1.11 IPv6 Address Types

CCNP RS 300-101, Describing Routing Protocols, Uncategorized

There are several IPv6 address types to know.

Aggregatable Global Address – these are addresses assigned for internet use; they are assigned to RIRs for distribution to organizations. They have the following characteristics.

  • Contain a Global Routing Prefix, Subnet ID (SLA), and an Interface ID assigned to a service provider, organization/site, and host, respectively
  • Global Addresses begin with a binary value of 001 (2000::/3); this provides an effective range from 2000::0 to E000::0
  • Global addresses are required to have a 64-bit host identifier
  • The 2001:DB8::/32 address space is reserved
Global Address breakdown.

Link-Local Address – these are unicast addresses that are typically auto-configured on a device interface. They are used for local operations and are not globally routable. They have the following characteristics.

  • Used only locally, for neighbor discovery protocol and stateless auto-configuration purposes
  • Nodes on a local link can use link-local addresses to communicate with each other
  • Link-local addresses begin with a binary value of 1111 1110 10 (FE80::/10) and use a 64-bit interface ID (EUI-64) with 54 bits of “zeros” in-between.
  • These addresses are automatically generated when IPv6 is enabled on a Cisco router interface; they do not require manual configuration or DHCP as in IPv4 because of EUI-64, which uses the 48-bit MAC address of the interface to dynamically create the address.

To create an EUI-64 address, follow these steps:

  • Split the 48-bit MAC address into its OUI (24-bits) and NIC (24-bits)
  • Insert “FF FE” between the OUI and NIC portions of the MAC
  • Convert the first two hexadecimal characters into binary, and flip the 7th bit
  • You now have the EUI-64 portion of the link-local address
Link-Local Address breakdown.

Unique-Local Address – These are uniquely assigned address but are not routable on the internet. They are intended to be used for communications within or between local sites. They are therefore the equivalent to RFC1918 private IPv4 addresses. They have the following characteristics.

  • They begin with the prefix FC00::/7
  • The /7 address space is split into FC00::/8 and FD00::/8 ranges, with the upper half identified for use (so you’ll likely only be able to use addresses in the FD00::/8 range)
Unique-Local Address breakdown.

Other IPv6 Address types to know:

  • Loopback (::1/128) – for loopback addressing destined to the sending device
  • Unspecified (::/128) – when no address has been assigned and a device requests to have one configured for it
  • Default Route (::/0) – the syntax for a default route
  • IPv4 Compatible (::A.B.C.D) – a way to convert IPv4 to IPv6 by turning it to hex
  • Multicast (FF00::/8) – for use in multicast. These are very common because there are no broadcast addresses in IPv6.
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