Mobile Internet basics: Mobile IPv6 in Practice

In this series of six articles, the authors of “Building the Mobile Internet“ provide a tutorial on
extending Internet connectivity into mobile networking by using extensions of
protocols such as IPv4 and IPv6 as well as mobile specific protocols such as
DSMIP, IKEv2 and MoBIKE. Part 5: Mobile IPv6 in practice.

Mobile IPv6 is well documented in the IETF, but it has yet to reach significant deployment because the majority of the Internet is still IPv4 based. Mobile IPv6 is standardized across numerous mobile standards organizations, including both 3GPP2 and WiMAX Forum NWG.

The following sections discuss specific implementations of Mobile IPv6 relative to mobile standards organizations. These sections will examine a Mobile IPv6 example from WiMAX Forum Network Working Group (NWG) standards.

WiMAX Forum NWG Implementation of Mobile IPv6

NWG R1.0 Network Architecture defines the WiMAX network architecture in support of both Client Mobile IP (CMIP) and Proxy Mobile IP (PMIP). This architecture is depicted in Figure 5-39 below, and includes the following network nodes:

Access router: The access router is the network access gateway in a WiMAX Mobile IPv6 network. This device serves as the default router for the Mobile IPv6 node.

Home agent (HA): The HA provides standards-compliant Mobile IPv6 home agent functions for mobile node session continuity.

AAA server: The AAA server provides authentication and authorization services for both the Access Service Network Gateway (ASNGW) and HA.

Mobile Internet basics: Mobile IPv6 in Practice
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Figure 5-39. WiMax network architecture

To facilitate mobility in a WiMAX network, each ASN is a unique foreign/visited network. The home agent, located in the Connectivity Service Node (CSN), provides Mobile IPv6 mobility services across all ASNs within an operator domain. The Mobile IPv6 protocol is carried across the R3 reference point in WiMAX standards.

On initial connection to the WiMAX network, the mobile node listens for Router Advertisement messages. Because there is no foreign agent function in a Mobile IPv6 network, the mobile node must acquire bootstrap information from the network infrastructure.

This is done through either DHCPv6 or through the AAA server. The Access Router can also perform access authentication and retrieve dynamic home agent assignment, home link assignment, and home address assignment information from the AAA server.

After the bootstrap information, including the home link, the Home Address (HoA), and home agent address are received, the mobile node issues a Binding Update message to the home agent. This BU message includes the following information:

Destination Option Header
MN-NAI value
MN-AAA Authentication Option

The mobile node also generates a CoA, based on the subnet it received in the Router Advertisement message. The home agent triggers an Authentication Request message to the AAA server through either RADIUS or Diameter based on information received in the BU message.

The AAA server replies with a message indicating the status (Accept/Reject) and the MNHA key for subsequent message processing. The HA also performs a replay check to ensure that the mobile node is not using expired data for authentication and responds with a Binding Acknowledgment message. This BA message includes the following information:

Type 2 Routing Header
MN-NAI Mobility Option
MN-HA Authentication Option

Figure 5-40 below illustrates a call flow for a WiMAX Mobile IPv6 session setup.

When a mobile node changes point of attachment in a WiMAX network, the access router servicing the mobile node can be changed. In this event, the mobile node must listen for, or solicit, a new Router Advertisement message. This new RA provides subnet information that the mobile node uses to determine a new CoA.

Mobile Internet basics: Mobile IPv6 in Practice
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Figure 5-40 WiMAX Mobile IPv6 Session Setup

After the CoA has been calculated, the mobile node sends a Binding Update message to the home agent. During the relocation of the R3 interface from the old access router to the new access router, a data path tunnel is established between the two access routers to ensure that no data traffic is lost. Figure 5-41 below depicts the call flow for R3 reanchoring.

Mobile Internet basics: Mobile IPv6 in Practice
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Figure 5-41. WiMax Mobile IPv6 session handoff

Figure 5-42 below illustrates the end-to-end WiMAX IPv6 protocol stack for both bidirectional tunnel and route optimization modes.

Mobile Internet basics: Mobile IPv6 in Practice
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Figure 5-42 End-to-End WiMAX Mobile IPv6 Protocol Stack

Dual-Stack Mobile IP

Mobile IPv4 and Mobile IPv6 provide technologies for mobility for mobile networks using IPv4 and IPv6 protocols, respectively. These mobility management techniques share a common name and a common function, namely, providing session continuity for a mobile node; however, the protocols themselves are indeed separate and non-interoperable.

This does not create a challenge in a network that is built on IPv4 or a network that is built on IPv6. As networks migrate from IPv4 to IPv6 for either business or technical reasons, a new challenge arises in providing session continuity as a mobile node changes point of attachment from an IPv4 domain to an IPv6 domain.

Nodes that support both IPv4 and IPv6 protocol stacks are known as dual-stack nodes. These nodes can establish connectivity through IPv4, through IPv6, or through both IPv4 and IPv6 simultaneously.

With Mobile IPv4, the node can ensure that applications reliant on IPv4 persist as the node moves from IPv4 subnet to IPv4 subnet. With Mobile IPv6, the node can ensure that applications reliant on IPv6 persist as the node moves from IPv6 subnet to IPv6 subnet. The need to support session persistence as a mobile node moves from IPv4 subnet to IPv6 subnet, or from IPv6 subnet to IPv4 subnet, requires either:

A single mobility management protocol, or
Interactions and visibility between Mobile IPv4 and Mobile IPv6 protocols.

Dual-stack mobility, a problem discussed in draft RFC draft-ietf-mip6-dsmip-problem, provides solution requirements for both Mobile IPv4 and Mobile IPv6 so that they can support mobility management for dual-stack devices.

In addition, RFC 5454, “Dual-Stack Mobile IPv4,” and RFC 5555, “Mobile IPv6 Support for Dual-Stack Hosts and Routers,” provide extensions and modifications to Mobile IPv4 and Mobile IPv6, respectively, to allow these protocols to understand and manage mobility across the IPv4 and IPv6 domains.