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RFC 4888

Network Mobility Route Optimization Problem Statement

Pages: 26
Informational
Errata

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Network Working Group                                              C. Ng
Request for Comments: 4888                      Panasonic Singapore Labs
Category: Informational                                       P. Thubert
                                                           Cisco Systems
                                                               M. Watari
                                                           KDDI R&D Labs
                                                                 F. Zhao
                                                                UC Davis
                                                               July 2007


         Network Mobility Route Optimization Problem Statement

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

With current Network Mobility (NEMO) Basic Support, all communications to and from Mobile Network Nodes must go through the bi-directional tunnel established between the Mobile Router and Home Agent when the mobile network is away. This sub-optimal routing results in various inefficiencies associated with packet delivery, such as increased delay and bottleneck links leading to traffic congestion, which can ultimately disrupt all communications to and from the Mobile Network Nodes. Additionally, with nesting of Mobile Networks, these inefficiencies get compounded, and stalemate conditions may occur in specific dispositions. This document investigates such problems and provides the motivation behind Route Optimization (RO) for NEMO.
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. NEMO Route Optimization Problem Statement . . . . . . . . . . 3 2.1. Sub-Optimality with NEMO Basic Support . . . . . . . . . . 4 2.2. Bottleneck in the Home Network . . . . . . . . . . . . . . 6 2.3. Amplified Sub-Optimality in Nested Mobile Networks . . . . 6 2.4. Sub-Optimality with Combined Mobile IPv6 Route Optimization . . . . . . . . . . . . . . . . . . . . . . . 8 2.5. Security Policy Prohibiting Traffic from Visiting Nodes . 9 2.6. Instability of Communications within a Nested Mobile Network . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.7. Stalemate with a Home Agent Nested in a Mobile Network . . 10 3. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4. Security Considerations . . . . . . . . . . . . . . . . . . . 11 5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.1. Normative Reference . . . . . . . . . . . . . . . . . . . 12 6.2. Informative Reference . . . . . . . . . . . . . . . . . . 12 Appendix A. Various Configurations Involving Nested Mobile Networks . . . . . . . . . . . . . . . . . . . . . . 13 A.1. CN Located in the Fixed Infrastructure . . . . . . . . . . 13 A.1.1. Case A: LFN and Standard IPv6 CN . . . . . . . . . . . 14 A.1.2. Case B: VMN and MIPv6 CN . . . . . . . . . . . . . . . 14 A.1.3. Case C: VMN and Standard IPv6 CN . . . . . . . . . . . 14 A.2. CN Located in Distinct Nested NEMOs . . . . . . . . . . . 15 A.2.1. Case D: LFN and Standard IPv6 CN . . . . . . . . . . . 16 A.2.2. Case E: VMN and MIPv6 CN . . . . . . . . . . . . . . . 16 A.2.3. Case F: VMN and Standard IPv6 CN . . . . . . . . . . . 16 A.3. MNN and CN Located in the Same Nested NEMO . . . . . . . . 17 A.3.1. Case G: LFN and Standard IPv6 CN . . . . . . . . . . . 18 A.3.2. Case H: VMN and MIPv6 CN . . . . . . . . . . . . . . . 18 A.3.3. Case I: VMN and Standard IPv6 CN . . . . . . . . . . . 19 A.4. CN Located Behind the Same Nested MR . . . . . . . . . . . 19 A.4.1. Case J: LFN and Standard IPv6 CN . . . . . . . . . . . 20 A.4.2. Case K: VMN and MIPv6 CN . . . . . . . . . . . . . . . 20 A.4.3. Case L: VMN and Standard IPv6 CN . . . . . . . . . . . 21 Appendix B. Example of How a Stalemate Situation Can Occur . . . 22
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1. Introduction

With current Network Mobility (NEMO) Basic Support [1], all communications to and from nodes in a mobile network must go through the bi-directional tunnel established between the Mobile Router and its Home Agent (also known as the MRHA tunnel) when the mobile network is away. Although such an arrangement allows Mobile Network Nodes to reach and be reached by any node on the Internet, limitations associated to the base protocol degrade overall performance of the network and, ultimately, can prevent all communications to and from the Mobile Network Nodes. Some of these concerns already exist with Mobile IPv6 [4] and were addressed by the mechanism known as Route Optimization, which is part of the base protocol. With Mobile IPv6, Route Optimization mostly improves the end-to-end path between the Mobile Node and Correspondent Node, with an additional benefit of reducing the load of the Home Network, thus its name. NEMO Basic Support presents a number of additional issues, making the problem more complex, so it was decided to address Route Optimization separately. In that case, the expected benefits are more dramatic, and a Route Optimization mechanism could enable connectivity that would be broken otherwise. In that sense, Route Optimization is even more important to NEMO Basic Support than it is to Mobile IPv6. This document explores limitations inherent in NEMO Basic Support, and their effects on communications between a Mobile Network Node and its corresponding peer. This is detailed in Section 2. It is expected that readers are familiar with general terminologies related to mobility in [4][2], NEMO-related terms defined in [3], and NEMO goals and requirements [5].

