Dhcpv6 Prefix Delegation Example - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BROADBAND ACCESS CONFIGURATION GUIDE 2010-10-12 Configuration Manual

DHCPv6 Prefix Delegation Example

Copyright © 2010, Juniper Networks, Inc.
You can configure a list of up to four domain names in an IPv6 local pool to be used
during the resolution of hostnames to IP addresses. These domain names are returned
to clients in the DHCPv6 responses as part of the Domain Search List option.
You can configure an IPv6 local address pool in an AAA domain map to assign prefixes
to requesting DHCPv6 clients using the ipv6 prefix-pool-name command in Domain
Map Configuration mode. If the authentication server returns the IPv6 local address
pool name in the Framed-IPv6-Pool attribute of the RADIUS-Access-Accept message,
this pool overrides the IPv6 local address pool configured in the domain map.
You cannot delete a pool or a prefix range from which prefixes have been allocated to
requesting routers or DHCPv6 clients. However, you can forcibly delete such a pool or
prefix range by using the force keyword in the ipv6 local pool poolName and prefix
commands. If a pool is deleted or the prefix range associated with the pool is deleted,
and prefixes have been assigned to DHCPv6 clients or requesting routers, the
corresponding DHCPv6 bindings are also deleted.
When multiple prefix ranges are configured in a pool, the DHCPv6 prefix delegation
feature allocates prefixes from the configured ranges in the order of the assigned prefix
length. The delegating router or the DHCv6 server attempts to allocate a prefix from
the range with lowest assigned prefix length. If this attempt fails because the pool has
been fully allocated, the server tries to allocate 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.
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.
Chapter 1: Configuring Remote Access
103