NEMO Working Group C. Ng Internet-Draft Panasonic Singapore Labs Expires: January 19, 2006 E. Paik KT T. Ernst WIDE at Keio University M. Bagnulo UC3M July 18, 2005 Analysis of Multihoming in Network Mobility Support draft-ietf-nemo-multihoming-issues-03 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 19, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This document is an analysis of multihoming in the context of network mobility (NEMO) in IPv6. As there are many situations in which mobile networks may be multihomed, a taxonomy is proposed to classify Ng, et al. Expires January 19, 2006 [Page 1] Internet-Draft Analysis of Multihoming in NEMO July 2005 the possible configurations. The possible deployment scenarios of multihomed mobile networks are described together with the associated issues when network mobility is supported by RFC 3963 (NEMO Basic Support). Issues are classified according to the Working Group which is the best chartered to solve them. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Classification . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1 (1,1,1): Single MR, Single HA, Single MNP . . . . . . . . 7 2.2 (1,1,n): Single MR, Single HA, Multiple MNPs . . . . . . . 7 2.3 (1,n,1): Single MR, Multiple HAs, Single MNP . . . . . . . 8 2.4 (1,n,n): Single MR, Multiple HAs, Multiple MNPs . . . . . 9 2.5 (n,1,1): Multiple MRs, Single HA, Single MNP . . . . . . . 9 2.6 (n,1,n): Multiple MRs, Single HA, Multiple MNPs . . . . . 10 2.7 (n,n,1): Multiple MRs, Multiple HAs, Single MNP . . . . . 10 2.8 (n,n,n): Multiple MRs, Multiple HAs, Multiple MNPs . . . . 11 3. Deployment Scenarios and Prerequisites . . . . . . . . . . . . 13 3.1 Deployment Scenarios . . . . . . . . . . . . . . . . . . . 13 3.2 Prerequisites . . . . . . . . . . . . . . . . . . . . . . 14 4. Multihoming Issues . . . . . . . . . . . . . . . . . . . . . . 16 4.1 Fault Tolerance . . . . . . . . . . . . . . . . . . . . . 16 4.1.1 Failure Detection . . . . . . . . . . . . . . . . . . 16 4.1.2 Path Exploration . . . . . . . . . . . . . . . . . . . 18 4.1.3 Path Selection . . . . . . . . . . . . . . . . . . . . 19 4.1.4 Re-Homing . . . . . . . . . . . . . . . . . . . . . . 20 4.2 Ingress Filtering . . . . . . . . . . . . . . . . . . . . 21 4.3 Media Detection . . . . . . . . . . . . . . . . . . . . . 22 4.4 HA Synchronization . . . . . . . . . . . . . . . . . . . . 23 4.5 MR Synchronization . . . . . . . . . . . . . . . . . . . . 23 4.6 Prefix Delegation . . . . . . . . . . . . . . . . . . . . 24 4.7 Multiple Bindings/Registrations . . . . . . . . . . . . . 24 4.8 Source Address Selection . . . . . . . . . . . . . . . . . 24 4.9 Loop Prevention in Nested Mobile Networks . . . . . . . . 25 4.10 Prefix Ownership . . . . . . . . . . . . . . . . . . . . . 25 5. Matrix [Issues,(x,y,z) Configuration] . . . . . . . . . . . . 26 6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 27 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 8. Security Considerations . . . . . . . . . . . . . . . . . . . 27 Ng, et al. Expires January 19, 2006 [Page 2] Internet-Draft Analysis of Multihoming in NEMO July 2005 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 10.1 Normative References . . . . . . . . . . . . . . . . . . . 28 10.2 Informative References . . . . . . . . . . . . . . . . . . 28 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 30 A. Alternative Classifications Approach . . . . . . . . . . . . . 32 A.1 Ownership-Oriented Approach . . . . . . . . . . . . . . . 32 A.1.1 ISP Model . . . . . . . . . . . . . . . . . . . . . . 32 A.1.2 Subscriber/Provider Model . . . . . . . . . . . . . . 33 A.2 Problem-Oriented Approach . . . . . . . . . . . . . . . . 35 B. Nested Tunneling for Fault Tolerance . . . . . . . . . . . . . 36 B.1 Detecting Presence of Alternate Routes . . . . . . . . . . 36 B.2 Re-Establishment of Bi-Directional Tunnels . . . . . . . . 36 B.2.1 Using Alternate Egress Interface . . . . . . . . . . . 37 B.2.2 Using Alternate Mobile Router . . . . . . . . . . . . 37 B.3 To Avoid Tunneling Loop . . . . . . . . . . . . . . . . . 38 C. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Intellectual Property and Copyright Statements . . . . . . . . 41 Ng, et al. Expires January 19, 2006 [Page 3] Internet-Draft Analysis of Multihoming in NEMO July 2005 1. Introduction The design goals and objectives of Network Mobility Support (NEMO) in IPv6 are identified in [1] while the terminology is being described in [2] and [3]. NEMO Basic Support (RFC 3963) [4] is the solution proposed by the NEMO Working Group to provide continuous Internet connectivity to nodes located in an IPv6 mobile network, e.g. like in an in-vehicle embedded IP network. The NEMO Basic Support solution basically solves the problem by setting up bi-directional tunnels between the mobile routers (MRs) connecting the mobile network to the Internet and their respective Home Agents (HAs), much how this is done in Mobile IPv6 [5], the solution for host mobility support. NEMO Basic Support is transparent to nodes located behind the mobile router (i.e. the mobile network nodes, or MNNs) and as such doesn't require MNNs to take any action in the mobility management. However, mobile networks are typically connected by means of wireless and thus less reliable links; there could also be many nodes behind the MR. A loss of connectivity or a failure to connect to the Internet