2. NEMO Route Optimization Problem Statement

Given the NEMO Basic Support protocol, all data packets to and from Mobile Network Nodes must go through the Home Agent, even though a shorter path may exist between the Mobile Network Node and its Correspondent Node. In addition, with the nesting of Mobile Routers, these data packets must go through multiple Home Agents and several levels of encapsulation, which may be avoided. This results in various inefficiencies and problems with packet delivery, which can ultimately disrupt all communications to and from the Mobile Network Nodes. In the following sub-sections, we will describe the effects of a pinball route with NEMO Basic Support, how it may cause a bottleneck to be formed in the Home Network, and how these get amplified with
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   nesting of mobile networks.  Closely related to nesting, we will also
   look into the sub-optimality even when Mobile IPv6 Route Optimization
   is used over NEMO Basic Support.  This is followed by a description
   of security policy in the Home Network that may forbid transit
   traffic from Visiting Mobile Nodes in mobile networks.  In addition,
   we will explore the impact of the MRHA tunnel on communications
   between two Mobile Network Nodes on different links of the same
   mobile network.  We will also provide additional motivations for
   Route Optimization by considering the potential stalemate situation
   when a Home Agent is part of a mobile network.

2.1. Sub-Optimality with NEMO Basic Support

With NEMO Basic Support, all packets sent between a Mobile Network Node and its Correspondent Node are forwarded through the MRHA tunnel, resulting in a pinball route between the two nodes. This has the following sub-optimal effects: o Longer Route Leading to Increased Delay and Additional Infrastructure Load Because a packet must transit from a mobile network to the Home Agent then to the Correspondent Node, the transit time of the packet is usually longer than if the packet were to go straight from the mobile network to the Correspondent Node. When the Correspondent Node (or the mobile network) resides near the Home Agent, the increase in packet delay can be very small. However, when the mobile network and the Correspondent Node are relatively near to one another but far away from the Home Agent on the Internet, the increase in delay is very large. Applications such as real-time multimedia streaming may not be able to tolerate such increase in packet delay. In general, the increase in delay may also impact the performance of transport protocols such as TCP, since the sending rate of TCP is partly determined by the round- trip time (RTT) perceived by the communication peers. Moreover, by using a longer route, the total resource utilization for the traffic would be much higher than if the packets were to follow a direct path between the Mobile Network Node and Correspondent Node. This would result in additional load in the infrastructure. o Increased Packet Overhead The encapsulation of packets in the MRHA tunnel results in increased packet size due to the addition of an outer header. This reduces the bandwidth efficiency, as an IPv6 header can be
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      quite substantial relative to the payload for applications such as
      voice samples.  For instance, given a voice application using an 8
      kbps algorithm (e.g., G.729) and taking a voice sample every 20 ms
      (as in RFC 1889 [6]), the packet transmission rate will be 50
      packets per second.  Each additional IPv6 header is an extra 320
      bits per packet (i.e., 16 kbps), which is twice the actual
      payload!

   o  Increased Processing Delay

      The encapsulation of packets in the MRHA tunnel also results in
      increased processing delay at the points of encapsulation and
      decapsulation.  Such increased processing may include encryption/
      decryption, topological correctness verifications, MTU
      computation, fragmentation, and reassembly.

   o  Increased Chances of Packet Fragmentation

      The augmentation in packet size due to packet encapsulation may
      increase the chances of the packet being fragmented along the MRHA
      tunnel.  This can occur if there is no prior path MTU discovery
      conducted, or if the MTU discovery mechanism did not take into
      account the encapsulation of packets.  Packet fragmentation will
      result in a further increase in packet delays and further
      reduction of bandwidth efficiency.

   o  Increased Susceptibility to Link Failure

      Under the assumption that each link has the same probability of
      link failure, a longer routing path would be more susceptible to
      link failure.  Thus, packets routed through the MRHA tunnel may be
      subjected to a higher probability of being lost or delayed due to
      link failure, compared to packets that traverse directly between
      the Mobile Network Node and its Correspondent Node.
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2.2. Bottleneck in the Home Network

Apart from the increase in packet delay and infrastructure load, forwarding packets through the Home Agent may also lead to either the Home Agent or the Home Link becoming a bottleneck for the aggregated traffic from/to all the Mobile Network Nodes. A congestion at home would lead to additional packet delay, or even packet loss. In addition, Home Agent operations such as security check, packet interception, and tunneling might not be as optimized in the Home Agent software as plain packet forwarding. This could further limit the Home Agent capacity for data traffic. Furthermore, with all traffic having to pass through the Home Link, the Home Link becomes a single point of failure for the mobile network. Data packets that are delayed or discarded due to congestion at the Home Network would cause additional performance degradation to applications. Signaling packets, such as Binding Update messages, that are delayed or discarded due to congestion at the Home Network may affect the establishment or update of bi-directional tunnels, causing disruption of all traffic flow through these tunnels. A NEMO Route Optimization mechanism that allows the Mobile Network Nodes to communicate with their Correspondent Nodes via a path that is different from the MRHA tunneling and thereby avoiding the Home Agent may alleviate or even prevent the congestion at the Home Agent or Home Link.

