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IPv6 global unicast address range

Hi all experts.

I just wanted to confirm my concept.

The global unicast address is written like this

2000::/3 does it mean that following are also valid global addresses


1) 3000::/3

2) 4000::/3

3) 8000::/3

4) 9000::/3

Am i right ?

2 ACCEPTED SOLUTIONS

Accepted Solutions

Re: IPv6 global unicast address range

Hello John,

It is not correct. The global space address's  first three digit must be 001 (Binary 2) and the subnet mask is /3 means

you can vary bits after first three.

Means possible address will be 2000 (0010), 3000(0011)  but can not be 5000 (0101)

But current allocation policy from IANA is 2000/3 to different registry

IPv6 Prefix Allocation Reference Note
0000::/8Reserved by IETF[RFC4291][1][5][6]
0100::/8Reserved by IETF[RFC4291]
0200::/7Reserved by IETF[RFC4048][2]
0400::/6Reserved by IETF[RFC4291]
0800::/5Reserved by IETF[RFC4291]
1000::/4Reserved by IETF[RFC4291]
2000::/3Global Unicast[RFC4291][3]
4000::/3Reserved by IETF[RFC4291]
6000::/3Reserved by IETF[RFC4291]
8000::/3Reserved by IETF[RFC4291]
A000::/3Reserved by IETF[RFC4291]
C000::/3Reserved by IETF[RFC4291]
E000::/4Reserved by IETF[RFC4291]
F000::/5Reserved by IETF[RFC4291]
F800::/6Reserved by IETF[RFC4291]
FC00::/7Unique Local Unicast[RFC4193]
FE00::/9Reserved by IETF[RFC4291]
FE80::/10Link Local Unicast[RFC4291]
FEC0::/10Reserved by IETF[RFC3879][4]
FF00::/8Multicast[RFC4291]

Hope it is useful

Regards

Mahesh

Cisco Employee

Re: IPv6 global unicast address range

Hello Jonn,

Don't worry, you are welcome with all your questions and I consider none of them to be stupid.

Since the range 2000::/3 to E000::/3 is given under the heading global 
unicast addresses, doesnt it mean, its saying the global unicast 
addresses can fall under this range ?

Strictly speaking, yes, a global unicast address can fall into this range but this range is not exhaustive - there are also other ranges defined for global unicast addresses. For example, the IPv6-mapped IPv4 addresses in the form ::FFFF:A.B.C.D,  like, ::FFFF:192.0.2.24, are also global unicast IPv6 addresses though  they do not fall into the range of the addresses you have quoted.

Actually, I object to the last range you quoted - E000::/3. If given in this form, the total range starts on the address E000:: and ends on IPv6 address all set to FF. Thus, it clearly overlaps with the multicast range FF00::/8.

My actual question was that, does the following

1) 3000::/3

2) 4000::/3

fall in global space ? or is it correct that for global address the starting bits must be 001 ???

Yes, they both fall to global unicast space but not because they start with 001 but rather because this range has not been allocated for any other purpose.

Global unicast IPv6 prefixes that are being currently allocated by IANA are indeed from the 2000::/3 block, so they all start with 001, but that was simply a management decision that the allocation will start with this range. It could have been any other reasonable range in the space of global unicast addresses.

Your ranges 3000::/3, 4000::/3, 8000::/3, 9000::/3 are global 
unicast  but they are not, with the exception of the address 3000::/3, 
allocated  from the original prefix 2000::/3.

Well, I just wanted to say that these addresses are not "from the same IPv6 network" but rather they constitute separate "IPv6 networks":

3000::/3 is a host address and falls into the IPv6 prefix 2000::/3

4000::/3 is a network address itself

8000::/3 is a network address itself

9000::/3 is a host address and falls into the IPv6 prefix 8000::/3

Best regards,

Peter

12 REPLIES

Re: IPv6 global unicast address range

Hello John,

It is not correct. The global space address's  first three digit must be 001 (Binary 2) and the subnet mask is /3 means

you can vary bits after first three.