has thus a more significant impact than for a single mobile node. Scenarios illustrated in [6] demonstrate that providing a permanent access to mobile networks such as vehicles typically require the use of several interfaces and technologies since the mobile network may be moving in distant geographical locations where different access technologies are provided and governed by distinct access control policies. As specified by R.12 in section 5 of [1], the NEMO WG must ensure that NEMO Basic Support does not prevent mobile networks to be multihomed, i.e. when there is more than one point of attachment between the mobile network and the Internet (see definitions in [3]). This arises either: o when a MR has multiple egress interfaces, or o the mobile network has multiple MRs, or o the mobile network is associated with multiple HAs, or o multiple global prefixes are available in the mobile network. Using NEMO Basic Support, this would translate into having multiple bi-directional tunnels between the MR(s) and the corresponding HA, and may result into multiple MNPs available to the MNNs. However, NEMO Basic Support does not specify any particular mechanism to manage multiple bi-directional tunnels. The objective of this memo is thus multi-folded: Ng, et al. Expires January 19, 2006 [Page 4] Internet-Draft Analysis of Multihoming in NEMO July 2005 o to determine all the potential multihomed configurations for a NEMO, and then to identify which of those may be useful in a real life scenario, o to capture issues that may prevent some multihomed configurations to be supported under the operation of NEMO Basic Support. It doesn't necessarily mean that those not supported will not work with NEMO Basic Support, as it may be up to the implementors to make it work (hopefully this memo will be helpful to these implementors). o to identify potential solutions to the previously identified issues. o to decide which issues are worth to be solved, and to determine which WG should address each of the issues that are worth solving. In order to reach these objectives, a taxonomy to classify the possible multihomed configurations is described in Section 2. Deployment scenarios, their benefits, and requirements to meet these benefits are illustrated in Section 3. Following this, the related issues are studied in Section 4. The issues are then summarized in a matrix for each of the deployment scenario (Section 5). This memo concludes with an evaluation of NEMO Basic Support for multihomed configurations. Alternative classifications are outlined in the Appendix. The readers should note that this document considers multihoming only from the point of view of an IPv6 environment. In order to understand this memo, the reader is expected to be familiar with the above cited documents, i.e. with the NEMO terminology as defined in [2] (section 3) and [3], Goals and Benefits of Multihoming [6], Goals and Requirements of Network Mobility Support [1], and the NEMO Basic Support specification [4]. Goals and benefits of multihoming as discussed in [6] are applicable to fixed nodes, mobile nodes, fixed networks and mobile networks. Ng, et al. Expires January 19, 2006 [Page 5] Internet-Draft Analysis of Multihoming in NEMO July 2005 2. Classification As there are several configurations in which mobile networks are multihomed, there is a need to classify them into a clearly defined taxonomy. This can be done in various ways. A Configuration- Oriented taxonomy is described in this section. Two other taxonomies, namely, the Ownership-Oriented Approach, and the Problem- Oriented Approach are outlined in Appendix A.1 and Appendix A.2. Multihomed configurations can be classified depending on how many mobile routers are present, how many egress interfaces, Care-of Address (CoA) and Home Addresses (HoA) the mobile routers have, how many prefixes (MNPs) are available to the mobile network nodes, etc. We use three key parameters to differentiate the multihomed configurations. Using these parameters, each configuration is referred by the 3-tuple (x,y,z), where 'x', 'y', 'z' are defined as follows: o 'x' indicates the number of MRs where: x=1 implies a mobile network has only a single MR, presumably multihomed. x=n implies a mobile network has more than one MR. o 'y' indicates the number of HAs associated with the entire mobile network, where: y=1 implies that a single HA is assigned to the mobile network. y=n implies that multiple HAs are assigned to the mobile network. o 'z' indicates the number of MNPs available within the NEMO, where: z=1 implies that a single MNP is available in the NEMO. z=N implies that multiple MNPs are available in the NEMO It can be seen that the above three parameters are fairly orthogonal to one another. Thus different values of 'x', 'y' and 'z' give rise to different combinations of the 3-tuple (x,y,z). As described in the sub-sections below, a total of 8 possible configurations can be identified. One thing the reader has to keep in mind is that in each of the following 8 cases, the MR may be multihomed if either (i) multiple prefixes are available (on the home link, or on the visited link), or (ii) the MR is equipped with multiple interfaces. In such a case, the MR would have multiple Home Ng, et al. Expires January 19, 2006 [Page 6] Internet-Draft Analysis of Multihoming in NEMO July 2005 Address / Care-of Address pairs. Issues pertaining to a multihomed MR are also addressed in [7]. In addition, the readers should also keep in mind that when "MNP(s) is/are available in the NEMO", the MNP(s) may either be explicitly announced by the MR via router advertisement, or mad available through Dynamic Host Configuration Protocol (DHCP). 