2.3. Amplified Sub-Optimality in Nested Mobile Networks

By allowing other mobile nodes to join a mobile network, and in particular mobile routers, it is possible to form arbitrary levels of nesting of mobile networks. With such nesting, the use of NEMO Basic Support further amplifies the sub-optimality of routing. We call this the amplification effect of nesting, where the undesirable effects of a pinball route with NEMO Basic Support are amplified with each level of nesting of mobile networks. This is best illustrated by an example shown in Figure 1.
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               +--------+  +--------+  +--------+  +--------+
               | MR2_HA |  | MR3_HA |  | MR4_HA |  | MR5_HA |
               +------+-+  +---+----+  +---+----+  +-+------+
                       \       |           |        /
        +--------+    +------------------------------+
        | MR1_HA |----|         Internet             |-----CN1
        +--------+    +------------------------------+
                                    |
                                +---+---+
                      root-MR   |  MR1  |
                                +-------+
                                 |     |
                          +-------+   +-------+
                 sub-MR   |  MR2  |   |  MR4  |
                          +---+---+   +---+---+
                              |           |
                          +---+---+   +---+---+
                 sub-MR   |  MR3  |   |  MR5  |
                          +---+---+   +---+---+
                              |           |
                          ----+----   ----+----
                             MNN         CN2

              Figure 1: An Example of a Nested Mobile Network

   Using NEMO Basic Support, the flow of packets between a Mobile
   Network Node, MNN, and a Correspondent Node, CN1, would need to go
   through three separate tunnels, illustrated in Figure 2 below.

                                ----------.
                      ---------/         /----------.
              -------/        |         |          /-------
    MNN -----( -  - | -  -  - | -  -  - | -  -  - |  -  - (------ CN1
           MR3-------\        |         |          \-------MR3_HA
                    MR2--------\         \----------MR2_HA
                              MR1---------MR1_HA

                Figure 2: Nesting of Bi-Directional Tunnels
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   This leads to the following problems:

   o  Pinball Route

      Both inbound and outbound packets will flow via the Home Agents of
      all the Mobile Routers on their paths within the mobile network,
      with increased latency, less resilience, and more bandwidth usage.
      Appendix A illustrates in detail the packets' routes under
      different nesting configurations of the Mobile Network Nodes.

   o  Increased Packet Size

      An extra IPv6 header is added per level of nesting to all the
      packets.  The header compression suggested in [7] cannot be
      applied because both the source and destination (the intermediate
      Mobile Router and its Home Agent) are different hop to hop.

   Nesting also amplifies the probability of congestion at the Home
   Networks of the upstream Mobile Routers.  In addition, the Home Link
   of each upstream Mobile Router will also be a single point of failure
   for the nested Mobile Router.

2.4. Sub-Optimality with Combined Mobile IPv6 Route Optimization

When a Mobile IPv6 host joins a mobile network, it becomes a Visiting Mobile Node of the mobile network. Packets sent to and from the Visiting Mobile Node will have to be routed not only via the Home Agent of the Visiting Mobile Node, but also via the Home Agent of the Mobile Router in the mobile network. This suffers the same amplification effect of nested mobile network mentioned in Section 2.3. In addition, although Mobile IPv6 [4] allows a mobile host to perform Route Optimization with its Correspondent Node in order to avoid tunneling with its Home Agent, the "optimized" route is no longer optimized when the mobile host is attached to a mobile network. This is because the route between the mobile host and its Correspondent Node is subjected to the sub-optimality introduced by the MRHA tunnel. Interested readers may refer to Appendix A for examples of how the routes will appear with nesting of Mobile IPv6 hosts in mobile networks. The readers should also note that the same sub-optimality would apply when the mobile host is outside the mobile network and its Correspondent Node is in the mobile network.
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2.5. Security Policy Prohibiting Traffic from Visiting Nodes

NEMO Basic Support requires all traffic from visitors to be tunneled to the Mobile Router's Home Agent. This might represent a breach in the security of the Home Network (some specific attacks against the Mobile Router's binding by rogue visitors have been documented in [8][9]). Administrators might thus fear that malicious packets will be routed into the Home Network via the bi-directional tunnel. As a consequence, it can be expected that in many deployment scenarios, policies will be put in place to prevent unauthorized Visiting Mobile Nodes from attaching to the Mobile Router. However, there are deployment scenarios where allowing unauthorized Visiting Mobile Nodes is actually desirable. For instance, when Mobile Routers attach to other Mobile Routers and form a nested NEMO, they depend on each other to reach the Internet. When Mobile Routers have no prior knowledge of one another (no security association, Authentication, Authorization, and Accounting (AAA), Public-Key Infrastructure (PKI), etc.), it could still be acceptable to forward packets, provided that the packets are not tunneled back to the Home Networks. A Route Optimization mechanism that allows traffic from Mobile Network Nodes to bypass the bi-directional tunnel between a Mobile Router and its Home Agent would be a necessary first step towards a Tit for Tat model, where MRs would benefit from a reciprocal altruism, based on anonymity and innocuousness, to extend the Internet infrastructure dynamically.