Means possible address will be 2000 (0010), 3000(0011)  but can not be 5000 (0101)

But current allocation policy from IANA is 2000/3 to different registry

IPv6 Prefix Allocation Reference Note
0000::/8Reserved by IETF[RFC4291][1][5][6]
0100::/8Reserved by IETF[RFC4291]
0200::/7Reserved by IETF[RFC4048][2]
0400::/6Reserved by IETF[RFC4291]
0800::/5Reserved by IETF[RFC4291]
1000::/4Reserved by IETF[RFC4291]
2000::/3Global Unicast[RFC4291][3]
4000::/3Reserved by IETF[RFC4291]
6000::/3Reserved by IETF[RFC4291]
8000::/3Reserved by IETF[RFC4291]
A000::/3Reserved by IETF[RFC4291]
C000::/3Reserved by IETF[RFC4291]
E000::/4Reserved by IETF[RFC4291]
F000::/5Reserved by IETF[RFC4291]
F800::/6Reserved by IETF[RFC4291]
FC00::/7Unique Local Unicast[RFC4193]
FE00::/9Reserved by IETF[RFC4291]
FE80::/10Link Local Unicast[RFC4291]
FEC0::/10Reserved by IETF[RFC3879][4]
FF00::/8Multicast[RFC4291]

Hope it is useful

Regards

Mahesh

New Member

Re: IPv6 global unicast address range

Thanks alotttttttttttttttttttttttttttt :-)

New Member

Re: IPv6 global unicast address range

Can you kindly also share the link from which the table was posted ?

Thanks in advance

Cisco Employee

Re: IPv6 global unicast address range

Hi Jonn,

The global unicast address is actually defined in a different way: The RFC 4291 in the Section 2.4 states:

      Address type         Binary prefix        IPv6 notation   Section
      ------------         -------------        -------------   -------
      Unspecified          00...0  (128 bits)   ::/128          2.5.2
      Loopback             00...1  (128 bits)   ::1/128         2.5.3
      Multicast            11111111             FF00::/8        2.7
      Link-Local unicast   1111111010           FE80::/10       2.5.6
      Global Unicast       (everything else)

So the global unicast is everything that has not been allocated for different purposes. It is necessary to keep track of different other RFCs that allocate further address spaces. For example, this table lacks the Unique Local Address space FC00::/7 allocated for addressing private networks.

The IPv6 space 2000::/3 is actually the space currently used for public IPv6 prefix allocation but it is not the only global unicast space.

The prefix 2000::/3 is actually about all possible prefixes whose highest 3 bits are identical with the highest three bits in the first byte which is 0x20 = 32. In this number, the highest 3 bits are set to 001, so the resulting total range in the first byte is from 32 to 63, in hex from 0x20 to 0x3f, yielding the range 2000::/3 - 3fff::/3.

Your ranges 3000::/3, 4000::/3, 8000::/3, 9000::/3 are global unicast but they are not, with the exception of the address 3000::/3, allocated from the original prefix 2000::/3.

Please feel welcome to ask further.

Best regards,

Peter

EDIT: I see that the issue has already been resolved Mahesh, you're as fast as a CRS-3

Re: IPv6 global unicast address range

Thanks Peter

Regards

mahesh

New Member

Re: IPv6 global unicast address range

hi,,

Thanks alot for providing feedback, Peter and Mahesh,

during my research, while checking ipv6 configuration guide, i found the following lines in the following link

http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-addrg_bsc_con.html

Figure 1     Aggregatable Global Address Format

Addresses with a prefix of 2000::/3 (001) through E000::/3 (111) are  required to have 64-bit interface identifiers in the extended universal  identifier (EUI)-64 format. The Internet Assigned Numbers Authority  (IANA) allocates the IPv6 address space in the range of 2000::/16 to  regional registries.

Does it makes my assumption correct then ???