2.1 (1,1,1): Single MR, Single HA, Single MNP The (1,1,1) mobile network has only one MR, it is associated with a single HA, and a single MNP is available in the NEMO. To fall into a multihomed configuration, at least one of the following conditions must hold: o The MR has multiple interfaces, or o Multiple global prefixes are available on the visited link, or o Multiple global prefixes are available on the home link (Note that in this case, those prefixes are not all available in the NEMO, since there is only a single MNP in the NEMO) A bi-directional tunnel would then be established between each pair of Home Address / Care-of Address. Regarding MNNs, they are (usually) not multihomed since they would configure a single global address from the single MNP available on the link they are attached to. _____ _ p _ | | |_|-|<-_ |-|_|-| |-| _ _ |-|_|=| |_____| | _ |-|_| |_|-| | |-|_|-| | MNNs MR AR Internet AR HA Figure 1: (1,1,1): 1 MR, 1 HA, 1 MNP 2.2 (1,1,n): Single MR, Single HA, Multiple MNPs The (1,1,n) mobile network has only one MR, it is associated with a single HA and two or more MNPs are available in the NEMO. The MR may be itself multihomed, as detailed in Section 2.1. In such a case, a bi-directional tunnel would be established between each pair of Home Address / Care-of Address. Ng, et al. Expires January 19, 2006 [Page 7] Internet-Draft Analysis of Multihoming in NEMO July 2005 Regarding MNNs, they are multihomed because several MNPs are available on the link they are attached to. The MNNs would then configure a global address with each MNP available on the link. _____ _ p1,p2 _ | | |_|-|<-_ |-|_|-| |-| _ _ |-|_|=| |_____| | _ |-|_| |_|-| | |-|_|-| | MNNs MR AR Internet AR HA Figure 2: (1,1,n): 1 MR, 1 HA, multiple MNPs 2.3 (1,n,1): Single MR, Multiple HAs, Single MNP The (1,n,1) mobile network has only one MR and a single MNP is available in the NEMO. The MR, however, is associated with multiple HAs, possibly one HA per Home Address, or one HA per egress interface. The NEMO is multihomed since it has multiple HAs, but in addition the conditions detailed in Section 2.1 may also hold for the MR. A bi- directional tunnel would then be established between each pair of Home Address / Care-of Address. Regarding MNNs, they are (usually) not multihomed since they would configure a single global address from the single MNP available on the link they are attached to. AR HA2 _ | |-|_|-| _ _____ | |-|_| _ p _ | |-| |_|-|<-_ |-|_|-| | _ |-|_|=| |_____|-| _ |_|-| | | _ |-|_| |-|_|-| | MNNs MR AR Internet AR HA1 Figure 3: (1,n,1): 1 MR, multiple HAs, 1 MNP Ng, et al. Expires January 19, 2006 [Page 8] Internet-Draft Analysis of Multihoming in NEMO July 2005 2.4 (1,n,n): Single MR, Multiple HAs, Multiple MNPs The (1,n,n) mobile network has only one MR. However, the MR is associated with multiple HAs, possibly one per Home Address (or one HA per egress interface), and more than one MNP is available in the NEMO. The MR is multihomed since it has multiple HAs, but in addition the conditions detailed in Section 2.1 may also hold. A bi-directional tunnel would then be established between each pair of Home Address / Care-of Address. Regarding MNNs, they are generally multihomed since they would configure a global address from each MNP available on the link they are attached to. AR HA2 _ | _ _____ |-|_|-|-|_| _ p1,p2 _ | |-| | |_|-|<-_ |-|_|-| | _ _ |-|_|=| |_____|-| _ |-|_| |_|-| | |-|_|-| | | MNNs MR AR Internet AR HA1 Figure 4: (1,n,n): 1 MR, multiple HAs, multiple MNPs 2.5 (n,1,1): Multiple MRs, Single HA, Single MNP The (n,1,1) mobile network has more than one MR advertising global routes. However, the MR(s) are associated with as single HA, and there in a single MNP available in the NEMO. The NEMO is multihomed since it has multiple MRs, but in addition the conditions detailed in Section 2.1 may also hold for each MR. A bi- directional tunnel would then be established between each pair of Home Address / Care-of Address. Regarding MNNs, they are (usually) not multihomed since they would configure a single global address from the single MNP available on the link they are attached to. Ng, et al. Expires January 19, 2006 [Page 9] Internet-Draft Analysis of Multihoming in NEMO July 2005 MR2 p<-_ | _ |-|_|-| _____ |_|-| |-| | _ | | |-| _ |_|-| _ |-|_____| | _ |-|_| |-|_|-| |-|_|-| p<- | | MNNs MR1 Internet AR HA Figure 5: (n,1,1): Multiple MRs, 1 HA, 1 MNP 2.6 (n,1,n): Multiple MRs, Single HA, Multiple MNPs The (n,1,n) mobile network has more than one MR; multiple global routes are advertised by the MRs and multiple MNPs are available within the NEMO. The NEMO is multihomed since it has multiple MRs, but in addition the conditions detailed in Section 2.1 may also hold for each MR. A bi- directional tunnel would then be established between each pair of Home Address / Care-of Address. Regarding MNNs, they are generally multihomed since they would configure a global address from each MNP available on the link they are attached to. MR2 p2<-_ | _ |-|_|-| _____ |_|-| |-| | _ | | |-| _ |_|-| _ |-|_____| | _ |-|_| |-|_|-| |-|_|-| p1<- | | MNNs MR1 Internet AR HA Figure 