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The ungleich IPv6 book » History » Version 4

Ahmed Bilal, 06/10/2019 01:22 PM

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h1. The ungleich IPv6 book
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A resource for IPv6 beginners
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h2. Status
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**IN PROGRESS**
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h2. Tools needed
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You would need the following things to follow this Wiki.
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# A Linux Distribution
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# *sipcalc* utility
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h2. Understanding networks, network masks
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Sample IPv6 Address **2001:0db8:85a3:0000:0000:8a2e:0370:7334**
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IPv6 address have a size of 128 bits while IPv4 have a size of 32 bits.
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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).
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h3. Address Compression
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We can compress the IPv6 address. Following are some simple rules
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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:
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    2001:db8:85a3:0:0:8a2e:370:7334
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2. One or more consecutive groups containing zeros only may be replaced with a single empty group, using two consecutive colons (::).[1] 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:
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    2001:db8:85a3::8a2e:370:7334
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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
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h3. Address Ranges
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    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**
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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.
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h3. Cool Tricks with @sipcalc@
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Run the following command on your terminal
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@sipcalc 2a0a:e5c1:100::/40@
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<pre>
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[meow@meow-pc ~]$ sipcalc 2a0a:e5c1:100::/40
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-[ipv6 : 2a0a:e5c1:100::/40] - 0
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[IPV6 INFO]
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Expanded Address	- 2a0a:e5c1:0100:0000:0000:0000:0000:0000
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Compressed address	- 2a0a:e5c1:100::
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Subnet prefix (masked)	- 2a0a:e5c1:100:0:0:0:0:0/40
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Address ID (masked)	- 0:0:0:0:0:0:0:0/40
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Prefix address		- ffff:ffff:ff00:0:0:0:0:0
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Prefix length		- 40
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Address type		- Aggregatable Global Unicast Addresses
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Network range		- 2a0a:e5c1:0100:0000:0000:0000:0000:0000 -
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			  2a0a:e5c1:01ff:ffff:ffff:ffff:ffff:ffff
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</pre>
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If we subtract the network range
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<pre>0x2a0ae5c101ffffffffffffffffffffff - 0x2a0ae5c1010000000000000000000000</pre>
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How many addresses we get? **2^88**. We can also get the same result by 2^(128 - network bits) = 2^(128 - 40) = 2^88.
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Similarly, How many addresses we get if we have **2a0a:e5c1:100::/48** network?
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**Answer:** 2^(128-48) = 2^80. Good.
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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?**
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Run the following command on your terminal
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@sipcalc 2a0a:e5c1:100::/40@
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then
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@sipcalc 2a0a:e5c1:100::/48@
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<pre>
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[meow@meow-pc ~]$ sipcalc 2a0a:e5c1:100::/40
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-[ipv6 : 2a0a:e5c1:100::/40] - 0
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[IPV6 INFO]
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Expanded Address	- 2a0a:e5c1:0100:0000:0000:0000:0000:0000
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Compressed address	- 2a0a:e5c1:100::
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Subnet prefix (masked)	- 2a0a:e5c1:100:0:0:0:0:0/40
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Address ID (masked)	- 0:0:0:0:0:0:0:0/40
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Prefix address		- ffff:ffff:ff00:0:0:0:0:0
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Prefix length		- 40
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Address type		- Aggregatable Global Unicast Addresses
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Network range		- 2a0a:e5c1:0100:0000:0000:0000:0000:0000 -
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			  2a0a:e5c1:01ff:ffff:ffff:ffff:ffff:ffff
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</pre>
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<pre>
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[meow@meow-pc ~]$ sipcalc 2a0a:e5c1:100::/48
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-[ipv6 : 2a0a:e5c1:100::/48] - 0
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[IPV6 INFO]
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Expanded Address	- 2a0a:e5c1:0100:0000:0000:0000:0000:0000
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Compressed address	- 2a0a:e5c1:100::
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Subnet prefix (masked)	- 2a0a:e5c1:100:0:0:0:0:0/48
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Address ID (masked)	- 0:0:0:0:0:0:0:0/48
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Prefix address		- ffff:ffff:ffff:0:0:0:0:0
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Prefix length		- 48
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Address type		- Aggregatable Global Unicast Addresses
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Network range		- 2a0a:e5c1:0100:0000:0000:0000:0000:0000 -
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			  2a0a:e5c1:0100:ffff:ffff:ffff:ffff:ffff
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</pre>
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**Answer:** 2^(48 - 40) = 2^8 = 256. So, you can put 256 /48 networks in /40.
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h2. References
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* https://en.wikipedia.org/wiki/IPv6_address