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# The ungleich IPv6 book¶

A resource for IPv6 beginners

IN PROGRESS

## Tools needed¶

You would need the following things to follow this Wiki.
1. A Linux Distribution
2. sipcalc utility

IPv6 address have a size of 128 bits while IPv4 have a size of 32 bits.

IPv6 address is divided into 8 groups each made up of 4 hexadecimal digits. (Each hexadecimal digit takes 1 nibble or 4 bits). So, each group takes 2 bytes (16 bits).

We can compress the IPv6 address. Following are some simple rules

1. Leading zeroes in a group may be omitted, but each group must retain at least one hexadecimal digit. Thus, the example address 2001:0db8:85a3:0000:0000:8a2e:0370:7334 can be written as:

``2001:db8:85a3:0:0:8a2e:370:7334``

2. One or more consecutive groups containing zeros only may be replaced with a single empty group, using two consecutive colons (::). The substitution may only be applied once in the address, however, because multiple occurrences would create an ambiguous representation. Thus, the example address 2001:0db8:85a3:0000:0000:8a2e:0370:7334 can be further simplified:

``2001:db8:85a3::8a2e:370:7334``

The localhost (loopback) address, 0:0:0:0:0:0:0:1, and the IPv6 unspecified address, 0:0:0:0:0:0:0:0, are reduced to ::1 and ::, respective

``Just to check we are on same page. What is the expanded form of 2a0a:e5c1:100::/48? Answer: 2a0a:e5c1:100:0:0:0:0:0``

The size of a block of addresses is specified by writing a slash (/) followed by a number in decimal whose value is the length of the network prefix in bits. For example, an address block with 48 bits in the prefix is indicated by /48. Such a block contains 2^(128 − 48) = 2^80 addresses. The smaller the value of the network prefix, the larger the block.

### Cool Tricks with `sipcalc`¶

Run the following command on your terminal

`sipcalc 2a0a:e5c1:100::/40`

```[meow@meow-pc ~]\$ sipcalc 2a0a:e5c1:100::/40
-[ipv6 : 2a0a:e5c1:100::/40] - 0

[IPV6 INFO]
Prefix length        - 40
Network range        - 2a0a:e5c1:0100:0000:0000:0000:0000:0000 -
2a0a:e5c1:01ff:ffff:ffff:ffff:ffff:ffff
```

If we subtract the network range

`0x2a0ae5c101ffffffffffffffffffffff - 0x2a0ae5c1010000000000000000000000`

How many addresses we get? 2^88. We can also get the same result by 2^(128 - network bits) = 2^(128 - 40) = 2^88.

Similarly, How many addresses we get if we have 2a0a:e5c1:100::/48 network?

Now, let me ask you a slightly different question. How many 2a0a:e5c1:100::/48 networks can we fit into 2a0a:e5c1:100::/40 network?

Run the following command on your terminal

`sipcalc 2a0a:e5c1:100::/40`
then
`sipcalc 2a0a:e5c1:100::/48`

```[meow@meow-pc ~]\$ sipcalc 2a0a:e5c1:100::/40
-[ipv6 : 2a0a:e5c1:100::/40] - 0

[IPV6 INFO]
Prefix length        - 40
Network range        - 2a0a:e5c1:0100:0000:0000:0000:0000:0000 -
2a0a:e5c1:01ff:ffff:ffff:ffff:ffff:ffff
```
```[meow@meow-pc ~]\$ sipcalc 2a0a:e5c1:100::/48
-[ipv6 : 2a0a:e5c1:100::/48] - 0

[IPV6 INFO]