6: (n,1,n): Multiple MRs, 1 HA, multiple MNPs 2.7 (n,n,1): Multiple MRs, Multiple HAs, Single MNP The (n,n,1) mobile network has more than one MR advertising multiple global routes. The mobile network is simultaneously associated with multiple HAs and a single MNP is available in the NEMO. The NEMO is multihomed since it has multiple MRs and HAs, but in Ng, et al. Expires January 19, 2006 [Page 10] Internet-Draft Analysis of Multihoming in NEMO July 2005 addition the conditions detailed in Section 2.1 may also hold for each MR. A bi-directional tunnel would then be established between each pair of Home Address / Care-of Address. Regarding MNNs, they are (usually) not multihomed since they would configure a single global address from the single MNP available on the link they are attached to. MR2 AR HA2 p _ | <-_ | |-|_|-| _ _ |-|_|-| _____ | |-|_| |_|-| |-| |-| _ | | | |_|-| _ |-|_____|-| _ |-|_|-| | _ |-|_| <- | |-|_|-| p | MNNs MR1 Internet AR HA1 Figure 7: (n,n,1): Multiple MRs, Multiple HAs, 1 MNP 2.8 (n,n,n): Multiple MRs, Multiple HAs, Multiple MNPs The (n,n,n) mobile network has multiple MRs advertising different global routes. The mobile network is simultaneously associated with more than one HA and multiple MNPs are available in the NEMO. The NEMO is multihomed since it has multiple MRs and HAs, but in addition the conditions detailed in Section 2.1 may also hold for each MR. A bi-directional tunnel would then be established between each pair of Home Address / Care-of Address. Regarding MNNs, they are generally multihomed since they would configure a global address from each MNP available on the link they are attached to. Ng, et al. Expires January 19, 2006 [Page 11] Internet-Draft Analysis of Multihoming in NEMO July 2005 MR2 AR HA2 p2 _ | <-_ | |-|_|-| _ _ |-|_|-| _____ | |-|_| |_|-| |-| |-| _ | | | |_|-| _ |-|_____|-| _ |-|_|-| | _ |-|_| <- | |-|_|-| p1 | MNNs MR1 Internet AR HA1 Figure 8: (n,n,n): Multiple MRs, HAs, and MNPs Ng, et al. Expires January 19, 2006 [Page 12] Internet-Draft Analysis of Multihoming in NEMO July 2005 3. Deployment Scenarios and Prerequisites The following generic goals and benefits of multihoming are discussed in [6]: 1. Permanent and Ubiquitous Access 2. Redundancy/Fault-Recovery 3. Load Sharing 4. Load Balancing 5. Preference Settings These benefits are now illustrated from a NEMO perspective with a typical instance scenario for each case in the taxonomy. We then discuss the prerequisites to fulfill these. 3.1 Deployment Scenarios x=1: Multihomed mobile networks with a single MR o Example: an MR with dual/multiple access interfaces (e.g. 802.11 and GPRS capabilities). This is a S/P-(1,1,*) if both accesses are subscribed to the same ISP. If the two accesses are offered by independent ISPs, this is a S/mP-(1,n,n) [for the meaning of this abbreviation, see Appendix A.1]. Benefits: Ubiquity, Redundancy/Fault-Recovery, Load Sharing, Preference Settings x=N: Multihomed mobile networks with multiple MRs o Example 1: a train with one MR in each car, all served by the same HA, thus a (n,1,*). Alternatively, the train company might be forced to use different ISPs when the train go to different locations, thus it is a (n,n,n). Benefits: Load Sharing, Redundancy/Fault-Recovery, Ubiquity o Example 2: W-PAN with a GPRS-enabled phone and a WiFi-enabled PDA. This is a S/mP-(n,n,n) if the two access technologies are subscribed separately. Benefits: Ubiquity, Redundancy/Fault-Recovery, Preference Settings Ng, et al. Expires January 19, 2006 [Page 13] Internet-Draft Analysis of Multihoming in NEMO July 2005 y=1: Multihomed mobile networks with a single HA o Most single ISP cases in above examples. y=N: Multihomed mobile networks with multiple HAs o Most multiple ISP cases in above examples. o Example: a transatlantic flight with a HA in each continent. This is a (1,n,1) network if there is only one MR. Benefits: Ubiquity, Preferences (reduced delay, shortest path) z=1: Multihomed mobile networks with a single MNP o Most single ISP cases in above examples. z=N: Multihomed mobile networks with multiple MNPs o Most multiple ISP cases in above examples. o Example: a car with a prefix taken from home (personal traffic transit on this prefix and is paid by the owner) and one that belongs to the car manufacturer (maintenance traffic is paid by the car-manufacturer). This will typically be a (1,1,n) or a (1,n,n,). Benefits: Preference Settings 3.2 Prerequisites In this section, requirements are started in order to comply with the expected benefits of multihoming as detailed in [6]. At least one bi-directional tunnel must be available at any point in time between the mobile network and the fixed network to meet all expectations. But for most goals to be effective, multiple tunnels must be maintained simultaneously: o Permanent and Ubiquitous Access: At least one bi-directional tunnel must be available at any point in time. Ng, et al. Expires January 19, 2006 [Page 14] Internet-Draft Analysis of Multihoming in NEMO July 2005 o Redundancy and Fault-Recovery: Both the inbound and outbound traffic must be transmitted or diverted over another bi-directional tunnel once a bi-directional tunnel is broken or disrupted. It should be noted that the provision of fault tolerance capabilities does not necessarily require the existence of multiple bi-directional tunnels simultaneously. o Load Sharing and Load Balancing: