is illegible, a more convenient format has been devised. This
3	

	Preparing an IPv6 Address Plan

format is based on the hexadecimal system1 , which is much easier to understand for humans
while being closely related to the binary format.
Each digit in the hexadecimal system is equivalent to 4 bits; an IPv6 address of 128 bits
therefore consists of 128 / 4 = 32 hexadecimal digits. The notation is as follows:
2001:0db8:0000:0000:0000:0000:0000:0001

Since it is impractical to record all these zeroes, some may be skipped in accordance withcertain conventions. Leading zeroes can be dropped for each group of digits. The result would
then be:2001:db8:0:0:0:0:0:1
One (and only one) series of zeroes and colons may also be abbreviated as two colons. The
result is now:
2001:db8::1
The precise rules for IPv6 address notation are specified in RFC 59522.
2.2.

Prefixes: Grouping Addresses

IPv6 addresses are grouped using the binary value of the address. This grouping is carried out
using a “prefix”. Prefixes are all addresses that start with the same series of bits, similar to anarea code for phone numbers (e.g., the prefix for Amsterdam is 020). The length of the identicalseries is noted after the address, separated by a forward slash. The prefix
2001:db8::/32
thus contains all the addresses from2001:0db8:0000:0000:0000:0000:0000:0000
through
2001:0db8:ﬀﬀ:ﬀﬀ:ﬀﬀ:ﬀﬀ:ﬀﬀ:ﬀﬀ
As can be seen above, the first 32 bits, i.e. the first eight hexadecimal digits, are identical. The
prefix2001:db8:1234::/64
contains all the addresses from1 http://betterexplained.com/articles/numbers-and-bases/
2 http://tools.ietf.org/html/rfc5952#page-104		Preparing an IPv6 Address Plan

2001:0db8:1234:0000:0000:0000:0000:0000
through
2001:0db8:1234:0000:ﬀﬀ:ﬀﬀ:ﬀﬀ:ﬀﬀ(Don't be fooled by the missing zeroes in 2001:db8:1234::/64 rather than
2001:db8:1234:0000::/64.)
Prefixes that are multiples of four bits are easiest to work with, so those are common. Examples
are /32, /48, /52, /56, /60 and /64. If a prefix falls on a different boundary, this means it "slices"
through a a hexadecimal digit, rendering the address range more difficult to decipher (see box).

Prefix not a multiple of four
If the prefix length is not a round multiple of four, the binary separation will take place inthe middle of a hexadecimal number. This means that all hexadecimal numbers that startwith the same series of bits will belong to this prefix. The prefix
2001:db8::/61

thus contains all the addresses from2001:0db8:0000:0000:0000:0000:0000:0000

through
2001:0db8:0000:0007:ﬀﬀ:ﬀﬀ:ﬀﬀ:ﬀﬀ

because the hexadecimal numbers 0 through 7 all start with the binary value 0.
For example, the prefix
2001:db8:0:8::/61

contains all the addresses from2001:0db8:0000:0008:0000:0000:0000:0000

through
2001:0db8:0000:000f:ﬀﬀ:ﬀﬀ:ﬀﬀ:ﬀﬀ

because the hexadecimal numbers 8 to f all start with the binary value 1.

With IPv4, it's at least theoretically possible to have a non-contiguous subnet mask. For
instance, with subnet mask 255.255.252.255 the addresses 192.0.2.3 and 192.0.3.3 are in5		

Preparing an IPv6 Address Planthe same subnet, but 192.0.2.3 and 192.0.2.4 aren't. However, non-contiguous subnet
masks have no corresponding prefix length. As IPv6 subnets are defined using prefix
lengths, non-contiguous subnets are not possible with IPv6.
2.3.

/64 Subnets

IPv6 addresses don't have a fixed structure, like the class A/B/C system originally used with IPv4.
However, IPv6 subnets should be /64 prefixes. Other subnet sizes are possible, but may get in
the way of mechanisms such as stateless address autoconfiguration (see section 5.1). So verysmall subnets, such as a point-to-point link, use the same size IPv6 address block as very large
subnets, such as a large Ethernet containing a number of Ethernet switches.
2.4.

Assigning Address Blocks

The original recommendation for assigning IPv6 address space to end users was as follows:•••/48 (65 536 subnets) in the general case, except for very large subscribers/64 (a single subnet) when it is known that one and only one subnet is needed by design/128 (a single address) when it is absolutely known that one and only one device isconnecting

However, RFC 61771 (also known as Best Current Practice 157) changes this, and recommends
using an address block / prefix size tailored to the end user's needs. It also recommends against
giving out single addresses. For instance, a /48 is much more than a home user needs, but a /64
only allows for a single subnet, which may be limiting, if not immediately, then in the future. So
a /56 or /60 may be more appropriate for consumers.
That said, it is important to err on the side of assigning more rather than less, as adding asecond address block or moving to a bigger one is costly. This is especially true when the originalassignment to a medium-sized or larger organisation was a /56. With a /56 assignment, thenetwork will already be fairly large before more address space is needed, so the impact ofchanges will be significant. If the original assignment was a /60, the network would haveoutgrown the assignment when it was much smaller and changes were still much easier tomake.
So a /48 should be used when there is any doubt whether a /56 is sufficient in the long run. ISPs
get much leeway in determining the prefix size they give to their customers up to /48–even in
the case of home users.
ISPs which are LIRs (Local Internet Registries, sometimes called a "RIPE member" in Europe) get
at least a /32, but large ISPs can get much larger address blocks / shorter prefixes, so they canuse a dedicated sub-prefix per region/country where they're active.
In the rest of this document, it is assumed that your organisation has been assigned a /48
address block, and that 16 bits (64 - 48) are therefore available for assigning the addresses tosubnets. If your situation is different, you will need to adapt the calculations in this manual
accordingly.
Based on the above information, the first 48 bits of your IPv6 plan are fixed. In this document,
we use 2001:db8:1234::/48 as an example. This means you can use the /64 prefixes
2001:db8:1234:0000::/64

1 RFCs are available from http://tools.ietf.org/html/

6		

Preparing an IPv6 Address Plan

through
2001:db8:1234:ﬀﬀ::/64

for your network–16 bits in total.
For your own address plan, you will need to replace the numbers in the examples with theprefix allocated to you.
2.5.

