IPv6 Icky EUI-64 Drill 1

certskills
By certskills April 1, 2017 08:50

This post starts a new type of review post for #ICND2 or #CCNA: the icky EUI-64 drill. It’s icky for two reasons: it requires you to think in binary, and it rhymes. The goal: Starting with a MAC address and a /64 IPv6 prefix, predict the IPv6 address the host would use if using IPv6 Stateless Auto Address Configuration (SLAAC).

Today’s post lists sample problems; the follow-up post will show the answers.

Related links: Deeper info from the ICND2 OCG book

The EUI-64 Rules

The EUI-64 process to derive an IPv6 address begins with two facts, followed by a process that uses those facts. The facts:

  • A 64-bit IPv6 prefix (typically learned from a router)
  • The host’s MAC address

Using these two facts, the process to form the full 128-bit IPv6 unicast address is pretty simple. First, you use the learned prefix as the first 64 bits. Simple enough. However, then you have to convert the first byte, or at least the 2nd hex digit, to binary and back. EUI-64 rules used by SLAAC tell you how to make the last 64 bits, as follows:

  1. Split the MAC into two halves, each 6 hex digits digits / 3 bytes / 24 bits long.
  2. Insert hex FFFE in the middle between the two, completing the 16 hex digits in the 2nd half of the number
  3. Do some math on the first byte of the MAC address to invert (flip) the 7th of 8 bits (counting left-to-right)

Figure 1 summarizes the ideas.

Figure 1: EUI-64 Rules Used by SLAAC

For this exercise, take the listed prefixes and MAC addresses, and create the IPv6 address the device would use.

Extra credit: Also, if interested, you can think about the solicited node multicast address the host would use along with the unicast address. This multicast address is formed by taking the unicast address, and replacing the first 104 bits (26 hex digits) with FF02::1:FF00::/104. In other words, use the solicited node multicast prefix with those last 6 hex digits of the unicast IPv6 address.

Problems to Do

The following Table shows five prefixes and MAC unabbreviated IPv6 addresses; convert these to the shortest possible abbreviated IPv6 address

Table 1:

 

 

EIGRP Enabler #3 - Answers
IPv6 Icky EUI-64 Drill 1 - Answers
certskills
By certskills April 1, 2017 08:50
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1 Comment

  1. packetx August 6, 03:45

    Great practice thanks !

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