Multiple tunnels must be maintained simultaneously. o Preference Settings: Implicitly, multiple tunnels must be maintained simultaneously if preferences are set for deciding which of the available bi- directional tunnels should be used. To allow user/application to set the preference, a mechanism should be provided to the user/ application for the notification of the availability of multiple bi-directional tunnels, and perhaps also to set preferences. Similar mechanism should also be provided to network administrators for the administration of the preferences. Ng, et al. Expires January 19, 2006 [Page 15] Internet-Draft Analysis of Multihoming in NEMO July 2005 4. Multihoming Issues As discussed in the previous section, multiple bi-directional tunnels need to be maintained either simultaneously (e.g. for load sharing) or sequentially (e.g. for fault tolerance) In some cases, it may be necessary to divert packets from a (perhaps failed) bi-directional tunnel to an alternative (perhaps newly established) bi-directional tunnel (i.e. for matters of fault recovery, preferences), or to split traffic between multiple tunnels (load sharing, load balancing). So, depending on the configuration under consideration, the issues discussed below may need to be addressed, sometimes dynamically. For each issue, potential ways to solve the problem are investigated and an a recommendation is made on which IETF WG(s) should look into these issues. 4.1 Fault Tolerance One of the goals of multihoming is the provision of fault tolerance capabilities. In order to provide such features, a set of tasks need to be performed, including: failure detection, alternative available path exploration, path selection, re-homing of established communications. These are also discussed in [8] [9]. In the following sub-sections, we look at these issues in the specific context of NEMO, rather than the general Multi6/Shim6 perspective in [8] [9]. In addition, in some scenarios, it may also be required to provide the mechanisms for coordination between different HAs (see Section 4.4) and also the coordination between different MRs (see Section 4.5). 4.1.1 Failure Detection It is expected for faults to occur more readily at the edge of the network (i.e. the mobile nodes), due to the use of wireless connections. Efficient fault detection mechanisms are necessary to recover in timely fashion. Depending on the NEMO configuration considered, the failure protection domain greatly varies. In some configurations, the protection domain provided by NEMO multihoming is limited to the links between the MR(s) and the HA(s). In other configurations, the protection domain allows to recover from failures in other parts of the path, so an end to end failure detection mechanism is required. Below are detailed which failure detection capabilities are required for each configuration: Ng, et al. Expires January 19, 2006 [Page 16] Internet-Draft Analysis of Multihoming in NEMO July 2005 o For the (1,1,*) cases, multiple paths are available between a single MR and a single HA. All the traffic from and to the NEMO flows through these MR and HA. Failure detection mechanisms need only to be executed between these two devices. This is a NEMO specific issue (MIPv6?). o For the (n,1,*) cases, there is a single HA, so all the traffic from and to the NEMO will flow through it. The failure detection mechanisms need to be able to detect failure in the path between the used MR and the only HA. Hence, the failure detection mechanism needs only to involve the HA and the MRs. This is a NEMO specific issue (MIPv6?). o For the (n,n,*) cases, there are multiple paths between the different HAs and the different MRs. Moreover, the HAs may be located in different networks, and have different Internet access links. This implies that changing the HA used, may not only allow to recover from failures in the link between the HA and the MR but also from other failure modes, affecting other parts of the path. In this case, an end to end failure detection mechanism would provide additional protection. However, a higher number of failures is likely in the link between the HA and the MR, so it may be reasonable to provide optimized failure detection mechanisms for this failure mode even in this scenario, as it is considered next. The (n,n,1) case, however, seems to be pretty NEMO specific, because of the absence of multiple prefixes. The (n,n,n) case is hybrid, since for those cases that selecting a different prefix results in a change of path, the SHIM/multi6 protocols may be useful. The other cases, are NEMO specific. In order for fault recovery to work, the MRs and HAs must first possess a means to detect failures: o On the MR's side, the MR can rely on router advertisements from access routers, or other layer-2 trigger mechanisms to detect faults, e.g. [10], [11], [12] or [13]. (For a related issue, see Section 4.3.) o On the HA's side, it is more difficult to detect tunnel failures. For an ISP deployment model, the HAs and MRs can use proprietary methods (such as constant transmission of heartbeat signals) to detect failures and check tunnel liveness. In the S/P model (see Appendix A.2), a lack of standardized "tunnel liveness" protocol means that it is harder to detect failures. A possible method is for the MRs to send binding updates more regularly with shorter Lifetime values. Similarly, HAs can return binding acknowledgment messages with smaller Lifetime values, thus Ng, et al. Expires January 19, 2006 [Page 17] Internet-Draft Analysis of Multihoming in NEMO July 2005 forcing the MRs to send binding updates more frequently. These binding updates can be used to emulate "tunnel heartbeats". This however may lead to more traffic and processing overhead, since binding updates sent to HAs must be protected (and possibly encrypted) with security associations. 