Configuration of Global IPv6 Unicast Addresses

We have already discussed the Global IPv6 Address representation and structure. The Internet Assigned Numbers Authority (IANA) and The Internet Committee for Assigned Names and Numbers (ICANN) allocates Global IPv6 address blocks to the five Regional Internet Registries (RIRs). Only global unicast addresses with the first three bits of 001 or 2000::/3 assigned to various Internet address registries. This is a very small portion of available Global IPv6 addresses. A global IPv6 unicast address has three parts which have illustrated in the figure below:-

  • Global routing prefix
  • Subnet ID
  • Interface ID

This is the network portion of the global IPv6 address, which has assigned by the provider. RIRs assign a /48 global routing prefix to customers as shown in the figure. This can use everyone from business networks to individual households. The figure illustrates the structure of a global unicast address using a /48 global routing prefix with 16-bit subnet ID. The range of global IPv6 prefix in the first hextet is 0010 0000 0000 (2000) to 0011 1111 1111 (3FFF).

Static Configuration of Global IPv6 Address on Router

The configuration commands in the Cisco routers are similar for both IPv4 and IPv6. The difference between both is the use of ipv6 in place of IP within the commands. The command is used to configure an IPv6 global unicast address on any interface is “ipv6 address ipv6-address/prefix-length“ For example, Configuration of IPv6 address on Cisco Router interface fa0/0 and fa0/1.

 Router>enable
Router#configure terminal
Router(config)interface fa/0/0
Router(config-if)#ipv6 address 2001:DA1:B111::ABCD:BCD:1 /64
Router(config-if)no shutdown
Router(config-if)exit
Router(config)interface fa/0/1
Router(config-if)#ipv6 address 2001:DA1:B112::ABCD:BCD:1/64
Router(config-if)no shutdown
Router(config-if)exit
Router(config) do wr
Building configuration…
[OK]

Static Configuration of Global IPv6 Address on Host

Similarly, we can configure IPv6 address on a host computer like IPv4 address. For example, As shown in Figure, the IP address configured for the host is 2001: DA1: B111:: ABCD: BCD: 1 and the default gateway address is 2001: DA1: B111:: ABCD: BCD: 1. Both addresses are global unicast addresses. Link-local address of the router can also be configured as the default gateway for the host. Both configurations will work. Static address configuration for the host is best practice in the small network but for a larger network, dynamic assignment of IPv6 addresses configuration is best.

Global IPv6

There are two ways in we can use for dynamic IPv6 address configuration on host computers. The ways to configure IPv6 global unicast address automatically is Stateless Address Auto-Configuration (SLAAC) as well as Dynamic Host Configuration Protocol version 6 (DHCPv6). Using DHCPv6 or SLAAC, the local router’s link-local address will also automatically be specified as the default gateway address for the host.

Stateless Address Auto-Configuration (SLAAC)

It is the unique feature for IPv6 addresses which is not available in IPv4. Using SLAAC, the device can get IPv6 address prefix, prefix length, default gateway address, and other information from an IPv6 router without the use of a DHCPv6 server. All Cisco devices have the capability of the SLAAC but, by default, SLAAC does not provide anything to the client outside of an IPv6 address and a default gateway. Using SLAAC, devices also rely on the local router’s ICMPv6 Router Advertisement (RA) messages to obtain the necessary information.

IPv6 enabled routers to send out ICMPv6 RA messages after every 200 seconds, to all IPv6-enabled devices on the network. RA messages have three option to get an IPv6 address automatically. An RA message will also be sent in response to a host sending an Internet Control Messaging Protocol version 6 (ICMPv6) Router Solicitation (RS) message.  IPv6 routing is not enabled by default.  We can enable IPv6 routing using the following commands.

Router>enable
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#ipv6 unicast-routing
Router(config)# do wr
Building configuration…
[OK]