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# ipv6 noob question

Member Posts: 54 ■■■□□□□□□□
Hey everyone I read many things about IPV6 but I don't get what / notation and number after it means i mean like this:

2000::/3
FE80::/10

can you tell me what it's mean ?

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Mod Posts: 11,962 Mod
It means the same thing it means in IPv4. Mask length.
An expert is a man who has made all the mistakes which can be made.
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Member Posts: 1,340 ■■■■□□□□□□
It is CIDR notation. Basically, it means the same thing as in IPv4.

2000::/3

The first 3 bits of the address are network bits. This example is the Global Unicast range, which is addresses that are Globally (worldwide) Unique and can be assigned to individual IPv6 nodes. Since Heaxdecimal (which IPv6 uses) is base 16, each letter/number is 4 binary bits (2^4 = 16). In this case, anything starting with 001X in binary is part of that range. That would be 0010 (2XXX) and 0011 (3XXX).

FE80::/10

This one (Link Local Unicast) is a bit interesting...The first 10 bits are network bits. Anything starting with 1111 (F) 1110 (E) 10__ (8,9,A,B) would be in that range. The interesting part with this range is that (for some inexplicable reason) the RFC says that the next 54 bits are to be set to all zeroes, so it could have just as easily been FE80::/64.
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Member Posts: 54 ■■■□□□□□□□
how its say mask length ?
2000::/3
so what is the address space
2000:0000:0000:0000:0000:0000:0000:0000 - 2000:0000:0000:0000:E000:0000:0000:0000
?
I mean in ipv4 /24 says how many 1 their is in subnet mask
so /3 means it has 3 bits on ?

i mean how you calculate the address range ??
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Member Posts: 54 ■■■□□□□□□□
nvm thx i think i got it
:P
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Member Posts: 62 ■■□□□□□□□□
Here's my two cents.

The full 128 bit address has:
8 sections which have four hex values (nibbles) in each section: (0000.0000.0000.0000) * 8 = 128 bits
These sections are separated by a total of seven colons.

Using HEX Characters this 128 bit address will look as follows: <---- each zero equals 4 bits (nibble) aka HEX Characters.

0000:0000:0000:0000:0000:0000:0000:0000 <---- 128 bits: (This is how we usually see an IPv6 address.)

>> Possible HEX values are: (0.1.2.3.4.5.6.7.8.9.A.B.C.D.E.F)
>> A nibble equals 4 bits with the following values: (8 4 2 1)

>> This becomes the HEX value of "2". <--- See the first nibble: (1st two bits "off" and the 3rd bit "on").

It has been agreed that all IPv6 primary internet addresses will come from the 2001::/16 subnet! <--- (Prefix).
>> Did you know that 85% of the IPv6 address range has been reserved for the future.

In simple terms the first 64 bits are intended to be reserved for the network address.
The last 64 bits have been reserved for the Host address. <

[ Global Scope (64 bits) + Link-Local Scope (64bits) ] = 128 bits.

To answer your question the /X value defines how many bits are being consumed by the full network address.
>> The spread between the /x value and the total network bits available (64) will be represented as consecutive "0s" or "::".

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Member Posts: 1,340 ■■■■□□□□□□
niba10 wrote: »
how its say mask length ?
2000::/3
so what is the address space
2000:0000:0000:0000:0000:0000:0000:0000 - 2000:0000:0000:0000:E000:0000:0000:0000
?
I mean in ipv4 /24 says how many 1 their is in subnet mask
so /3 means it has 3 bits on ?

i mean how you calculate the address range ??

2000:0000:0000:0000:0000:0000:0000:0001 (2000::1) to 3FFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFE

The bits are counted from left to right (MSB to LSB). An IPv6 Address is 128 bits (vs. 32 bits for IPv4), so /3 means 3 bits for the Network ID. While, IPv6 doesn't use subnet masks per se, there is no reason you couldn't use the same logic:

3123::1
E000::0 (/3)
2000::0

CIDR notation is used because it is easier to work with, especially when dealing with 128 bit addresses.
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