4.1.2 Path Exploration Once a failure in the currently used path is detected, alternative paths need to be explored in order to identify an available one. This process is closely related to failure detection in the sense that paths being explored need to be alternative paths to the one that has failed. There are, however, subtle but significant differences between path exploration and failure detection. Failure detection occurs on the currently used path while path exploration occurs in alternative paths (not in the one currently being used for exchanging packets). Although both path exploration and failure detection are likely to rely on a reachability or keepalive test exchange, failure detection also relies on other information, such as upper layer information (e.g. positive or negative feedback form TCP), lower layer information (e.g. an interface is down), and network layer information (e.g. as an address being deprecated or ICMP error message). Basically, the same cases as in the analysis of the failure detection (Section 4.1.1) issue are identified: o For the (1,1,*) cases, multiple paths are available between a single MR and a single HA. The existing paths between the HA and the MR need to be explored to identify an available one. The mechanism involves only the HA and the MR. This is a NEMO specific issue (MIPv6?). o For the (n,1,*) cases, there is a single HA, so all the traffic from and to the NEMO will flow through it. The available alternative paths are the different ones between the different MRs and the HA. The path exploration mechanism needs only to involve the HA and the MRs. This is a NEMO specific issue (MIPv6?). o For the (n,n,*) cases, there are multiple paths between the different HAs and the different MRs. In this case, alternative paths may be routed completely independently one from each other. In this case, an end to end path exploration mechanism would be able to discover if any of the end to end paths is available. However, a higher number of failures is likely in the link between the HA and the MR, so it may be reasonable to provide optimized path exploration mechanism for this failure mode even in this scenario. The (n,n,1) case, however, seems to be pretty NEMO Ng, et al. Expires January 19, 2006 [Page 18] Internet-Draft Analysis of Multihoming in NEMO July 2005 specific, because of the absence of multiple prefixes. The (n,n,n) case is hybrid, since for those cases that selecting a different prefix result in a change of path, the SHIM/multi6 protocols may be useful. The other cases, are NEMO specific. 4.1.3 Path Selection A path selection mechanism is required to select among the multiple available paths. Depending on the NEMO multihoming configuration involved, the differences between the paths may affect only the part between the HA and the MR or may affect the full end to end path. Related to this, depending on the configuration, path selection may be performed by the HA(s), the MR(s) or the hosts themselves through address selection, as it will be presented next. In the (*,*,1) cases, the multiple available paths mostly differ on the tunnel between the MR and the HA used to carry traffic to/from the NEMO. In this case, path selection is performed by the MR and the intra-NEMO routing system for traffic flowing from the NEMO, and path selection is performed by the HA and intra-Home Network routing system for traffic flowing to the NEMO, as it is presented next. A dynamic path selection mechanism is thus needed so that this path could be selected by: o The HA: it should be able to select the path based on some information recorded in the binding cache. o The MR: it should be able to select the path based on router advertisements received on both its egress interfaces or on its ingress interfaces for the (n,*,*) case. In the (*,*,n) cases, the multiple paths available may differ in more than just the tunnel between the MR and the HA, since the usage of different prefixes may result in using different providers, hence in completely different paths between the involved endpoints. In this case, besides the mechanisms presented in the previous case, additional mechanisms for the end to end path selection may be needed. This mechanism may be closely related to source address selection mechanisms within the hosts, since selecting a given address implies selecting a given prefix, which is associated with a given ISP serving one of the home networks. In this case we need to consider additional mechanisms for path selection based on: Ng, et al. Expires January 19, 2006 [Page 19] Internet-Draft Analysis of Multihoming in NEMO July 2005 o The MNN: it should be able to select the path based on "Default Router Selection" (see [Section 6.3.6. Default Router Selection] [14]) in the (n,*,*) case or based on "Source Address Selection" in the (*,*,n) cases (see Section 4.8 of the present memo). o The user or the application: e.g. in case where a user wants to select a