Representation of Subdivisions

As the first 48 bits are assigned by a service provider and the last 64 bits are used within eachsubnet, an IPv6 address plan is about bits 48 to 631, the 16 bits available to number subnets. In
this manual, we will subdivide the 16 available bits into groups. We distinguish the following typesof groups:
B: bit is assignable
L: bit is assigned to a location
T: bit is assigned to a use type•••The following notation is used for the assigned bits. The order of the letters here is meaninglessand is only used as an example:
2001:db8:1234:

L

L

L

L

T

T

T

T

B

B

B

B

B

B

B

B

::/ 64Each box represents 1 bit. Four boxes together represent a nibble (four bits) and thus one
hexadecimal digit in the IPv6 address. For the above example, this produces the following
address structure:
2001:db8:1234:LTBB::/64
2001:db8:1234:TLBB::/64

Bits 1-4 are in this example assigned to a location, bits 5-8 are assigned to a use type and bits
9-16 remain available to be assigned to another purpose.

3.

OPTIONS WITHOUT AN ADDRESS PLAN

Small, flat organisations that do not have an internal organisational structure (with several
departments within the organisation being authorised to assign IP addresses) or technicalstructure (distinguishing between various categories of use types and networks) can workwithout an address plan, instead assigning a random free IPv6 address as network host.
A disadvantage is that it can be difficult to recognise networks based on their address because
this method lacks structure. For this reason, we recommend preparing an address plan.
Should you opt to work without an address plan, we recommend keeping a list of the assigned
networks in a central location, such as an Excel spreadsheet, an internal Wiki page, aconfiguration management database (CMDB) or in the reverse DNS configuration.

1 The IETF numbers bits starting at zero from left (most significant) to right (least significant).

7		Preparing an IPv6 Address Plan

3.1.

Direct Link Between IPv4 and IPv6 Subnets

If the existing IPv4 networks use only /24 subnets (for example, from 203.0.113.0 to203.0.113.255), a direct link can be established between IPv4 addresses and the new IPv6
addresses. In this case, you can include the penultimate number of the IPv4 address (113 in
203.0.113.0/24, for example) in the IPv6 subnet. The IPv6 address will then be
2001:db8:1234:113::/64.
Such an IPv4-to-IPv6 transition could appear as follows:
198.51.100.0/24
2001:db8:1234:100::/64
203.0.113.0/24

192.0.2.0/24

2001:db8:1234:113::/64

2001:db8:1234:2::/64

In this address plan, the link between the existing IPv4 networks and the IPv6 networks is
immediately visible. However, this scheme only works well when IPv4 subnets are /24s.
For vital equipment, such as servers and routers, it may be practical to use the last number of
the IPv4 address in the IPv6 address too. The IPv4 address 192.0.2.123, for example, would
become the IPv6 address 2001:db8:1234:2::123.
Should you choose this option, we recommend keeping a list of the assigned networks in acentral location, such as an Excel spreadsheet, an internal Wiki page or in the reverse DNS
configuration.
The reason this approach only works with /24 IPv4 (sub-)networks is that with a different(sub)net size, the IPv6 subnets can't be /64s while making each IPv4 subnet an IPv6 subnet andvice versa. For instance, with a /28 subnet size in effect, the two addresses 172.31.5.14 and
172.31.5.18 are in different IPv4 subnets (172.31.5.0/28 and 172.31.5.16/28), but when mapped
to 2001:db8:1234:5::14 and 2001:db8:1234:5::18, they would be in the same IPv6 /64. If thesubnet size is larger than /24, like with 10.0.8.250 and 10.0.9.5, which are both in 10.0.8.0/23, theaddresses would map to 2001:db8:1234:8::250 and 2001:db8:1234:9::5, which are indifferent /64s.


3.2.

Note that this is not an example of efficient addressing plan as discussed in chapter 1.

Direct Link Between IPv4 and IPv6 Addresses

If the IPv4 subnet size is not /24, it will be impossible to maintain a direct relationship between
IPv4 and IPv6 subnets. In that case, it can still be useful to include the (whole) IPv4 address in
the IPv6 address. For instance, by giving the system with IPv4 address 192.0.2.123 the IPv6
address 2001:db8:1234:2:192:0:2:123.
Note that there is a variation in IPv6 notation that allows the inclusion of an IPv4 address, but inthis case the IPv4 address must occupy the lowest 32 bits of the IPv6 address, for example:
2001:db8:1234:c0:ﬀ:ee:192.0.2.123

8	

	

Preparing an IPv6 Address PlanHowever, the fact that an address was entered in this form is generally not retained, so whendisplaying network settings, it will generally appear in standard IPv6 notation:

2001:db8:1234:c0:ﬀ:ee:c000:27b
At this point, the relationship with IPv4 address 192.0.2.123 is no longer obvious.

4.

Preparing an Address Plan

When preparing your address plan you have to decide which system to use to assign theavailable addresses to the networks in the organisation. There are a number of convenientmethods for assigning addresses.
The present chapter will describe the possible address plans, using the following example
network:
Core router
Network G(VPN)

Network A

Network B

Network C

Network D

Network E

Network F(Students)(Servers)(Employees)(Servers)(Students)(Guests)

Building 1

4.1.

