EUI-64

EUI-64 (Extended Unique Identifier) is a method to automatically configure IPv6 host addresses
1. A MAC address is a /48 address compared to the /64 host portion of the IPv6 address
2. FF:FE is injected in the middle of the /48 MAC address to bring it up to 64 bits
3. Additionally, the 7th bit in the MAC address is inverted
  4. For example, a MAC address starts with FC
  1. FC in binary is 11111100
  2. Flip the 7th bit to 11111110
  3. It is now FE
  5. Example 1
  1. ca01.2f24.0000
  2. 2001:DB8:0:1: C801:2FFF:FE24:0
  6. Example 2
  1. ca01.2f24.0038
  2. 2001:DB8:: C801:2FFF:FE24:38
There are two ways to configure it on an interface
- Manually specifying the network:
  - config-if# ipv6 address <network address> eui-64
- Using NDP to automatically configure the address
  - config-if# ipv6 address autoconfig

EUI-64 Addresses
1. A Cisco router can generate full IPv6 addresses for itself when given the interface and /64 network to use
  2. The host portion of the address is derived from the interface's MAC address, which is guaranteed to be globally unique
  3. A MAC address is a /48 address compared to the /64 host portion of the IPv6 address
  4. FF:FE is injected in the middle of the /48 MAC address to bring it up to 64 bits
  5. Also, the 7th bit is inverted
  1. For example, a MAC address starts with FC
  1. FC in binary is 11111100
  2. Flip the 7th bit to 11111110
  3. It is now FE
2. The router will borrow the MAC address from the first ethernet port for non-Ethernet interfaces such as Serial ports
3. It is best not to use EUI-64 on router interfaces
  1. It is better to use a memorable address such as 2001:db8:0:1::1
  2. EUI-64 is much more useful for use with hosts
Configure EUI-64
5. Config# int f0/0
1. Config-if# ipv6 address 2001:db8:0:1::/64 eui-64
6. Config# int f2/0
1. Config-if# ipv6 address autoconfig
EUI-64 Address Verification
1. # sh int f0/0
  1. ! Hardware is DEC21140, address is ca01.2f24.0000
2. # sh int f2/0
  1. ! Hardware is DEC21140, Address is ca01.2f24.0038
3. # sh ipv6 interface brief
  1. ! FastEthernet 0/0 (up/up)
  2. ! 2001:DB8:0:1:C801:2FFF:FE24:0
  3. ! FastEthernet 2/0 (up/up)
  4. ! 2001:DB8::C801:2FFF:FE24:38

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