I need help understanding prefixes on ipv6 like /64 /56 and subnet part.

[dolanduck.]

I'm having trouble understanding the prefix part.

from what i know for example  2001:dead:beef::/48 is my network prefix i cant change those 48 bits.

and that my next 16 hex bits 0000 is my sub net bits when you add them up give you 64 bits.

but whats confusing me if  you have a /56 does that mean you ignore the the the first 8 bits ? 

0000

and i heard from other people you can sub-net from there with a /56

0100

0200

and i saw another video where this lady 

she has a ipv6 address of 2000:acdc:1234:6600::/56

and started sub netting

6600

6601

and so on

I'm really confused.

[Seb Rupik]

Hi there,
In your first example, 0100 and 0200, those would be different /56 prefixes:

2001:dead:beef:01::/56
2001:dead:beef:02::/56

Your second example is the correct understanding of IPv6 subnetting.

2001:dead:beef:6601::/64
2001:dead:beef:6602::/64

...are both subnets which are part of the same prefix:

2001:dead:beef:66::/56

cheers,
Seb.

[dolanduck.]

what do you mean different /56 prefix

because this is what the guy told me

"No, since only the first eight bits in that hextet are part of the prefix. That means in this case: 2001:DEAD:BEEF:ABCD::/56 A and B are part of your network portion, while C and D are part of your host portion. So counting up subnets for a /56 scheme starts at 2001:DEAD:BEEF:01 | 00:0000:0000:0000:0000, since everything behind the | is not part of your „prefix mask“

thats what got me confused

[Seb Rupik]

hmmmm, that quote has some incorrect elements.

AB are part of the prefix, CD make up the subnet ID. The host (or interface) ID starts after the 64th bit.

So a prefix of 2001:DEAD:BEEF:AB::/56 will give a subnet range of:

2001:DEAD:BEEF:AB00::/64   to  2001:DEAD:BEEF:ABFF:/64

Back to original example:

2001:dead:beef:01::/56
2001:dead:beef:02::/56

The first prefix has the range 2001:dead:beef:0100::/64 to 2001:dead:beef:01ff::/64  . When you increment the final subnet ID by one, you will be in the next /56

2001:dead:beef:02::/56

If in any doubt have a play with an online subnet calculator:

http://www.gestioip.net/cgi-bin/subnet_calculator.cgi

cheers,

Seb.

[mlund · Accepted solution]

Hi
You can subnet the same way as in ipv4. Just take bits in order from left to right.
If you got the prefix 2001:dead:beaf:ab00::/56 from your provider. You can subnet it in different way.
First, You can't touch the first 56 bits 2001:dead:beaf:ab so you have start from bits 57 and forward.
you can take one bit and that gives you
2001:dead:beaf:ab00::/57
2001:dead:beaf:ab80::/57

If you take two bits then you have

 2001:dead:beaf:ab00::/58
 2001:dead:beaf:ab40::/58
 2001:dead:beaf:ab80::/58
 2001:dead:beaf:abc0::/58

with three bits it will be
  2001:dead:beaf:ab00::/59
  2001:dead:beaf:ab20::/59
  2001:dead:beaf:ab40::/59
  2001:dead:beaf:ab60::/59
  2001:dead:beaf:ab80::/59
  2001:dead:beaf:aba0::/59
  2001:dead:beaf:abc0::/59
  2001:dead:beaf:abe0::/59
with four bits it will be

 2001:dead:beaf:ab00::/60
 2001:dead:beaf:ab10::/60
 2001:dead:beaf:ab20::/60
 2001:dead:beaf:ab30::/60
and so on until
 2001:dead:beaf:abf0::/60

Be aware though, if you type
 2001:dead:beaf:ab::/56 this is not the same as 2001:dead:beaf:ab00::/56 because 2001:dead:beaf:ab::/56 is actually the same as 2001:dead:beaf:00ab::/56. You can only omit leading zeroes not trailing.

/Mikael

[dolanduck.]

so for the /57 the goes from 0 to 7 = 8

and net next sub-net is 8 to f  =8

and another question i can use 0 right unlike ipv4 ?

[mlund]

Yes, you are correct.

and yes, you can use 0

/Mikael

[Giovanni Alexander Molina]

Lets see it this way you have a /48
/48 + 4 bits that conform an Hex value: BIN (0000 - 1111) = HEX(0 - F) where F is the max value. so you can subnet counting on by 4 by 4 bits.
/56
/60
/64