2.6. Instability of Communications within a Nested Mobile Network

Within a nested mobile network, two Mobile Network Nodes may communicate with each other. Let us consider the previous example illustrated in Figure 1 where MNN and CN2 are sharing a communication session. With NEMO Basic Support, a packet sent from MNN to CN2 will need to be forwarded to the Home Agent of each Mobile Router before reaching CN2, whereas, a packet following the direct path between them need not even leave the mobile network. Readers are referred to Appendix A.3 for detailed illustration of the resulting routing paths. Apart from the consequences of increased packet delay and packet size, which are discussed in previous sub-sections, there are two additional effects that are undesirable: o when the nested mobile network is disconnected from the Internet (e.g., MR1 loses its egress connectivity), MNN and CN2 can no
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      longer communicate with each other, even though the direct path
      from MNN to CN2 is unaffected;

   o  the egress link(s) of the root Mobile Router (i.e., MR1) becomes a
      bottleneck for all the traffic that is coming in and out of the
      nested mobile network.

   A Route Optimization mechanism could allow traffic between two Mobile
   Network Nodes nested within the same mobile network to follow a
   direct path between them, without being routed out of the mobile
   network.  This may also off-load the processing burden of the
   upstream Mobile Routers when the direct path between the two Mobile
   Network Nodes does not traverse these Mobile Routers.

2.7. Stalemate with a Home Agent Nested in a Mobile Network

Several configurations for the Home Network are described in [10]. In particular, there is a mobile home scenario where a (parent) Mobile Router is also a Home Agent for its mobile network. In other words, the mobile network is itself an aggregation of Mobile Network Prefixes assigned to (children) Mobile Routers. A stalemate situation exists in the case where the parent Mobile Router visits one of its children. The child Mobile Router cannot find its Home Agent in the Internet and thus cannot establish its MRHA tunnel and forward the visitor's traffic. The traffic from the parent is thus blocked from reaching the Internet, and it will never bind to its own (grandparent) Home Agent. Appendix B gives a detailed illustration of how such a situation can occur. Then again, a Route Optimization mechanism that bypasses the nested tunnel might enable the parent traffic to reach the Internet and let it bind. At that point, the child Mobile Router would be able to reach its parent and bind in turn. Additional nested Route Optimization solutions might also enable the child to locate its Home Agent in the nested structure and bind regardless of whether or not the Internet is reachable.

3. Conclusion

With current NEMO Basic Support, all communications to and from Mobile Network Nodes must go through the MRHA tunnel when the mobile network is away. This results in various inefficiencies associated with packet delivery. This document investigates such inefficiencies and provides the motivation behind Route Optimization for NEMO.
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   We have described the sub-optimal effects of pinball routes with NEMO
   Basic Support, how they may cause a bottleneck to be formed in the
   Home Network, and how they get amplified with nesting of mobile
   networks.  These effects will also be seen even when Mobile IPv6
   Route Optimization is used over NEMO Basic Support.  In addition,
   other issues concerning the nesting of mobile networks that might
   provide additional motivation for a NEMO Route Optimization mechanism
   were also explored, such as the prohibition of forwarding traffic
   from a Visiting Mobile Node through an MRHA tunnel due to security
   concerns, the impact of the MRHA tunnel on communications between two
   Mobile Network Nodes on different links of the same mobile network,
   and the possibility of a stalemate situation when Home Agents are
   nested within a mobile network.

4. Security Considerations

This document highlights some limitations of NEMO Basic Support. In particular, some security concerns could prevent interesting applications of the protocol, as detailed in Section 2.5. Route Optimization for RFC 3963 [1] might introduce new threats, just as it might alleviate existing ones. This aspect will certainly be a key criterion in the evaluation of the proposed solutions.

5. Acknowledgments

The authors wish to thank the co-authors of previous versions from which this document is derived: Marco Molteni, Paik Eun-Kyoung, Hiroyuki Ohnishi, Thierry Ernst, Felix Wu, and Souhwan Jung. Early work by Masafumi Watari on the extracted appendix was written while still at Keio University. In addition, sincere appreciation is also extended to Jari Arkko, Carlos Bernardos, Greg Daley, T.J. Kniveton, Henrik Levkowetz, Erik Nordmark, Alexandru Petrescu, Hesham Soliman, Ryuji Wakikawa, and Patrick Wetterwald for their various contributions.
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6. References

6.1. Normative Reference

[1] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert, "Network Mobility (NEMO) Basic Support Protocol", RFC 3963, January 2005. [2] Manner, J. and M. Kojo, "Mobility Related Terminology", RFC 3753, June 2004. [3] Ernst, T. and H. Lach, "Network Mobility Support Terminology", RFC 4885, July 2007.