Building 2

Building 3

Basic Structure of the Address Plan

With the IPv6 protocol, there are so many available addresses that we can create one or moreprimary subnets. We can, for example, assign the addresses per use type or per location, or use
combinations. For example, we may assign the addresses first by use type and then by location.
Once these subnets have been defined, there will still be bits remaining that can be assigned toanother purpose.
Take the example in section 2.5:
2001:db8:1234:

L

L

L

L

T

T

T

T

B

B

B

B

B

B

B

B

::/ 64In this example, 4 bits are assigned to a location (L) and 4 bits are assigned to a use type (T). As
a result, there are 8 bits remaining (B). Following this address plan, with 4 location bits, amaximum of 16 locations can be addressed, with each location having 16 (also 4 bits)
allocatable use types. 8 bits are left to number a maximum of 256 different subnets for eachlocation and use type combination.

9		Preparing an IPv6 Address Plan

IPv6, NAT and Firewalls

4.2.

With IPv4, Network Address Translation (NAT) is widely used to allow multiple hosts to gain
access to the public internet using a single IPv4 address. With IPv6, there is no longer a lack ofaddress space, so using NAT for this purpose is no longer necessary.
A side effect of NAT is that it (mostly) prevents unsolicited packets from the public internet
from reaching hosts residing behind the NAT device. As such, protocols that require two hoststhat both reside behind a NAT to communicate directly (peer-to-peer protocols) need to
employ workarounds to set up communication through NAT. However, IPv6 peer-to-peer
applications, and some applications that aren't obviously peer-to-peer, such as FTP, may not havethese workarounds built in, or they may not be compatible with IPv6. So networks deploying
NAT with IPv6 are likely to see more NAT-related problems than in a similar IPv4 deployment.
Also, there is no RFC describing IPv6 NAT, only IPv6 IPv6-to-IPv6 Network Prefix Translation(RFC 6296, with status "experimental").
To prevent unwanted packets coming in from the public internet from reaching hosts, a stateful
firewall may be employed, in order to make sure that incoming packets match communication
sessions set up by internal hosts. See RFC 4864 for more information.

Router vs Firewall: Location or Use Type First

4.3.

We first need to decide on whether to use location first, and then use type (such as students,
staff, servers, switches, routers, public, etc.), or the other way around. These options are
discussed below.
4.3.1.

Location First

When the location is the primary subnet, each building, department etc. is assigned a number ofdedicated addresses. The emphasis in this case lies on optimisation of the routing tables. All the
networks within a single location will be aggregated to a single route in the routing table, so thatthe routing table will remain compact.
4.3.2.

Use Type First

When the use type is the primary subnet, the routing optimisation described above is not
feasible, because the use types are divided across a number of locations. However, in practicethis will not be a problem with most routers.
The advantage of first grouping all subnets by use type is that it makes it much easier toimplement a security policy. Most firewall policies are based on the type of use and not on thelocation of the network. This is why the firewalls often require only one policy per use type.
4.3.3.

Recommendation

Based on the above information, we recommend use type-based primary subnets, because thisis the easiest way to integrate with existing policies and procedures. Possible reasons forlocation-based primary subnets are:
•
•

4.4.

Some locations will prepare their own address plan
The routers cannot process such a large number of routes without aggregation

Determining the Address Space Required for the Address Plan

Now we need to determine which portion of the 16 bits of available address space (see section2.4) is required for the address plan selected, depending on how many groups of use types andlocations there are. For both, the number of groups determines how many of the 16 bits

10		

Preparing an IPv6 Address Planavailable must be used. One bit can contain two groups (21), 2 bits can contain 4 groups (22),etc. (see the table).
We can calculate the number of groups as follows:
1. First determine the number of locations or use types within your organisation. Count eachlocation or use type as one group.
2. Increase this number by one group (required for the backbone and other infrastructure).
3. If you choose to work with location-based primary subnets, add one extra group for all
networks that do not have a fixed location. These are networks for VPNs and tunnels, forexample.
4. Add one or two groups to allow for future expansion.
To create a practical address plan, the number of blocks into which we divide the address spaceshould be to a power of 2. So we’ll round up the number of groups counted in steps 1 to 4 tothe nearest power of 2. See the table for the number of bits required for each possible numberof groups.
The result is the number of groups in the primary subnet, either by location or by use type. Thismethod is explained using a number of examples. More detailed examples can be found inchapter 5.
Bits

Locations or use types

1

2

2

3 or 43

5-8

4

9 - 16

5

17 - 326

33 - 647

65 - 1288

129 - 2569257 - 51210

513 - 1024

111025 - 2048

122049 - 4096

Example 1: Location-based subnet
In this example, we define the locations as the primary subnets. The number of groups requiredis then as follows:
•
•
•
•
•

Number of locations:	

Backbone and other infrastructure:	

Non-location-based networks:	

Future locations:	

Total:	

11	

	

Three groups
One group
One group
Two groups
Seven groups

Preparing an IPv6 Address Plan

This example network would then appear as follows:ndou nt b tio
No locatoCore router
Network G

Infrastructure(VPN)

Network A

Network B

Network C

Network D

Network E

Network F(Students)(Servers)(Employees)(Servers)(Students)(Guests)

Building 1

Building 2

Building 3

Location 1

Location 2

Location 3

If we round this up to the first power of 2, this results in eight subnets. Incorporating theseprimary subnets into the IPv6 address requires 3 bits (L). This results in the following bit
distribution:L

2001:db8:1234:

L

L

B

B

B

B

B

B

B

B

B

B

B

B

B

::/ 64This leaves 13 available bits (B).
Example 2: Use type-based subnet
In this example we define the use types as the primary subnets. The number of groups requiredis then as follows:••••

Number of use types (staff,students, guests, servers and VPNs):	

Backbone and other infrastructure:	

Future use types:	

Total:	

Five groups
One group
Four groups
Ten groups

This example network would then appear as follows:
Core router
N

(VPN)

VP

Network G

Infrastructure

Network A

Network B

Network C

Network D

Network E

Network F(Students)(Servers)(Employees)(Servers)(Students)(Guests)

Building 1

Building 2

Building 3

Employees
GuestsStudents
Servers12		Preparing an IPv6 Address Plan

If we round this up to the first power of 2, this results in 16 subnets. Incorporating thesesubnets into the IPv6 address requires 4 bits (T) (24 = 16). This leaves 12 available bits (B).
2001:db8:1234:

4.5.

