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Deploying IPv6 in a Cisco UC Environment – Part 2

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Part two of the series on IPv6 and its impact on the Cisco UC environment.  This post will address some of the basics of how IPv6 hosts are addressed.

IPv6 Address Format

An IPv6 address consists of 8 sets of 16-bit hexadecimal values separated by colons (:), totaling 128 bits in length. For example: 2001:0db8:1234:5678:9abc:def0:1234:5678

Leading zeros can be omitted, and consecutive zeros in contiguous blocks can be represented by a double colon (::). Double colons can appear only once in the address. For example: 2001:0db8:0000:130F:0000:0000:087C:140B

This address can be abbreviated as: 2001:0db8:0:130F::87C:140B

IPv6 unicast addresses generally use 64 bits for the network ID and 64 bits for the host ID.


The network ID is administratively assigned, but the host ID can be auto-configured by any of the following methods:

  • Using a randomly generated number
  • Using DHCPv6
  • Using the Extended Unique Identifier (EUI-64) format, which expands a 48-bit MAC address to 64 bits by inserting FFFE into the middle 16 bits.  This is commonly used for Cisco IP phones, gateways, routers, etc.  In this method, a device with a MAC address 00-90-27-17-FC-0F would have a EUI-64 host ID of 0290:27FF:Fe17:FC0F.

IPv6 Address Types

Unlike IPv4, IPv6 interfaces are expected to have multiple addresses.  The following types of IPv6 addresses can be on an interface:

  • Unicast address: This identifies a single node, exactly like an IPv4 address.
  • Multicast address: This identifies a group of nodes or interfaces, like an IPv4 multicast address. Broadcast address are obsolete in the IPv6 suite.  Multicast addresses are used instead.
  • Anycast address: This identifies a group of nodes or interfaces. Traffic sent to an anycast address will be received by the nearest node in the group. An anycast address is essentially a unicast address assigned to multiple devices multiple devices with a host ID of 0000:0000:0000:0000.

Written by Matthew Berry

March 3rd, 2011 at 1:44 pm

Posted in Blog

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