Mobile Internet basics: Mobile IPv6 in Practice - Embedded.com

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.


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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.


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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.


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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.


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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.

Mobile IPv4 Extensions to Support IPv6
The extensions to Mobile IPv4 in support of IPv6 allow the mobile node to maintain connectivity using only the Mobile IPv4 protocol while moving in an IPv4 or dual-stack network. These extensions provide separation between the signaling protocol (Mobile IPv4) and the IP transport network that tunnels it. This allows Mobile IPv4 to establish both IPv4 and IPv6 tunnels over the IPv4 transport network.

(Note: Because the signaling protocol is Mobile IPv4, the required mode of operation to support both IPv4 and IPv6 is reverse tunneling or bidirectional tunneling. The route optimization mode provided by Mobile IPv6 cannot be used, because correspondent nodes in a Mobile IPv4 network are unaware of the mobility signaling .)

The mobile node communicates information about the IPv6 prefixes to the Mobile IPv4 home agent through RRQ/RRP extensions. Three extensions are added to the RRQ/RRP flows:

IPv6 Prefix Request : The mobile node can include one or more of the IPv6 Prefix Request extensions in an RRQ message. This extensions carries information about the IPv6 prefixes that the mobile node is using.

IPv6 Prefix Reply: The Mobile IPv4 home agent responds to the IPv6 Prefix Request in the RRQ with an IPv6 Prefix Reply in the RRP. This extension notifies the mobile node whether the request was accepted or rejected.

IPv6 Tunneling Mode: The mobile node includes a single IPv6 Tunneling Mode extension in an RRQ message. This extension notifies the home agent as to which tunneling protocol should be used for tunneling IPv6 packets.

Upon successful registration to a Mobile IPv4 home agent, a dual-stack mobile node can receive traffic for either its IPv4 home address or IPv6 home address through the mobile IPv4 tunnel to the home agent.

Because the home agent encapsulates this traffic in Mobile IPv4, the traffic can even traverse a foreign agent (if foreign agent CoA is negotiated). Figure 5-43 below illustrates Mobile IPv4 being used to tunnel IPv6 traffic to a mobile node.


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Figure 5-43 Mobile IPv4 Tunneling IPv6 Packets

Mobile IPv6 Extensions to Support IPv4
The options added to Mobile IPv6 in support of IPv4 allow the mobile node to maintain connectivity using only the Mobile IPv6 protocol while moving in an IPv4 or dual-stack network. Like the extensions for Mobile IPv4 RRQ/RRP, these options to the Mobile IPv6 Binding Update and Acknowledgment headers allow the mobile node to use a single mobility management protocol (Mobile IPv6) while changing point of attachment.

A dual-stack mobile node updates the home agent with its IPv6 CoA. The home agent creates a binding cache entry for each home address, IPv4 and IPv6, to this CoA. These Binding Updates can be sent to the home agent through IPv6, or encapsulated in IPv4, depending on the network protocol support within the foreign network.

(Note: Because the signaling protocol is Mobile IPv6, the mobile node can use router optimization mode when communicating through an IPv6 CoA with a node that supports Mobile IPv6. If the mobile node is located in a foreign network that does not support IPv6, or is communicating with an IPv4 correspondent node, bidirectional tunneling mode is used .)

The options added to the Binding Update header include the following:

IPv4 Home Address Option: This option notifies the Mobile IPv6 home agent of the mobile node’s IPv4 home address. The Mobile IPv6 home agent can also provide dynamic IPv4 home address assignment for the mobile node.

I Pv4 CoA Option: This option notifies the Mobile IPv6 home agent of the mobile node’s current IPv4 CoA when the mobile node is located in a network that only supports IPv4.


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Figure 5-44 Mobile IPv6 Tunneling IPv4 Packets

The Binding Acknowledgment Header also includes the IPv4 Address Acknowledgment Option. This option notifies the mobile node that the home agent has created a binding entry for the mobile node’s IPv4 home address. If the home agent assigned this address dynamically, it includes this IP address to notify the mobile node. If the mobile node had specified a home address, the home agent copies the value from the IPv4 Home Address Option in the Binding Update message.

Figure 5-44 above illustrates Mobile IPv4 being used to tunnel IPv6 traffic to a mobile node.

Next in Part 6 : IkeV3 AND MOBIKE Technology Overview
To read Part 1 , go to “ Transport layer mobility challenges .”
To read Part 2, go to “Mobile IPv4 registration and AAA.
To read Part 3, go to “Mobile IPv4 tunners,bindings and diagrams.
To read Part 4, go to Mobile IPv6 Technology Overview

This series of articles is from the book “Building the Mobile Internet”, by Mark Grayson, KevinShatzkamer and Klass Wierenga.Copyright 2011, used by permission of PearsonEducation, Inc.. Written permission from Pearson Education, Inc. is required forall other uses.

Mark Grayson is a distinguished consulting engineer atCisco Systems with responsibility for leading Cisco’smobile architecture strategy. With 20 years experience in the wireless industry,he holds first class honors in electronics and communications engineering fromthe University of Birmingham (England) as well as a PhD, in radio engineering.

Kevin Shatzkamer is a distinguished system architect atCisco Systems with responsibility for long term strategy and architecturalevolution of mobile wireless networks. He holds a Bachelor of engineering degreefrom the University of Floriga and a MBA from Indiana University.

Klaas Wierenga is a senior consulting engineer in theoffice of the CTO at Cisco. His 15 plus years of experience include planning,analysis and design of systems in the fields of mobility, security and identify.He holds a Master’s degree in consumer science from the University of Groningen,The Netherlands.

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