T

T

T

T

B

B

B

B

B

B

B

B

B

B

B

B

::/ 64

Optional Secondary Subnets

The remaining bits can be used for numbering secondary subnetworks within the selected
address plan. If the primary subnets are location-based, multiple networks can be addressed bylocation, whereas if the primary subnets are use type-based, multiple student networks orserver networks can be addressed, for example.
The remaining bits can also be used to combine subnets by location and use type. If the subnet
is location-based, as in example 1, and we create a use type-based secondary subnet, as inexample 2, the result is as follows:
2001:db8:1234:

L

L

L

T

T

T

T

B

B

B

B

B

B

B

B

B

::/ 64In this address plan, there is space for eight locations, each with 16 use types. Within each use
type, there are yet another 512 (29 due to 9 available bits) secondary subnetworks available.
This combination of primary and secondary subnets uses location-based primary subnets. This
will make it easier to optimise routing tables, but it will complicate the design of the security
policy. This is because firewall policies can only be applied on the basis of the first numbers of an
address, while in this example the location is at the start of the address, not the use type.
To facilitate the design process for the security policy, the combination can be reversed bymaking the primary subnet use type-based, as in example 2, and the secondary subnets
location-based, as in example 1. The result is then as follows:
2001:db8:1234:

T

T

T

T

L

L

L

B

B

B

B

B

B

B

B

B

::/ 64In this example, the use type is at the start of the address, making it easier to apply firewall
policies per use type. Since the use type is typically more relevant for security policies than thelocation, we recommend using this system.
4.6.

Double Check

We can check whether the address plan we have created meets our requirements by counting
the number of bits remaining after creation of the primary and secondary subnets. If, forexample, after the creation of use type-based primary subnets containing location-based
secondary subnets we also require multiple student networks at each location, there will haveto be enough bits left to create these.
In the example in section 4.5 there are 9 bits remaining, which results in 512 (29) possible values
per use type per location. This will usually be more than enough.
4.7.

LeewayIf the number of remaining bits is not quite sufficient, this can be compensated for in theassignment of the primary and secondary subnets.
In the above example we used 4 bits for the use types and 3 bits for the locations. That leaves 9
bits, so we can create 512 (29) networks per use type per location.

13	

	

Preparing an IPv6 Address Plan

2001:db8:1234:

T

T

T

T

L

L

L

B

B

B

B

B

B

B

B

B

::/ 64This will be sufficient in most cases. However, it may be that we require 2,048 VPN networks
per location. This can be done by changing the assignment of primary and secondary subnets.
However, the IPv6 address will become more difficult to decipher in hexadecimal format.
Another option is to reserve four groups within the use type subnets for VPN networks. If wesort the numbers of this group of four in binary number groupings (decimal: 0-3, 4-7, 8-11 of
12-15; hexadecimal: 0-3, 4-7, 8-B, C-F) then these can still be covered by a single firewall policy.
The following groups might result:0

Backbone and other infrastructure1Servers2

Future expansion

3

Future expansion

4

Staff

5

Students

6

Guests7

Future expansion

8

VPNs

9

VPNs

A

VPNs

B

VPNs

C

Future expansion

D

Future expansion

E

Future expansion

F

Future expansion

4.8.

Legibility

If there are enough bits remaining, we can use them to make IPv6 addresses more legible. Eachhexadecimal digit in an IPv6 address is equivalent to 4 bits. By choosing an assignment system
based on multiples of 4 bits, each group will correspond to a digit in the IPv6 address.
In the example in this section, we used 3 bits per location and 4 bits per use type. However, thehexadecimal digits in the IPv6 address each represent 4 bits. So if the location or use type only
needs two or three bits, it can be useful to make it 4 bits instead, and make IPv6 addresses
easier to read. For example:
2001:db8:1234:

L

L

L

T

T

T

T

B

B

B

B

B

B

B

B

B

::/ 64

2001:db8:1234:

T

T

T

L

L

L

L

B

B

B

B

B

B

B

B

B

::/ 64

Respectively become:14	

	Preparing an IPv6 Address Plan

2001:db8:1234:

L

L

L

L

T

T

T

T

B

B

B

B

B

B

B

B

::/ 64

2001:db8:1234:

T

T

T

T

L

L

L

L

B

B

B

B

B

B

B

B

::/ 64

The 4 L bits are displayed as one hexadecimal digit in the IPv6 address. The four T bits are also
displayed as one hexadecimal digit. This results in the following IPv6 address structure:
2001:db8:1234:LTBB::/64
Using this system, the location and use type can easily be identified in the IPv6 address. The firstsymbol indicates the location (L) and the second indicates the use type (T).
4.9.

