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How NDRA Works in a Subscriber Access Network
Before NDRA can provide IPv6 address information to the CPE, you need to first obtain a link-local address for the CPE WAN link. NDRA provides address assignment in two phases:
- Link-local address assignment for local connectivity to the BNG
- Global address assignment for global connectivity
The process is as follows:
- During IPv6CP negotiation to establish the PPPoE link between the BNG and the CPE, an interface identifier is negotiated for the CPE.
- The CPE creates a link-local address by appending the
interface identifier with the IPv6 link-local prefix (FE80::/10).
Note: When the interface ID is 0, such as for Windows 7 clients, PPP uses the subscriber’s session ID in place of the interface ID.
The CPE now has IPv6 connectivity to the BNG, and it can use NDRA to obtain its global IPv6 address.
- The CPE sends a router solicitation message to the BNG.
- The BNG responds with a router advertisement message that
includes an IPv6 prefix with a length of /64.
This prefix can come directly from a local NDRA address pool configured on the BNG.
If you are using AAA, a RADIUS server can specify the prefix in the Framed-Ipv6-Prefix attribute, or it can specify an NDRA pool on the BNG from which the prefix is assigned in the Framed-Ipv6-Pool attribute.
- When the CPE receives the 64-bit prefix, it appends its interface ID to the supplied prefix to form a globally routable 128-bit address.
- The CPE verifies that the global address is unique by sending a neighbor solicitation message destined to the new address. If there is a reply, the address is a duplicate. The process stops and requires operator intervention.