particular access technology among the available technologies for reasons of cost or data rate. o A combination of any of the above: a hybrid mechanism should be also available, e.g. one in which the HA, the MR, and/or the MNNs are coordinated to select the path. When multiple bi-directional tunnels are available and possibly used simultaneously, the mode of operation may be either primary-secondary (one tunnel is precedent over the others and used as the default tunnel, while the other serves as a back-up) or peer-to-peer (no tunnel has precedence over one another, they are used with the same priority). This questions which bi-directional tunnel would be selected, and based on which parameter (e.g. type of flow that goes into/out of the mobile network). The mechanisms for the selection among the different tunnels between the MR(s) and the HA(s) seems to be quite NEMO specific. The mechanisms for selecting among different end to end paths based on address selection are similar to the ones used in other multihoming scenarios, as those considered by Shim6/multi6 (e.g. [15]). 4.1.4 Re-Homing After an outage has been detected and an available alternative path has been identified, a re-homing event takes place, diverting the existent communications from one path to the other. Similar to the previous items involved in this process, the re-homing procedure heavily varies depending on the NEMO multihoming configuration. o For the (*,*,1) configurations, the re-homing procedure involves only the MR(s) and the HA(s). The re-homing procedure may involve the exchange of additional BU messages. These mechanisms are shared between NEMO Basic Support and MIPv6. o For the (*,*,n) cases, in addition to the previous mechanisms, end to end mechanisms may be required. Such mechanisms may involve some form of end to end signaling or may simply rely on using different addresses for the communication. The involved mechanisms may be similar to those required for re- Ng, et al. Expires January 19, 2006 [Page 20] Internet-Draft Analysis of Multihoming in NEMO July 2005 homing Shim6/multi6 communications (e.g. [15]). 4.2 Ingress Filtering Ingress filtering mechanisms [16][17] may drop the outgoing packets when multiple bi-directional tunnels end up at different HAs. This could particularly occur if different MNPs are handled by different home agents. If a packet with a source address configured from a specific MNP is tunnelled to a home agent that does not handle that specific MNP the packet may be discarded either by the home agent or by a border gateway in the home network. The ingress filtering compatibility issue is heavily dependent on the particular NEMO multihoming configuration: o For the (*,*,1) cases, there is not such an issue, since there is a single MNP. o For the (*,1,n) cases, there is not such a problem since there is a single HA, accepting all the MNPs. o (*,n,n) are the cases where the ingress filtering presents some difficulties. In the (1,n,n) case the problem is simplified because all the traffic from and to the NEMO is routed through a single MR. Such configuration allows the MR to properly route packets respecting the constraints imposed by ingress filtering. The more complex case is the (n,n,n) case. A simplified case occurs when all the prefixes are accepted by all the HAs, so that no problems occur with the ingress filtering. However, this cannot be always assumed, resulting in the problem described below. As an example of how this could happen, consider the deployment scenario illustrated in Figure 9. In Figure 9, the mobile network has two mobile routers MR1 and MR2, with home agents HA1 and HA2 respectively. Two bi-directional tunnels are established between the two pairs. Each mobile router advertises a different MNP (P1 and P2). MNP P1 is registered to HA1, and MNP P2 is registered to HA2. Thus, MNNs should be free to auto-configure their addresses on any of P1 or P2. Ingress filtering could thus happen in two cases: o If the two tunnels are available, MNN cannot forward packet with source address equals P1.MNN to MR2. This would cause ingress filtering at HA2 to occur (or even at MR2). This is contrary to normal Neighbor Discovery [14] practice that an IPv6 node is free to choose any router as its default router regardless of the prefix it chooses to use. Ng, et al. Expires January 19, 2006 [Page 21] Internet-Draft Analysis of Multihoming in NEMO July 2005 o If the tunnel to HA1 is broken, packets would be sent through the tunnel to HA1 are diverted through the tunnel to HA2. If HA2 (or some border gateway in the domain of HA2) performs ingress filtering, packets with source address configured from MNP P1 may be discarded. Possible solutions to the ingress filtering incompatibility problem may be based on the following approaches: o Some form of source address dependent routing, whether host-based and/or router-based where the prefix contained in the source address of the packet is considered when deciding which exit router to use when forwarding the packet. o The usage of nested tunnels for (*,n,n) cases. Appendix B describes one such approach. o Deprecating those prefixes associated to non-available exit routers Prefix: P1 +-----+ +----+ +----------+ +-----+ +--| MR1 |--| AR |--| |---| HA1 | | +-----+ +----+ | | +-----+ IP: +-----+ | | | Prefix: P1 P1.MNN or | MNN |--+ | Internet | P2.MNN +-----+ | | | Prefix: P2 | +-----+ +----+ | | +-----+ +--| MR2 |--| AR |--| |---| HA2 | Prefix: P2 +-----+ +----+ +----------+ +-----+ Figure 9: An (n,n,n) mobile network The ingress filtering incompatibilities problems that appear in some NEMO multihoming configurations are similar to those considered in Shim6/multi6. 