Kindly help me out

Cisco Employee

Re: IPv6 global unicast address range

Hello Jonn,

Addresses with a prefix of 2000::/3 (001) through E000::/3 (111) are required to have 64-bit interface identifiers in the extended universal  identifier (EUI)-64 format. The Internet Assigned Numbers Authority  (IANA) allocates the IPv6 address space in the range of 2000::/16 to  regional registries.

Does it makes my assumption correct then ???

Which assumption exactly?

The statement you have quoted has to be interpreted in this way: If the topmost bits of the IPv6 prefix are in the range 001 till 111 (i.e. not 000), then the lower 64 bits are required to be set to the modified EUI-64. That's it - this statement does not say which additional addresses are global unicast or some other type, or which addresses fall under the prefix 2000::/3 you have originally asked about. This statement only specifies the format of the low 64 bits depending on the value of the topmost 3 bits.

Best regards,

Peter

New Member

Re: IPv6 global unicast address range

Dear Peter,

kindly dont mind if i ask or press something stupid, i just want to clear my concept.

Since the range 2000::/3 to E000::/3 is given under the heading global unicast addresses, doesnt it mean, its saying the global unicast addresses can fall under this range ? plus i read your reply, you also mentioned that anything else then what iana has currectly allocated/reserved falls in global unicast addresses.

My actual question was that, does the following

1) 3000::/3

2) 4000::/3

fall in global space ? or is it correct that for global address the starting bits must be 001 ???

Kindly guide me

EDIT: Sorry i wanted to ask before also, i really didnt get your following statement, pls help me to understand

Your ranges 3000::/3, 4000::/3, 8000::/3, 9000::/3 are global unicast  but they are not, with the exception of the address 3000::/3, allocated  from the original prefix 2000::/3.

Cisco Employee

Re: IPv6 global unicast address range

Hello Jonn,

Don't worry, you are welcome with all your questions and I consider none of them to be stupid.

Since the range 2000::/3 to E000::/3 is given under the heading global 
unicast addresses, doesnt it mean, its saying the global unicast 
addresses can fall under this range ?

Strictly speaking, yes, a global unicast address can fall into this range but this range is not exhaustive - there are also other ranges defined for global unicast addresses. For example, the IPv6-mapped IPv4 addresses in the form ::FFFF:A.B.C.D,  like, ::FFFF:192.0.2.24, are also global unicast IPv6 addresses though  they do not fall into the range of the addresses you have quoted.

Actually, I object to the last range you quoted - E000::/3. If given in this form, the total range starts on the address E000:: and ends on IPv6 address all set to FF. Thus, it clearly overlaps with the multicast range FF00::/8.

My actual question was that, does the following

1) 3000::/3

2) 4000::/3

fall in global space ? or is it correct that for global address the starting bits must be 001 ???

Yes, they both fall to global unicast space but not because they start with 001 but rather because this range has not been allocated for any other purpose.

Global unicast IPv6 prefixes that are being currently allocated by IANA are indeed from the 2000::/3 block, so they all start with 001, but that was simply a management decision that the allocation will start with this range. It could have been any other reasonable range in the space of global unicast addresses.

Your ranges 3000::/3, 4000::/3, 8000::/3, 9000::/3 are global 
unicast  but they are not, with the exception of the address 3000::/3, 
allocated  from the original prefix 2000::/3.

Well, I just wanted to say that these addresses are not "from the same IPv6 network" but rather they constitute separate "IPv6 networks":

3000::/3 is a host address and falls into the IPv6 prefix 2000::/3

4000::/3 is a network address itself

8000::/3 is a network address itself

9000::/3 is a host address and falls into the IPv6 prefix 8000::/3

Best regards,

Peter

New Member

Re: IPv6 global unicast address range

Thanks alot Peter, thanks alot, i really appreciate it.

Thanks again

Cisco Employee

Re: IPv6 global unicast address range

Jonn,

You are heartily welcome.

Best regards,

Peter

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