6.2. Informative Reference

[4] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. [5] Ernst, T., "Network Mobility Support Goals and Requirements", RFC 4886, July 2007. [6] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", RFC 1889, January 1996. [7] Deering, S. and B. Zill, "Redundant Address Deletion when Encapsulating IPv6 in IPv6", Work in Progress, November 2001. [8] Petrescu, A., Olivereau, A., Janneteau, C., and H-Y. Lach, "Threats for Basic Network Mobility Support (NEMO threats)", Work in Progress, January 2004. [9] Jung, S., Zhao, F., Wu, S., Kim, H-G., and S-W. Sohn, "Threat Analysis on NEMO Basic Operations", Work in Progress, July 2004. [10] Thubert, P., Wakikawa, R., and V. Devarapalli, "Network Mobility Home Network Models", RFC RFC4887, July 2007. [11] Draves, R., "Default Address Selection for Internet Protocol version 6 (IPv6)", RFC 3484, February 2003.
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Appendix A. Various Configurations Involving Nested Mobile Networks

In the following sections, we try to describe different communication models that involve a nested mobile network and to clarify the issues for each case. We illustrate the path followed by packets if we assume nodes only use Mobile IPv6 and NEMO Basic Support mechanisms. Different cases are considered where a Correspondent Node is located in the fixed infrastructure, in a distinct nested mobile network as the Mobile Network Node, or in the same nested mobile network as the Mobile Network Node. Additionally, cases where Correspondent Nodes and Mobile Network Nodes are either standard IPv6 nodes or Mobile IPv6 nodes are considered. As defined in [3], standard IPv6 nodes are nodes with no mobility functions whatsoever, i.e., they are not Mobile IPv6 or NEMO enabled. This means that they cannot move around keeping open connections and that they cannot process Binding Updates sent by peers.

A.1. CN Located in the Fixed Infrastructure

The most typical configuration is the case where a Mobile Network Node communicates with a Correspondent Node attached in the fixed infrastructure. Figure 3 below shows an example of such topology. +--------+ +--------+ +--------+ | MR1_HA | | MR2_HA | | MR3_HA | +---+----+ +---+----+ +---+----+ | | | +-------------------------+ | Internet |----+ CN +-------------------------+ | | +---+---+ +--+-----+ root-MR | MR1 | | VMN_HA | +---+---+ +--------+ | +---+---+ sub-MR | MR2 | +---+---+ | +---+---+ sub-MR | MR3 | +---+---+ | ----+---- MNN Figure 3: CN Located at the Infrastructure
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A.1.1. Case A: LFN and Standard IPv6 CN

The simplest case is where both MNN and CN are fixed nodes with no mobility functions. That is, MNN is a Local Fixed Node, and CN is a standard IPv6 node. Packets are encapsulated between each Mobile Router and its respective Home Agent (HA). As shown in Figure 4, in such a case, the path between the two nodes would go through: 1 2 3 4 3 2 1 MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA --- CN LFN IPv6 Node The digits represent the number of IPv6 headers. Figure 4: MNN and CN Are Standard IPv6 Nodes

A.1.2. Case B: VMN and MIPv6 CN

In this second case, both end nodes are Mobile IPv6-enabled mobile nodes, that is, MNN is a Visiting Mobile Node. Mobile IPv6 Route Optimization may thus be initiated between the two and packets would not go through the Home Agent of the Visiting Mobile Node or the Home Agent of the Correspondent Node (not shown in the figure). However, packets will still be tunneled between each Mobile Router and its respective Home Agent, in both directions. As shown in Figure 5, the path between MNN and CN would go through: 1 2 3 4 3 2 1 MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA --- CN VMN MIPv6 Figure 5: MNN and CN Are MIPv6 Mobile Nodes

A.1.3. Case C: VMN and Standard IPv6 CN

When the communication involves a Mobile IPv6 node either as a Visiting Mobile Node or as a Correspondent Node, Mobile IPv6 Route Optimization cannot be performed because the standard IPv6 Correspondent Node cannot process Mobile IPv6 signaling. Therefore, MNN would establish a bi-directional tunnel with its HA, which causes the flow to go out the nested NEMO. Packets between MNN and CN would thus go through MNN's own Home Agent (VMN_HA). The path would therefore be as shown in Figure 6:
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               2       3       4       5          4
          MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA
          VMN                                           |
                                                        | 3
                                       1          2     |
                                   CN --- VMN_HA --- MR3_HA
                                IPv6 Node


   Figure 6: MNN is an MIPv6 Mobile Node and CN is a Standard IPv6 Node

   Providing Route Optimization involving a Mobile IPv6 node may require
   optimization among the Mobile Routers and the Mobile IPv6 node.

