Designs for IPv6 Addressing in a Subscriber Access Network

In some networks, you do not need to assign a global IPv6 address on the CPE WAN link. Your decision depends on the type of CPE being used:

• If the CPE is purchased by the subscriber, and is not a device specifically recommended by the service provider, you need to assign a global IPv6 address that can be routed on the Internet.

• If the CPE is supplied by or recommended by the service provider, you can use the loopback interface to manage the CPE.

  In this case, you can use a link-local address or you can use an address that is derived from DHCPv6 prefix delegation.

To assign a global IPv6 address to the WAN link of the CPE device, you can choose one of the methods described in Table 1.

DHCPv6 prefix delegation automates the delegation of IPv6 prefixes to the CPE. The CPE can then use these prefixes to assign global IPv6 addresses for use in a subscriber LAN. DHCPv6 prefix delegation is useful when the delegating router (the BNG) does not have information about the topology of the networks in which the requesting router (the CPE) is located. In such cases, the delegating router requires only the identity of the requesting router to choose a prefix for delegation.

You can set up the BNG to select IPv6 prefixes through one of the following methods:

• An external source such as a AAA RADIUS server or a DHCP server using the DHCPv6 relay agent.

• Dynamic assignment from a local pool of global IPv6 addresses or prefixes that is configured on the BNG

• Using a AAA RADIUS Server to Obtain Global IPv6 Addresses and IPv6 Prefixes
• Using a Local Pool to Assign IPv6 Addresses or Prefixes

This design (Figure 1) uses DHCPv6 IA_NA and DHCPv6 prefix delegation in your subscriber access network as follows:

• DHCPv6 IA_NA is used to assign a global IPv6 address on the WAN link. The address can come from a local pool or AAA RADIUS.

• DHCPv6 prefix delegation is used for host device addressing. The delegated prefix can come from a local pool or from AAA RADIUS. The CPE uses the delegated prefix for subscriber addressing. The CPE can use NDRA or DHCPv6 to allocate IPv6 addresses on the LAN.

Figure 1: Subscriber Access Network with DHCPv6 IA_NA and DHCPv6 Prefix Delegation

This design (Figure 2) uses NDRA and DHCPv6 prefix delegation in your subscriber access network as follows:

• NDRA addressing is used to provision a global IPv6 address on the WAN link. IPv6 prefixes for NDRA come from a local pool or AAA RADIUS.

• DHCPv6 prefix delegation is used for host device addressing. The delegated prefix can come from a local pool or from AAA RADIUS. The CPE uses the delegated prefix for subscriber addressing. The CPE can use NDRA or DHCPv6 to allocate IPv6 addresses on the LAN.

Figure 2: Subscriber Access Network with NDRA and DHCPv6 Prefix Delegation

If you have a network with a combination of subscriber LANs and single PCs, you can use a combination of design 2 and design 3.

In this design (Figure 3), NDRA is used for addressing a global IPv6 on the WAN link with prefixes from a local pool or AAA RADIUS. The PC does not need a delegated prefix.

Figure 3: Subscriber Access Network with NDRA

If you have a network with a combination of subscriber LANs and single PCs, you can use a combination of Design 2 and Design 3.

In this design (Figure 4), the CPE is a model that is sold by or specified by the service provider. The CPE uses an unnumbered WAN interface. The BNG delegates an IPv6 prefix to the CPE with DHCPv6 prefix delegation. The CPE uses the delegated prefix for subscriber addressing. It can use NDRA or DHCPv6 to allocate the IPv6 addresses on the LAN.

Figure 4: Subscriber Access Network with DHCPv6 Prefix Delegation