IPv6 Prefix Allocation Using Neighbor Discovery Router Advertisements from IPv6 Address Pools Overview

You can configure IPv6 local address pools for Neighbor Discovery router advertisements on a virtual router in order to allocate prefixes to Neighbor Discovery clients. These pools can be used to assign prefixes from the E Series router.

An IPv6 local address pool for Neighbor Discovery router advertisements is configured on the router running the B-RAS application, which contains information about the prefixes. When the B-RAS application running on the E Series router receives a request from a PPP IPv6 client, it selects an available prefix and allocates it to the client.

Allocation of Neighbor Discovery Prefixes for IPv6 Subscribers over PPP Links

When a PPP user establishes a PPP connection with the E Series router functioning as a remote access server, the subscriber is first authenticated using the RADIUS protocol. The Access-Accept message returned from the RADIUS server can contain different IPv6 attributes, including the IPv6-NdRa-Pool attribute, which contains the name of the IPv6 pool from which a prefix needs to be assigned to the subscriber. The prefix is assigned to the subscriber using the Neighbor Discovery router advertisements feature.

Order of Preference in Determining the Local Address Pool for Allocating Prefixes for Neighbor Discovery Router Advertisements

You can configure multiple local address pools for Neighbor Discovery router advertisements on a virtual router. When multiple pools are configured, the pool that is used to allocate the prefix to the requesting PPPv6 subscriber is selected using the following order of preference:

  1. If the aaa dhcpv6-ndra-pool override command is not configured and a pool name is returned by the RADIUS server in the IPv6-Ndra-Pool attribute, that pool is used to allocate the prefix to the client.
  2. If the aaa dhcpv6-ndra-pool override command is configured and a pool name is returned by the RADIUS server in the Framed-Ipv6-Pool attribute, that pool is used to allocate the prefix to the client.
  3. If the RADIUS server does not return a pool name in either of the above-mentioned points, based on the aaa dhcpv6-ndra-pool override command, the pool name configured in the AAA domain map is used.

Order of Preference in Assigning Prefixes when Neighbor Discovery Router Advertisements are Configured on an Interface

The router running the B-RAS application uses the following order of preference to determine the source from which the Neighbor Discovery router advertisements prefix is allocated to the requesting PPPv6 subscriber from the Neighbor Discovery Router Advertisements server:

  1. An interface that is configured for the Neighbor Discovery router advertisements prefix is given priority over the RADIUS attributes returned in the Access-Accept message or the prefixes configured in the IPv6 local address pool for Neighbor Discovery router advertisements on the router running the B-RAS application.
  2. The RADIUS server might return one or more of the following attributes in the Access-Accept message in response to the client authentication request:
    • Ipv6-NdRa-Prefix (VSA 26-129)
    • Framed-IPv6-Prefix (RADIUS IETF attribute 97)
    • Framed-IPv6-Pool (RADIUS IETF attribute 100)
    • IPv6-Ndra-Pool (VSA 26-157)

    If either of the first two attributes are returned, then the prefix contained in those attributes is used, and the pool name in the Framed-IPv6-Pool or Ipv6-Ndra-Pool attribute is ignored.

  3. If the RADIUS server does not return any of the above-mentioned attributes, the IPv6 prefix pool name of the Neighbor Discovery router advertisements mentioned in the AAA domain map will be used to allocate the prefix to the requesting PPPv6 subscriber.

Guidelines for Allocating Neighbor Discovery Prefixes Using IPv6 Address Pools

The following are guidelines for allocating prefixes using IPv6 address pools for Neighbor Discovery router advertisements:

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