32. IPv6_Part2

IPv6 Address Configuration (EUI-64)

Extended Unique Identifier (EUI-64) is a method used to convert a 48-bit MAC address into a 64-bit interface identifier. This identifier then becomes the “host portion” of a /64 IPv6 address.

EUI-64 Conversion Example:

1. Given MAC address: 782B CBAC 0867
2. Split and insert FF FE: 782B CBFF FEAC 0867
3. Invert the 7th bit of the first byte (8 becomes A in hex): 7A2B CBFF FEAC 0867

Resulting EUI-64 Interface Identifier: 7A2B CBFF FEAC 0867

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Configuring IPv6 Addresses with EUI-64

When configuring IPv6 addresses using EUI-64, the MAC address undergoes the process outlined above to form the interface identifier. This identifier is then combined with the network prefix to create the full IPv6 address.

• Example: Notice how the “E” in the “2001:DB8…” address changes to “C” due to the 7th bit being flipped (from 1110 to 1100).

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Why Invert the 7th Bit?

MAC addresses are categorized into two types:

1. Universally Administered Address (UAA):
   • Uniquely assigned by the manufacturer.
2. Locally Administered Address (LAA):
   • Manually assigned by an admin or protocol. It doesn’t need to be globally unique.

The 7th bit of the MAC address, known as the Universal/Local (U/L) bit, helps identify whether the MAC address is UAA or LAA:

• U/L bit = 0: UAA
• U/L bit = 1: LAA

In IPv6 EUI-64, this meaning is reversed:

• U/L bit = 0: MAC address is an LAA.
• U/L bit = 1: MAC address is a UAA.

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IPv6 Address Types

1) Global Unicast Addresses

• Public IPv6 addresses that can be used over the internet. They must be registered and globally unique.
• Initially defined within the 2000::/3 block but now includes all addresses not reserved for other purposes.

2) Unique Local Addresses

• Private IPv6 addresses for internal network use. These do not need to be registered or globally unique and cannot be routed over the internet.
• Uses the FC00::/7 block, with the first two digits now required to be FD due to an update.

3) Link-Local Addresses

• Automatically generated on IPv6-enabled interfaces, using the FE80::/10 block. These addresses are confined to a single link (subnet) and are not routable.
• Commonly used for:
  • Routing protocol peerings (e.g., OSPFv3).
  • Next-hop address for static routes.
  • Neighbor Discovery Protocol (NDP).

4) Multicast Addresses

• Multicast allows a single source to send data to multiple destinations in a group. IPv6 uses FF00::/8 for multicast addresses, and unlike IPv4, IPv6 does not use broadcast addresses.
• You must know the multicast addresses for each router type, as IPv6 and IPv4 addresses share the same last digit.

IPv6 Multicast Scope Types:

• Interface-Local (FF01): Packet stays within the local device.
• Link-Local (FF02): Packet remains within the local subnet.
• Site-Local (FF05): Packet can be routed within a single physical location.
• Organization-Local (FF08): Packet can be routed within an entire organization.
• Global (FF0E): Packet can be routed over the internet.

5) Anycast Address

• Anycast is a feature where multiple routers are configured with the same IPv6 address. The routing protocol directs packets to the nearest router configured with that address based on the routing metric.
• Anycast addresses do not have a specific range; instead, a regular unicast address is designated as an anycast address.

Example Command: R1(config-if)# ipv6 address 2000:db8:1:1::99/128 anycast

6) Other IPv6 Addresses

• :: Address: The unspecified IPv6 address, used when a device doesn’t yet know its own address. IPv6 default routes are configured to ::/0 (equivalent to IPv4’s 0.0.0.0).
• ::1 Address: The loopback address, used to test the protocol stack on the local device (equivalent to IPv4’s 127.0.0.1).

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