Version 6.8 125 Mediant MSBR
Configuration Guide 20. IPv6 Routing
20.5 DCHPv6
DHCPv6 is the DHCP protocol that runs with IPv6. This protocol works in a different way
on IPv6 than on IPv4; however, the goal of the protocol remains the same.
The MSBR can obtain configuration if it's WAN interface using two modes: stateful or
stateless. In stateful mode, the entire configuration is provided using the DHCP server. In
stateless mode, the IP configuration can be provided using the Network Discovery Protocol
(NDP), and other configuration protocols such as NTP. In addition, a DNS address can be
provided using the DHCP server, and also the NDP protocol can be used. In both cases,
the hosts cannot obtain an IP address using Prefix Delegation. If the WAN address is
dynamically configured, the hosts can obtain dynamic IP addresses using Router
Advertisement (RA) or it can be configured as a static address.
Some routers connected to ISPs require IPv6 addresses not only for their WAN interfaces,
but also for hosts connected to their LAN interfaces. In the IPv4 world, the ISP provides the
router with one or more IP addresses for the WAN interface. The network operator uses
NAT with a local DHCP server to assign IP addresses to the hosts on the LAN side.
However, in the IPv6 world, there is no NAT protocol because there is no need to save
IPv6 addresses - they are abundant. In the IPv6 world, the IPv6 addresses are provided by
the ISP using prefix delegation. Prefix delegation, described in RFC 3769, is used to assign
a router IP prefix which can be delegated to the LAN side as networks. Hosts will receive
IPv6 addresses in these networks.
Figure 20-6: IPv6 Prefix Delegation
The figure above shows an example of a network topology using the IPv6 prefix delegation.
The ISP router delegates the prefix 2001:0100:0:FFF0::/56 to the MSBR. The MSBR needs
to assign addresses to three LAN networks: Interface VLAN 10, Interface VLAN 20 and
Interface VLAN 30. Every host on the LAN network is assigned with an address with prefix
/64. This means that the MSBR can assign every LAN interface with a network in an
amount of 2
64−56
= 2
8
= 256 . This means that MSBR can assign addresses on 256
VLANs. The computers attached to interface VLAN 1 will have IPs in the network
2001:100:0:FF00:: /64, on VLAN 2, the computers will have IPs in the network
2001:100:0:FF01:: /64 etc.
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