Overview

This chapter covers IPv6 unicast connectivity within an enterprise or service provider network, and discusses available options, implementation scenarios, and deployment recommendations. The intent is to present this information as it applies to different parts of the network:

• Hosts or Customer Edge (CE) routers

• Access and backbone infrastructures

The concepts that are relevant in making a host operational in an IPv6 network are presented first. This section of the chapter reviews the mechanisms for providing hosts and CE routers with an IPv6 address, and introduces new concept such as prefix delegation, for providing name-resolution support and for some AAA (authentication, authorization and accounting) management.

Subsequent sections discuss the delivery of IPv6 unicast connectivity from a network perspective. The service deployment will most likely interact at some point with or over some segments with existing IPv4 infrastructures. In this interaction, there are three deployment approaches:

• IPv6 only IPv6 is the only protocol running over a given link (physical or virtual).

• Dual stack IPv4 and IPv6 run together over the same link (physical or virtual).

• IPv6 at the edge only IPv6 is confined to sites located at the edges of an existing IPv4 core infrastructure that it has to traverse.

These three approaches define a framework for the service deployment strategy. The technological means to implement them are presented in the context of the two relevant layers of the network: access and backbone.

Table 3-1 summarizes the deployment mechanisms presented in this chapter. Along with the scope and significant features, the table lists the areas of the network where the mechanism would fit best.

Table 3-1. IPv6 Unicast Deployment Mechanisms

Mechanism		Scope	Where Used	Key Features	Limitations
Native IPv6	Routed	Host/Inter-site	Access/Backbone	Simplest method in terms of setup.	Support on all network elements in the path.
	Bridged (IPv6 RBE)	Host	Access	IPv6 RBE routes the IPv6 traffic out of a bridged ATM encapsulation.
	PPP	Host/Inter-site	Access
IPv6 over MPLS	Dedicated links/circuit	Inter-site	Backbone	It is a native method where a physical or virtual link interconnects two sites.
	6PE	Inter-site	Backbone	MPLS infrastructure. IPv4 Label Switch Path setup. IPv6 transport over MPLS.	Applicable to MPLS infrastructure only. IPv4 and IPv6 traffic follow the same paths.
	IPv6 MPLS	Inter-site	Backbone	MPLS infrastructure. Native IPv6 Label Switch Path setup. IPv6 transport over MPLS	MPLS only. LDP and RSVP IPv6 implementation not available.
Tunnels	Configured	Host/Inter-site	Access/Backbone	Static, supported by most IPv6 implementations. Tunnel endpoints can be secured with IPv4 IPsec.	Management overhead.
	Tunnel broker and tunnel server	Host	Access	Provides the means to automatically set up configured tunnels upon request. A dedicated device or a router performs this function.	Potential security implications.
	Teredo	Host	Access	Works through multiple NATs.	Management overhead.
	GRE	Inter-site	Access/Backbone	Static. It supports the transport of layer 2 multicast, which is important for the control plane of some protocols (IS-IS).	Management overhead.
	ISATAP	Host/Inter-site	Access/Backbone	Automatic tunnel.	Performance. No solution for multicast.
	6 to 4	Inter-site	Access/Backbone	Automatic tunnel. Reserved address space 2002::/16.	Return path selection not optimized. Security issue if not secured through IPsec.

These mechanisms are presented in this chapter along with more in-depth discussions on deployment recommendations. The recommendations are made only from the perspective of providing IPv6 unicast connectivity. Other selection criteria are presented in the chapters dedicated to other services, such as multicast, virtual private networking (VPN), quality of service (QoS), and security.

Overall, a deployment strategy choice depends on technical considerations (best way to leverage existent IPv4 infrastructure and to circumvent constraints such as Network Address Translation [NAT], for example) as well as cost-effectiveness considerations (for instance, return on the investment of upgrading existent resources or adding new ones). Nevertheless, when possible, it is recommended to begin with native IPv6no IPv6 tunnelsbecause this represents the ultimate goal of the IPv6 integration.