A.2. CN Located in Distinct Nested NEMOs

The Correspondent Node may be located in another nested mobile network, different from the one MNN is attached to, as shown in Figure 7. We define such configuration as "distinct nested mobile networks". +--------+ +--------+ +--------+ +--------+ | MR2_HA | | MR3_HA | | MR4_HA | | MR5_HA | +------+-+ +---+----+ +---+----+ +-+------+ \ | | / +--------+ +-------------------------+ +--------+ | MR1_HA |----| Internet |----| VMN_HA | +--------+ +-------------------------+ +--------+ | | +---+---+ +---+---+ root-MR | MR1 | | MR4 | +---+---+ +---+---+ | | +---+---+ +---+---+ sub-MR | MR2 | | MR5 | +---+---+ +---+---+ | | +---+---+ ----+---- sub-MR | MR3 | CN +---+---+ | ----+---- MNN Figure 7: MNN and CN Located in Distinct Nested NEMOs
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A.2.1. Case D: LFN and Standard IPv6 CN

Similar to Case A, we start off with the case where both end nodes do not have any mobility functions. Packets are encapsulated at every Mobile Router on the way out of the nested mobile network, decapsulated by the Home Agents, and then encapsulated again on their way down the nested mobile network. 1 2 3 4 3 2 MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA LFN | | 1 1 2 3 2 | CN --- MR5 --- MR4 --- MR4_HA --- MR5_HA IPv6 Node Figure 8: MNN and CN Are Standard IPv6 Nodes

A.2.2. Case E: VMN and MIPv6 CN

Similar to Case B, when both end nodes are Mobile IPv6 nodes, the two nodes may initiate Mobile IPv6 Route Optimization. Again, packets will not go through the Home Agent of the MNN or the Home Agent of the Mobile IPv6 Correspondent Node (not shown in the figure). However, packets will still be tunneled for each Mobile Router to its Home Agent and vice versa. Therefore, the path between MNN and CN would go through: 1 2 3 4 3 2 MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA VMN | | 1 1 2 3 2 | CN --- MR5 --- MR4 --- MR4_HA --- MR5_HA MIPv6 Node Figure 9: MNN and CN Are MIPv6 Mobile Nodes

A.2.3. Case F: VMN and Standard IPv6 CN

Similar to Case C, when the communication involves a Mobile IPv6 node either as a Visiting Mobile Node or as a Correspondent Node, MIPv6 Route Optimization cannot be performed because the standard IPv6 Correspondent Node cannot process Mobile IPv6 signaling. MNN would
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   therefore establish a bi-directional tunnel with its Home Agent.
   Packets between MNN and CN would thus go through MNN's own Home Agent
   as shown in Figure 10:



            2       3       4       5          4          3
       MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA
       VMN                                                      |
                                                                | 2
                   1       2       3           2          1     |
               CN --- MR5 --- MR4 --- MR4_HA  --- MR5_HA --- VMN_HA
            IPv6 Node


   Figure 10: MNN is an MIPv6 Mobile Node and CN is a Standard IPv6 Node

A.3. MNN and CN Located in the Same Nested NEMO

Figure 11 below shows the case where the two communicating nodes are connected behind different Mobile Routers that are connected in the same nested mobile network, and thus behind the same root Mobile Router. Route Optimization can avoid packets being tunneled outside the nested mobile network. +--------+ +--------+ +--------+ +--------+ | MR2_HA | | MR3_HA | | MR4_HA | | MR5_HA | +------+-+ +---+----+ +---+----+ +-+------+ \ | | / +--------+ +-------------------------+ +--------+ | MR1_HA |----| Internet |----| VMN_HA | +--------+ +-------------------------+ +--------+ | +---+---+ root-MR | MR1 | +-------+ | | +-------+ +-------+ sub-MR | MR2 | | MR4 | +---+---+ +---+---+ | | +---+---+ +---+---+ sub-MR | MR3 | | MR5 | +---+---+ +---+---+ | | ----+---- ----+---- MNN CN
Top   ToC   RFC4888 - Page 18
           Figure 11: MNN and CN Located in the Same Nested NEMO

A.3.1. Case G: LFN and Standard IPv6 CN

Again, we start off with the case where both end nodes do not have any mobility functions. Packets are encapsulated at every Mobile Router on the way out of the nested mobile network via the root Mobile Router, decapsulated and encapsulated by the Home Agents, and then make their way back to the nested mobile network through the same root Mobile Router. Therefore, the path between MNN and CN would go through: 1 2 3 4 3 2 MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA LFN | | 1 1 2 3 4 3 2 | CN --- MR5 --- MR4 --- MR1 --- MR1_HA --- MR4_HA --- MR5_HA IPv6 Node Figure 12: MNN and CN Are Standard IPv6 nodes