Flexibility for Future Growth

If the number of locations and/or use types may grow in ways that are hard to predict at thetime the address plan is created, it may be beneficial to keep the boundaries between the
different groups of bits as flexible as possible. This can be done using the strategy outlined in
RFCs 1219 and 3531. The downsides of this approach is that a good understanding of bit
manipulation is required, and from time to time, as the boundaries between the fields move,firewall rules and the like need to be updated. Assuming that the location occupies the top bits
and the use type comes next, an address plan with flexible boundaries may start as follows, withfive locations, three use types and two subnets per location/use type:2001:db8:1234:

L

L

L

T

T

B

::/ 64

Then, perhaps the number of subnets per use type goes up from two to ten, requiring four bits:
2001:db8:1234:

L

L

L

T

T

B

B

B

B

::/ 64After this, the number of use types increases to five, requiring a third bit. There are more freebits on the left side, so the use type field grows in that direction:
2001:db8:1234:

L

L

L

T

T

T

B

B

B

B

::/ 64

T

T

B

B

B

B

::/ 64

The number of locations grows to 50, requiring six bits:
2001:db8:1234:

L

L

L

L

L

L

T

The number of use types grows to 13, requiring a fourth bit, which is taken from the rightwhere there are more remaining bits:
2001:db8:1234:

L

L

L

L

L

L

T

T

T

T

B

B

B

B

::/ 64And so on. Note that the L and T fields have gained bits to the right, which means that in order
to avoid renumbering, encoding a number in these bits must be done in a somewhat unusual
way. Please refer to RFC 3531 for more information.
4.10.

Using VLAN Numbers

Another approach is to use VLAN numbers as the subnet number. In networks where mostsubnets are VLANs and thus already have a VLAN number, this simplifies the administration of
VLAN and subnet numbers, because now only one number has to be managed.
15		

Preparing an IPv6 Address PlanVLAN numbers are 12 bits in size, while subnet numbers are 16 bits (assuming a /48 prefix forthe organisation). So it's possible to simply use either of the following approaches:
2001:db8:1234:

V

V

V

V

V

V

V

V

V

V

V

V

B

B

B

B

::/ 64

2001:db8:1234:

B

B

B

B

V

V

V

V

V

V

V

V

V

V

V

V

::/ 64

However, IPv6 addresses are written as hexadecimal, but VLAN numbers are written in decimal.
So the above approaches require conversion between hex and decimal, obscuring therelationship between the VLAN and subnet numbers and thereby negating the advantage ofsimplicity.
A preferable approach is to take the decimal VLAN number, and use it in the place of thehexadecimal subnet number. So VLAN 2783 simply becomes subnet 2001:db8:1234:2783::/64.
Note that this leaves the subnet numbers above 4095 as well as any subnet number with one
or more letters in it available for additional subnets that aren't tied to a VLAN. The table shows
both options and the two hexadecimal variations.
VLAN ID

IPv6 decimal

IPv6 hexadecimal (high)IPv6 hexadecimal (low)1

2001:db8:1234:0001::/ 64

2001:db8:1234:0010::/ 64

2001:db8:1234:0001::/ 64

12

2001:db8:1234:0012::/ 64

2001:db8:1234:00c0::/ 64

2001:db8:1234:000c::/ 64

2783

2001:db8:1234:2783::/ 64

2001:db8:1234:adf0::/ 64

2001:db8:1234:0adf::/ 64

4094

2001:db8:1234:4094::/ 64

2001:db8:1234:ffe0::/ 64

2001:db8:1234:0ffe::/ 64

In this approach, as the use type and location do not appear in the IPv6 address, it will not be
possible to optimise the security policies and routing tables unless this was planned for whenassigning VLAN IDs. With hexadecimal encodings, four bits remain free for other purposes, suchas encoding the location.
4.11.

VLAN Numbers That Encode Location/Use TypeIt is also possible to combine the encoding of location and use type with using VLAN numbers.
Some organisations have already included a location and/or use type description in their VLAN
numbering plan. If this is the case, you might consider transferring these numbers directly to the
IPv6 addressing system. In this case, it's easiest to stick to the 4-bit boundaries and not use
numbers higher than 9 in one of the following schemes.
This is an example of encoding location first and then use type into the VLAN number and thenthe VLAN number into the subnet bits of the IPv6 address:
2001:db8:1234:

V

V

V

V

V
↓
L

V
↓
L

V
↓
L

V
↓
L

V
↓
T

V
↓
T

V
↓
T

V
↓
T

V
↓
B

V
↓
B

V
↓
B

V
↓
B

::/ 64

And this is an example of encoding the use type first and then the location into the VLAN
number and then the VLAN number into the subnet bits of the IPv6 address:
2001:db8:1234:

V

V

16	

V

V

	

V
↓
T

V
↓
T

V
↓
T

V
↓
T

V
↓
L

V
↓
L

Preparing an IPv6 Address Plan

V
↓
L

V
↓
L

V
↓
B

V
↓
B

V
↓
B

V
↓
B

::/ 64

Unfortunately, such strict subdivision of the bits and the imposed decimal/hex compatibility
reduce the number of usable subnets significantly. So only small to medium sized organisations
will be able to stick to such a numbering plan as the network grows.
4.11.1. Reversing VLAN Notation in an IPv6 Structure

There are also options for reversing previously defined VLAN notations. If, for example, theVLAN numbers are assigned first by location and then by use type, it is still possible to assign
the IPv6 addresses in the reverse order: first by use type and then by location.
In the following example of a VLAN structure, the hexadecimal notation of the VLAN number,
location and use type is placed between parentheses:
VLAN number

Location

Use Type

0001

(001)

0

(0)

1

(01)

0529

(211)

2

(2)

17

(11)

4094

(FFE)

15

(F)

254

(FE)

