Juniper JUNOSE 11.0.X MULTICAST ROUTING, Configuration Manual

Page: 143 / 788

a prefix from the subsequent prefix ranges. These ranges could have the same
prefix length as the first one or a higher length.
NOTE: Although you can configure an IPv6 local pool with the assigned prefix length
as /128, which implies a full IPv6 address, this assignment is not useful for the
DHCPv6 prefix delegation feature because it assigns a prefix with a length of only
/64 or less. A pool with an assigned prefix length of /128 is useful when complete
IPv6 addresses are assigned to the DHCPv6 clients.
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 Framed-IPv6-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 DHCPv6 prefix delegation feature,
which is covered in the next section.
DHCPv6 Prefix Delegation Example
Consider a scenario in which a number of devices on a home network are connected
to a customer premises equipment, CPE1, which is the requesting router. CPE1 is
connected using a PPP link to the provider edge device, PE1, which is an E Series
router operating as the DHCPv6 server or delegating router. After the IPv6 link is
formed between CPE1 and PE1 and the IPv6 link-local address is created, CPE1
requests and obtains prefixes that are shorter than /64 (usually of length, /48) from
PE1.
CPE1 is connected to the home network. CPE1 divides the single delegated prefix
that it received from PE1 into multiple /64 prefixes and assigns one /64 prefix to
each of the links in the home network. The address allocation mechanism in the
subscriber network can be performed using ICMPv6 neighbor discovery in router
advertisements, DHCPv6, or a combination of these two methods.
When PE1 receives a request for prefix delegation from CPE1, PE1 assigns prefixes
from the list of unallocated prefixes in the IPv6 local pool.
Order of Preference in Determining the Local Address Pool for Allocating Prefixes
You can configure multiple local address pools on a virtual router. When multiple
pools are configured, the pool that is used to allocate the prefix to the requesting
router is selected using the following order of preference: If a pool name is returned
by the RADIUS server in the Framed-IPv6-Pool attribute, that pool is used to delegate
the prefix to the client.
■
If the RADIUS server does not return a pool name in the Framed-IPv6-Pool
attribute, the pool name configured in the AAA domain map is used.
■
If no local address pool name is configured in the AAA domain map, the IPv6
address of the interface on which the request was received is used to determine
the pool.
DHCPv6 Local Address Pools for Allocation of IPv6 Prefixes Overview
■ 103
Chapter 1: Configuring Remote Access