A.3.2. Case H: VMN and MIPv6 CN

Similar to Case B and Case E, when both end nodes are Mobile IPv6 nodes, the two nodes may initiate Mobile IPv6 Route Optimization, which will avoid the packets going through the Home Agent of MNN or the Home Agent of the Mobile IPv6 CN (not shown in the figure). However, packets will still be tunneled between each Mobile Router and its respective Home Agent in both directions. Therefore, the path would be the same as with Case G and go through: 1 2 3 4 3 2 MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA LFN | | 1 1 2 3 4 3 2 | CN --- MR5 --- MR4 --- MR1 --- MR1_HA --- MR4_HA --- MR5_HA MIPv6 Node Figure 13: MNN and CN Are MIPv6 Mobile Nodes
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A.3.3. Case I: VMN and Standard IPv6 CN

As for Case C and Case F, when the communication involves a Mobile IPv6 node either as a Visiting Mobile Node or as a Correspondent Node, Mobile IPv6 Route Optimization cannot be performed. Therefore, MNN will establish a bi-directional tunnel with its Home Agent. Packets between MNN and CN would thus go through MNN's own Home Agent. The path would therefore be as shown in Figure 14: 2 3 4 5 4 3 MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA VMN | | 2 | VMN_HA | | 1 1 2 3 4 3 2 | CN --- MR5 --- MR4 --- MR1 --- MR1_HA --- MR4_HA --- MR5_HA IPv6 Node Figure 14: MNN is an MIPv6 Mobile Node and CN is a Standard IPv6 Node

A.4. CN Located Behind the Same Nested MR

Figure 15 below shows the case where the two communicating nodes are connected behind the same nested Mobile Router. The optimization is required when the communication involves MIPv6-enabled nodes.
Top   ToC   RFC4888 - Page 20
              +--------+  +--------+  +--------+  +--------+
              | MR2_HA |  | MR3_HA |  | MR4_HA |  | MR5_HA |
              +------+-+  +---+----+  +---+----+  +-+------+
                      \       |           |        /
         +--------+    +-------------------------+    +--------+
         | MR1_HA |----|        Internet         |----| VMN_HA |
         +--------+    +-------------------------+    +--------+
                                    |
                                +---+---+
                      root-MR   |  MR1  |
                                +---+---+
                                    |
                                +-------+
                       sub-MR   |  MR2  |
                                +---+---+
                                    |
                                +---+---+
                       sub-MR   |  MR3  |
                                +---+---+
                                    |
                                -+--+--+-
                                MNN    CN

          Figure 15: MNN and CN Located Behind the Same Nested MR

A.4.1. Case J: LFN and Standard IPv6 CN

If both end nodes are Local Fixed Nodes, no special function is necessary for optimization of their communications. The path between the two nodes would go through: 1 MNN --- CN LFN IPv6 Node Figure 16: MNN and CN Are Standard IPv6 Nodes

A.4.2. Case K: VMN and MIPv6 CN

Similar to Case H, when both end nodes are Mobile IPv6 nodes, the two nodes may initiate Mobile IPv6 Route Optimization. Although few packets would go out the nested mobile network for the Return Routability initialization, however, unlike Case B and Case E, packets will not get tunneled outside the nested mobile network. Therefore, packets between MNN and CN would eventually go through:
Top   ToC   RFC4888 - Page 21
                                  1
                             MNN --- CN
                             VMN   MIPv6 Node


               Figure 17: MNN and CN are MIPv6 Mobile Nodes

   If the root Mobile Router is disconnected while the nodes exchange
   keys for the Return Routability procedure, they may not communicate
   even though they are connected on the same link.

A.4.3. Case L: VMN and Standard IPv6 CN

When the communication involves a Mobile IPv6 node either as a Visiting Mobile Network Node or as a Correspondent Node, Mobile IPv6 Route Optimization cannot be performed. Therefore, even though the two nodes are on the same link, MNN will establish a bi-directional tunnel with its Home Agent, which causes the flow to go out the nested mobile network. The path between MNN and CN would require another Home Agent (VMN_HA) to go through for this Mobile IPv6 node: 2 3 4 5 4 3 MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA VMN | | 2 | VMN_HA | | 1 1 2 3 4 3 2 | CN --- MR5 --- MR4 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA IPv6 Node Figure 18: MNN is an MIPv6 Mobile Node and CN is a Standard IPv6 Node However, MNN may also decide to use its Care-of Address (CoA) as the source address of the packets, thus avoiding the tunneling with the MNN's Home Agent. This is particularly useful for a short-term communications that may easily be retried if it fails. Default Address Selection [11] provides some mechanisms for controlling the choice of the source address.
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Appendix B. Example of How a Stalemate Situation Can Occur