In this example, the first 4 bits of the VLAN number identify the location. The remaining 8 bits
describe the use type. By copying this directly to the IPv6 address, we are able to optimise therouting table, but not the security policy. The reason for this is that the location is at the start of
the address while the use type follows it. However, if we wish to use the IPv6 addresses tooptimise the security policies, the use type has to be at the start of the address.
To arrange this, we can move the first 4 bits of the VLAN number (which describe the location)
to the back to become the last 4 bits of the IPv6 subnet. The last 8 bits of the VLAN number(which describe the use type) can be placed in front of these.
4.11.2. Hexadecimal Notation

Hexadecimal notation is further explained using the example below. The hexadecimal notationof the VLAN number, location and use type is placed between parentheses.
VLAN number

Location

Use type

IPv6 hexadecimal

0001

(001)

0

(0)

1

(01)

2001:db8:1234:0010::/ 64

0529

(211)

2

(2)

17

(11)

2001:db8:1234:0112::/ 64

4094

(FFE)

15

(F)

254

(FE)

2001:db8:1234:0fef::/ 64

4.11.3. Decimal Notation

A similar notation system can be used if the VLAN number is divided decimally. If, for example,
the first two digits indicate the location and the last two digits the use type, this can be reversedin the IPv6 address. For example:
VLAN number

Location

Use Type

IPv6 decimal

0001

00

01

2001:db8:1234:0100::/ 64

0529

05

29

2001:db8:1234:2905::/ 64

4094

40

94

2001:db8:1234:9440::/ 6417		

Preparing an IPv6 Address Plan

Addressing Point-to-point Links

4.12.

If you use point-to-point links, using a /64 address may present problems in combination withcertain router configurations. In some cases, unused addresses in the /64 system may bebounced back by the routers on either side of the link. Data packets sent to this address willthus be sent back and forth between the routers like ping pong balls. This places an unwanted
burden on the network. It might therefore, be practical in some cases to configure a prefix
longer than /64 for these links.



Please note: using a subnet prefix size other than /64 goes against RFC 4291 1.

But if not /64, what is the appropriate subnet size for point-to-point links?
•

•

•
•

/127 is possible because IPv6 doesn't have any broadcast addresses. However, the allzeroes address in each subnet is the "all routers anycast address", which means that all
routers are supposed to receive packets at that address. Some router vendors do not
implement this feature, so /127 subnets work on their routers. But problems may arise
when this equipment is replaced with that from another vendor.
/126 allows the all-zeroes address to be skipped. However, the highest 128 addresses inany subnet are also reserved for various anycast addresses (RFC 2526). But in practice this is
typically not problematic.
/120 makes it possible to avoid all reserved anycast addresses.
/112 makes it possible to avoid reserved anycast addresses and has the advantage that theentire four-digit hex value after the last colon in the IPv6 address identifies systems within
the subnet.

So /112 seems like the best non-/64 alternative. But it may also be useful to minimize thenumber of addresses in a subnet to avoid neighbor cache exhaustion attacks, where an attacker
scans all the addresses in a subnet and routers must execute Neighbor Discovery for all thoseaddresses, exhausting their resources. So an alternative may be a /126 or /120 but reservea /112 for human readability or even an entire /64 so it's still possible to switch to /64 at a later
date.
4.13.

EUI-64 Addressing

On subnets with only routers present, it can be useful to have the routers generate the lower
64 bits of their IPv6 address in that subnet automatically. This way, there is no need to track
which router has which address. It may be possible to configure the use of "EUI-64" (the 64-bit
form of an Ethernet MAC address) addressing. Routers will then generate an IPv6-address fromtheir MAC address similar to how hosts may generate the lower 64 bits of their IPv6 addressfrom their MAC address when stateless address autoconfiguration is used. Like stateless address
autoconfiguration, EUI-64 addressing is only possible on /64 subnets.
The figure below shows a subnet containing wo Cisco routers configured with "ipv6 address
2001:db8:1234:419::/64 eui-64" on the interface connecting to the subnet. Despite the identicalconfiguration, each router configures a unique address.

1 http://tools.ietf.org/html/rfc4291#section-2.5.4

18	

	

Preparing an IPv6 Address Plan

5.

MANAGING AND ADDRESSING HOSTS

Once you have an address plan for the IPv6 networks, you can proceed to address the hosts inthe network. There are three common methods for doing this:•••Stateless address autoconfiguration
Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
Manual configuration

We recommend automatic configuration via stateless address autoconfiguration (sometimes
unofficially abbreviated as SLAAC) or DHCPv6 for most clients because this makes
management considerably easier. If properly implemented, it also increases the privacy of theusers. Manual configuration is recommended only for equipment such as routers, switches,firewalls and servers.
5.1.

Stateless Address Autoconfiguration

Stateless address autoconfiguration is the simplest way to link hosts to an IPv6 network. The
router sends “Router Advertisements” (RAs) and the hosts use the information in the RA in
combination with their MAC address to assign an IPv6 address. Ethernet MAC addresses are 48
bits, but these are extended to 64 bits first by adding the bits FFFE in the middle, creating a 64bit Extended Unique Identifier (EUI-64). Then, the unique/local bit in the MAC address is flipped
to avoid manually configured addresses from looking like addresses derived from a globallyunique MAC address. The lower 64 bits in an IPv6 address are known as the "interface
identifier". For example, the MAC address 04:0c:ce:e9:38:60 results in the interface identifier
60c:ceff:fee9:3860.
An RA may contain multiple prefixes. If multiple routers on a single subnet send RAs, the hosts
will listen to all RAs sent by all routers and configure addresses in all prefixes in all RAs. Thisfeature can be used to incorporate a degree of redundancy.
5.2.

