IPv6 Summarization Example

Summarizing IPv6 prefixes is similar to IPv4 summarization, the big difference is that IPv6 uses 128 bit addresses compared to 32 bits for IPv4 and IPv6 uses hexadecimal addresses.

In this lesson, I’ll explain how to create IPv6 summaries and we’ll walk through some examples together.

Example 1

Let’s start with a simple example:

  • 2001:DB8:1234:ABA2::/64
  • 2001:DB8:1234:ABC3::/64

Let’s say we have to create a summary that includes the two prefixes above. Each hextet represents 16 bits. The first three hextets are the same (2001:DB8:1234) so we have 16 + 16 + 16 = 48 bits that are the same so far. To find the other bits that are the same we only have to focus on the last hextet:

  • ABA2
  • ABC3

We’ll have to convert these from hexadecimal to binary to see how many bits are the same:

ABA2 1010101110100010
ABC3 1010101111000011

I highlighted the bits in red that are the same, the first 9 bits. The remaining blue bits are different. To get our summary address, we have to zero out the blue bits:

AB80 1010101110000000

When we calculate this from binary back to hexadecimal we get AB80. The first three hextets are the same and in the 4th octet we have 9 bits that are the same. 48 + 9 = 57 bits. Our summary address will be:

2001:DB8:1234:AB80::/57

That’s how you can create a summary address for IPv6.

Example 2

This time we have the following 3 prefixes:

  • 2001:DB8:0:1::/64
  • 2001:DB8:0:2::/64
  • 2001:DB8:0:3::/64

And our goal is to create the most optimal summary address. The first three hextets are the same so that’s 16 + 16 + 16 = 48 bits that these prefixes have in common. For the remaining bits, we’ll have to look at the 4th hextet in binary:

0001 0000000000000001
0002 0000000000000010
0003 0000000000000011

Keep in mind that each hextet represents 16 bits. The first 14 bits are the same, to get the summary address we have to zero out the blue bits:

0000 0000000000000000

When we calculate this from binary back to hexadecimal we get 0000. The first three hextets are the same and in the 4th octet we have 14 bits that are the same. 48 + 14 = 62 bits. Our summary address will be:

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Forum Replies

  1. Hi Rene , I don’t understand how you convert nibbles binary to decimal,

  2. Chaps,
    I’ve been writing out the place value systems for binary, decimal and hexadecimal and have spotted a pattern that I can’t explain.

    For instance…

    In Binary - 2 ^ 3 = 1000
    In Decimal - 10 ^ 3 = 1,000
    In Hexadecimal - 16 ^ 3 = 1000

    All results are 1000 even though this is expressed in the three different number systems so are different values.

    The pattern repeats no matter what the next power of is:

    In Binary - 2 ^ 7 = 10000000
    In Decimal - 10 ^ 7 = 10,000,000
    In Hexadecimal - 16 ^ 7 = 10000000

    This is more of an observation that a question I suppose but if

    ... Continue reading in our forum

  3. Hi Gareth

    I think you meant any number ^0 is always 1, right? Any number ^1 is simply itself. But it is quite interesting, this world of mathematics isn’t it!?!?!

    Laz

  4. :slight_smile: Yep - any number to the ^0 is 1 - my bad!!!

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