Section 2.7 describes the occurrence of a stalemate situation where a Home Agent of a Mobile Router is nested behind the Mobile Router. Here, we illustrate a simple example where such a situation can occur. Consider a mobility configuration depicted in Figure 19 below. MR1 is served by HA1/BR and MR2 is served by HA2. The 'BR' designation indicates that HA1 is a border router. Both MR1 and MR2 are at home in the initial step. HA2 is placed inside the first mobile network, thus representing a "mobile" Home Agent. /-----CN +----------+ home link 1 +--------+ | | ----+-----------------| HA1/BR |---| Internet | | +--------+ | | | +----------+ +--+--+ +-----+ | MR1 | | HA2 | +--+--+ +--+--+ | | -+--------+-- mobile net 1 / home link 2 | +--+--+ +--+--+ | MR2 | | LFN | +--+--+ +--+--+ | | -+--------+- mobile net 2 Figure 19: Initial Deployment In Figure 19 above, communications between CN and LFN follow a direct path as long as both MR1 and MR2 are positioned at home. No encapsulation intervenes. In the next step, consider that the MR2's mobile network leaves home and visits a foreign network, under Access Router (AR) like in Figure 20 below.
Top   ToC   RFC4888 - Page 23
                                               /-----CN
                                   +----------+
        home link 1   +--------+   |          |
        --+-----------| HA1/BR |---| Internet |
          |           +--------+   |          |
       +--+--+  +-----+            +----------+
       | MR1 |  | HA2 |                        \
       +--+--+  +--+--+                        +-----+
          |        |                           | AR  |
         -+--------+- mobile net 1             +--+--+
                      home link 2                 |
                                               +--+--+  +-----+
                                               | MR2 |  | LFN |
                                               +--+--+  +--+--+
                                                  |        |
                                    mobile net 2 -+--------+-

                  Figure 20: Mobile Network 2 Leaves Home

   Once MR2 acquires a Care-of Address under AR, the tunnel setup
   procedure occurs between MR2 and HA2.  MR2 sends a Binding Update to
   HA2 and HA2 replies with a Binding Acknowledgement to MR2.  The bi-
   directional tunnel has MR2 and HA2 as tunnel endpoints.  After the
   tunnel MR2HA2 has been set up, the path taken by a packet from CN
   towards LFN can be summarized as:

       CN->BR->MR1->HA2=>MR1=>BR=>AR=>MR2->LFN.

   Non-encapsulated packets are marked "->" while encapsulated packets
   are marked "=>".

   Consider next the attachment of the first mobile network under the
   second mobile network, like in Figure 21 below.

   After this movement, MR1 acquires a Care-of Address valid in the
   second mobile network.  Subsequently, it sends a Binding Update (BU)
   message addressed to HA1.  This Binding Update is encapsulated by MR2
   and sent towards HA2, which is expected to be placed in mobile net 1
   and expected to be at home.  Once HA1/BR receives this encapsulated
   BU, it tries to deliver to MR1.  Since MR1 is not at home, and a
   tunnel has not yet been set up between MR1 and HA1, HA1 is not able
   to route this packet and drops it.  Thus, the tunnel establishment
   procedure between MR1 and HA1 is not possible, because the tunnel
   between MR2 and HA2 had been previously torn down (when the mobile
   net 1 moved from home).  The communications between CN and LFN stops,
   even though both mobile networks are connected to the Internet.
Top   ToC   RFC4888 - Page 24
                                      /-----CN
                          +----------+
             +--------+   |          |
             | HA1/BR |---| Internet |
             +--------+   |          |
                          +----------+
                                      \
                                      +-----+
                                      | AR  |
                                      +--+--+
                                         |
                                      +--+--+  +-----+
                                      | MR2 |  | LFN |
                                      +--+--+  +--+--+
                                         |        |
                           mobile net 2 -+--------+-
                                         |
                                      +--+--+  +-----+
                                      | MR1 |  | HA2 |
                                      +--+--+  +--+--+
                                         |        |
                           mobile net 1 -+--------+-

                   Figure 21: Stalemate Situation Occurs

   If both tunnels between MR1 and HA1, and between MR2 and HA2, were up
   simultaneously, they would have "crossed over" each other.  If the
   tunnels MR1-HA1 and MR2-HA2 were drawn in Figure 21, it could be
   noticed that the path of the tunnel MR1-HA1 includes only one
   endpoint of the tunnel MR2-HA2 (the MR2 endpoint).  Two MR-HA tunnels
   are crossing over each other if the IP path between two endpoints of
   one tunnel includes one and only one endpoint of the other tunnel
   (assuming that both tunnels are up).  When both endpoints of one
   tunnel are included in the path of the other tunnel, then tunnels are
   simply encapsulating each other.
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Authors' Addresses

Chan-Wah Ng Panasonic Singapore Laboratories Pte Ltd Blk 1022 Tai Seng Ave #06-3530 Tai Seng Industrial Estate, Singapore 534415 SG Phone: +65 65505420 EMail: chanwah.ng@sg.panasonic.com Pascal Thubert Cisco Systems Village d'Entreprises Green Side 400, Avenue de Roumanille Batiment T3, Biot - Sophia Antipolis 06410 FRANCE EMail: pthubert@cisco.com Masafumi Watari KDDI R&D Laboratories Inc. 2-1-15 Ohara Fujimino, Saitama 356-8502 JAPAN EMail: watari@kddilabs.jp Fan Zhao UC Davis One Shields Avenue Davis, CA 95616 US Phone: +1 530 752 3128 EMail: fanzhao@ucdavis.edu
Top   ToC   RFC4888 - Page 26
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