Privacy Addresses

Current mainstream operating systems use privacy extensions in addition to EUI-64 basedstateless address autoconfiguration. These privacy extensions avoid the situation where a host
may connect to different IPv6 networks at different times and is then tracked by remotesystems that observe the same MAC address in connections made from those different
networks. The privacy extensions work by using a random number as the interface identifier
rather than an EUI-64. A new random number is generated every 24 hours or whenever thesystem (re)connects to a network.
Typically, hosts generate a MAC based address as well as a privacy address, and then use theprivacy address for outgoing connections. The MAC address based address may be used as astable address for receiving incoming connections.

19		Preparing an IPv6 Address Plan

Dynamic Host Configuration Protocol for IPv6 (DHCPv6)

5.3.

The use of privacy addresses can be problematic if network managers wish to trace who isusing which IPv6 address and when. The solution is to use centrally coordinated address
assignment via DHCPv6. Until a few years ago Mac OS X didn't support DHCPv6. However, in
Mac OS X 10.7 DHCPv6 support was added. Windows has supported DHCPv6 as ofWindows Vista. Today all mainstream operating systems support DHCPv6, but DHCPv6
software may not be installed by default on all Linux and BSD distributions.
DHCPv6 can provide IPv6 addresses as well as other information, such as nameserver
addresses, similar to how IPv4 DHCP works. It can be deployed in two ways:••

DHCPv6 is used to hand out IPv6 addresses as well as other information.
Stateless address autoconfiguration is used to configure IPv6 addresses, DHCPv6 is used tohand out other information.

Two flags in router advertisements determine which option is selected by hosts. For this reason,
and also because DHCPv6 doesn't provide a default gateway address, IPv6 routers must always
send router advertisements to hosts, even when stateless address autoconfiguration isn't used.
Note that depending on how RAs are configured, DHCPv6 and stateless address
autoconfiguration may be active at the same time, resulting in hosts obtaining two addresses,
three if privacy extensions are used.
If addresses are assigned with DHCPv6, it is recommended to program the switches so thathosts can only use the addresses assigned to them via DHCPv6.



5.4.

Please note: this is not standard for either IPv4 or IPv6. Many suppliers have
implemented their own security policies for IPv4. There are only a few switches available
that offer this security with IPv6. So then the only remedy in case of problems is tracing
the MAC address of the misbehaving system.

Manual Address Configuration

We recommend manually assigning static IPv6 addresses only for equipment such as routers,
switches, firewalls and servers. Automatic configuration of such equipment will lead to problems
in the long run. For example, if the network adaptor on a server is replaced, the statelessaddress autoconfiguration address of that server will also change, and there is a major risk thatthe person replacing the network adaptor will forget to modify the DNS entries for the server.
To increase the traceability of vital equipment, we recommend incorporating all or part of the
IPv4 address into the IPv6 address. This is explained in more detail in section 3.1 and section 3.2.
5.5.

Router Advertisement Guard

Sometimes incorrectly configured (home) routers and hosts to send out IPv6 router
advertisements advertising non-working IPv6 connectivity. As many hosts prefer IPv6
connectivity (when available) over IPv4 connectivity, this means that destinations that have an
IPv6 address in the DNS become unreachable. When this happens by accident, it's a nuisance.
It's also possible that RAs are maliciously injected to reroute traffic so it can be observed ormanipulated.
RFC 6105 proposes Router Advertisement Guard, a system that prevents undesired RAs fromreaching IPv6 hosts. RA Guard is a feature that is implemented in layer 2 devices (i.e., Ethernet
switches). These filter out RAs that come from devices that have no business sending them,while allowing through the RAs from the "real" IPv6 router or routers.

20		

Preparing an IPv6 Address Plan


5.6.

When buying Ethernet switches and Wi-Fi base stations, investigate whether they
support RA Guard.

DNS Considerations

DNS addresses are the addresses that are typed in most frequently. As such, it's useful for them
to be short. They appear in many configuration files locally, and if a DNS server hosts one ormore domains, its address will also be listed in the configurations of far away servers. This makes
it important that DNS addresses are stable over time. With these two considerations in mind,
it's useful to give each DNS server its own /64 subnet, with a short manually configured
address. For instance:
DNS1: 2001:db8:1234:a::53
DNS2: 2001:db8:1234:b::53
Manual configuration of a static address removes dependencies from DHCPv6, stateless address
autoconfiguration and the server's MAC address. Having a separate /64 allows the server to be
moved physically without the need to renumber; the entire subnet simply moves with theserver.
With IPv4, it's standard practice to generate a DNS zone file with a name for each possible
address. So without further action, any host that is connected to the network has a name in the
DNS–although it may be an ugly one.
With IPv6, this is no longer possible, as the number of addresses per address block is way toolarge. In the case of manual configuration of addresses, it is of course no problem to add theaddresses in question to the DNS. With DHCPv6, either the DHCPv6 server can be configured
to hand out the same address to a given system every time, so that address can be entered in
the DNS. However, this is a lot of work. A better solution is to configure the DHCPv6 server to
do a dynamic DNS update whenever it gives out an address lease. But it is straightforward togenerate DNS names for the entire pool of addresses used by the DHCPv6 server.
With stateless address autoconfiguration, hosts create their own addresses. In the case of MAC
address based addresses of fixed location machines, it's possible to add their addresses to the
DNS manually. But for mobile hosts and privacy addresses, this is not workable. It is possible torun a dynamic DNS (RFC 2136) client on such hosts, but those clients need to have the rightsettings and may not update the reverse DNS.
As a result of the above, it is very common for IPv6 hosts to not have a valid reverse DNS
name. As such, it is not recommended to check for reverse DNS name as part of access
restrictions.

