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:

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:

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:

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:

Nice Examples.

Rene,

Looks like the third example have mistakes. The summary address should be 2001:DB8::/60. can you confirm??

Got it. I have done the same mistake which have mentioned. I have calculated wrongly before reading details.

“Be careful that you don’t accidently convert number 12 from decimal to binary.”

OMG I cannot believe how easy IPV6 is. Granted this is my first time passing through these lessons and if I didn’t recover or think about what I just learned it could easily be forgotten but you really have me looking at it differently.

I like to count backwards from right to left when doing my summaries and one thing about hex that makes it easy is that its in blocks of 4 “0000” so its always “8 4 2 1” those are easy numbers to work with and that part is just simple math but more pattern and grouping really and I love patterns and groupings its how my mind tends to associate and think.

so find the like pattern then count from left to right (that’s your first pattern grouping) then count backwards from right to left and stop just where your pattern ends and blam you have your summary. Now the tricky part was what you mention about making sure to not go from decimal to binary. I did that as well treating the 12 as the first octet. when it was actually a “1” and a “2” but other than being careful with that summarization is easy with IPV6.

who would have thought I would be able to do that when I first started looking at IPV6 for my COMPTIA and even later for my CCENT and then CCNA I was like this is something only some really crazy smart person could get its not ever going to be usable or practicable but now with these lessons something has just clicked into place and I went from that to wow I can do this and really its easy…

Great Lesson!

Glad to hear you like it Max!

It takes time to get used to hex/nibbles. When you just started, it’s easy to forget you are working with hex, not decimal. A common trap is to translate something like 10 (decimal) to 00001010 while it should be 0001 0000 since it’s hexadecimal.

Keep practicing and it will become much easier.