21		Preparing an IPv6 Address PlanACKNOWLEDGEMENTS
This manual was produced with the assistance of the following people, whom we would like tothank:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•

Roel Hoek (University of Twente)
Jeroen van Ingen Schenau (University of Twente)
Magda Pattiapon (RUG)
Mente Heemstra (RUG)
Rogier Spoor (SURFnet)
Wim Biemolt (SURFnet)
Niels den Otter (SURFnet)
Maurice van den Akker (SURFnet)
Jan Michielsen (SURFnet)
Thejo van Vlaanderen (Routz Group)
Joost TholhuijsenPeter Verhage (HZ University of Applied Sciences)
Sander Steffann (text version 1)
Miguel Bastos and Nathalie Trenaman (RIPE NCC) (design)
Olly Pekelharing (English translation version 1)
Iljitsch van Beijnum (text version 2)

22	

	

Preparing an IPv6 Address PlanAPPENDIX: DETAILED EXAMPLESThis appendix shows several more detailed examples of the address plan options explained in
section 4.1 and later.

Assigning by Use Type Only
A use type based subnet has been adopted in which the following groups are distinguished:•••

Number of use types (students, staff, guests, servers):	

Backbone and other infrastructure:	

Total:	

Four groups
One group
Five groups

If we round this up to the first power of 2, this results in eight primary subnets. Incorporatingthese groups into the IPv6 address requires 3 bits (23 = 8). With three unused groups, there isenough space for future expansion.
We have used 3 of the available 16 bits; as a result, 13 still remain. We decide not to divide
these into secondary subnets. To increase legibility, we use 4 bits per use type so that 12 bits
remain. This leaves address space for 4096 (212) possible networks per use type. Now there are
12 bits still available:
2001:db8:1234:

T

T

T

T

B

B

B

B

B

B

B

B

B

B

B

B

::/ 64This results in the following address structure:
2001:db8:1234:TBBB::/64
The table below illustrates this:Use type (T)Assignable (B)Network

Infrastructure (0)02001:db8:1234:0000::/ 64

Infrastructure (0)12001:db8:1234:0001::/ 64

Infrastructure (0)122001:db8:1234:000c::/ 64

Infrastructure (0)100

2001:db8:1234:0064::/ 64Students (1)02001:db8:1234:1000::/ 64Students (1)12

2001:db8:1234:100c::/ 64Students (1)321

2001:db8:1234:1141::/ 64

Etc.

Assigning by Use Types and Locations
We want to set up a use type based primary subnet and a location based secondary subnet.
The following use types are distinguished:•••

Number of use types (students, staff, guests, servers):	

Backbone and other infrastructure:	

Total:	

Four groups
One group
Five groups

If we round this up to the first power of 2, this results in eight groups. Incorporating thesegroups into the IPv6 address requires 3 bits (23 = 8). With three unused groups, there is enoughspace for future expansion.
23	

	

Preparing an IPv6 Address Plan

This example is based on 35 locations. If we use 6 bits, we will have address space for 64 (26)locations, which is more than enough.
We have now assigned 9 bits to the primary and secondary subnets, and so 7 remain. We canuse these 7 bits to create 128 (27) networks per use type per location.
In this example, we decide not to make any modifications to improve legibility. We recommendthat you do make such modifications in practice, but in this example we wish to demonstrate
the impact of a sub-optimum address plan on legibility.
We now have the following IPv6 address structure:
2001:db8:1234:

T

T

T

L

L

L

L

L

L

B

B

B

B

B

B

B

::/ 64This results in the following example addresses. It is obvious that the groups cannot be traced in
the address:
Use type

Location

Assignable

Network

Infrastructure (0)Non-location-based (0)02001:db8:1234:0000::/ 64

Infrastructure (0)Non-location-based (0)1

2001:db8:1234:0001::/ 64

Infrastructure (0)Non-location-based (0)2

2001:db8:1234:0002::/ 64

Infrastructure (0)Location 1

0

2001:db8:1234:0080::/ 64

Infrastructure (0)Location 35

0

2001:db8:1234:1180::/ 64Students (1)Non-location-based (0)02001:db8:1234:2000::/ 64Students (1)Location 1

12

2001:db8:1234:208c::/ 64Students (1)Location 35

92001:db8:1234:3189::/ 64

Etc.

Improving Legibility
Although the assignment method used in the previous example may well function perfectly, it
makes it very difficult to decipher addresses. To improve legibility, we will divide the addresses
into groups of 4 bits, as explained in section 4.8.
We will use 4 bits for the use type and 8 bits for the locations. This leaves us 4 bits to create
networks per use type per location. It is important to check whether these 4 bits are sufficient.
An example of a situation where 4 bits would be insufficient is if there are to be more than 16(24) student networks per location. We can then use the extra leeway created by using an extra
bit for the use type as described in section 2.5.
This results in the following situation:
2001:db8:1234:

T

T

T

T

L

L

L

L

L

L

The following address structure is created:	

2001:db8:1234:TLLB::/64

The table below illustrates this:24		Preparing an IPv6 Address Plan

L

L

B

B

B

B

::/ 64

Use type

Location

Assignable

Network

Infrastructure (0)Non-location-based (0)02001:db8:1234:0000::/ 64

Infrastructure (0)12001:db8:1234:0001::/ 64

Infrastructure (0)2

2001:db8:1234:0002::/ 64

Infrastructure (0)Location10

2001:db8:1234:0010::/ 64

Infrastructure (0)Location35

0

2001:db8:1234:0230::/ 64Students (1)Non-location-based (0)02001:db8:1234:1000::/ 64Students (1)Location 1

12

2001:db8:1234:101c::/ 64Students (1)Location 35

92001:db8:1234:1239::/ 64

Etc.

25	

	

Preparing an IPv6 Address PlanSURFnet
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PO Box 19035
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The Netherlands
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F +31 (0)30 2 305 329
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