4.3 Media Detection In order to achieve benefits such as ubiquity or fault recovery, it is necessary for the mobile router to detect the availability of network media. This may be achieved using layer 2 triggers [10], or other mechanism developed/recommended by the Detecting Network Attachment (DNA) Working Group [11][18]. This is related to Section 4.1.1, since the ability to detect media availability would often implies the ability to detect media un- availability. Ng, et al. Expires January 19, 2006 [Page 22] Internet-Draft Analysis of Multihoming in NEMO July 2005 4.4 HA Synchronization In the (*,n,*) mobile networks, a single MNP would be registered at different HAs. This gives rise to the following cases: o Only one HA may actively advertise a route to the MNP, o Multiple HAs at different domains may advertise a route to the same MNP This may pose a problem in the routing infrastructure as a whole if the HAs are located in different administrative domains. The implications of this aspect needs further exploration. Certain level of HA co-ordination may be required. A possible approach is to adopt a HA synchronization mechanism such as that described in [19] and [20]. Such synchronization might also be necessary in a (*,n,*) mobile network, when a MR sends binding update messages to only one HA (instead of all HAs). In such cases, the binding update information might have to be synchronized between HAs. The mode of synchronization may be either primary-secondary or peer-to-peer. In addition, when MNP is delegated to the MR (see Section 4.6), some level of co-ordination between the HAs may also be neceesary. This issue is a general mobility issue that will also have to be dealt with Mobile IPv6. This issue should be dealt within a potentially forthcoming Monami6 WG. 4.5 MR Synchronization In the (n,*,*) mobile network, different MRs may need to be synchronized in order to take common decisions. The mode of synchronization may be either primary-secondary or peer-to-peer. This may include: o In the (n,*,1) case, advertising the same MNP (see also "prefix delegation" in Section 4.6). o In the (n,*,n) case, a MR relaying the advertisement of the MNP from another failed MR. o In the (n,*,*) cases, relaying between MRs everything that needs to be relayed, such as data packets, creating a tunnel from the ingress interface, etc. This problem is general in the sense that a multi-router site in the fixed network would require the same level of router synchronization. It is recommended that the issue be looked at in the IPv6 or Shim6 WG, and the NEMO WG to contribute any NEMO specific requirement. Ng, et al. Expires January 19, 2006 [Page 23] Internet-Draft Analysis of Multihoming in NEMO July 2005 4.6 Prefix Delegation In the (*,*,1) mobile network, the same MNP must be advertised to the MNNs through different paths. This questions how to perform prefix delegation: o For the (*,n,1) mobile network, how multiple HAs would delegate the same MNP to the mobile network. For doing so, the HAs may be somehow configured to advertise the same MNP. (see also "HA Synchronization" in Section 4.4). o For the (n,*,n) mobile network, how multiple mobile routers would be synchronized to advertise the same MNP down the NEMO-link. For doing so, the MRs may be somehow configured to advertise the same MNP (see also "MR Synchronization" in Section 4.5). This could be configured manually, or dynamically. Alternatively, prefix delegation mechanisms [21] [22] could be used to ensure all routers advertise the same MNP. Prefix delegation is currently being explored in the NEMO WG. Should the WG decides to standardize a prefix delegation mechanism, the WG should also consider its application to a multihomed mobile network. 4.7 Multiple Bindings/Registrations When a MR is configured with multiple Care-of Addresses, it is often necessary for it to bind these Care-of Addresses to the same MNP. This is a generic mobility issue, since Mobile IPv6 nodes face a similar problem. This issue is discussed in [7]. It is sufficient to note that solutions like [23] can solve this for both Mobile IPv6 and NEMO Basic Support. This issue should be dealt within a potentially forthcoming Monami6 WG. 4.8 Source Address Selection In the (*,*,n) mobile networks, MNNs would be configured with multiple addresses. Source address selection mechanisms are needed to decide which address to choose from. In addition, source address selection may be closely related to path selection procedures (see Section 4.1.3) and re-homing techniques (see Section 4.1.4). It may be desirable for MNNs to be able to acquire "preference" information on each MNP from the MRs. This would allow default address selection mechanisms such as these specified in [24] to be Ng, et al. Expires January 19, 2006 [Page 24] Internet-Draft Analysis of Multihoming in NEMO July 2005 used. Further exploration on setting such "preference" information in Router Advertisement based on performance of the bi-directional tunnel might prove to be useful. This is a general issue faced by any node when offered multiple prefixes. It is recommended that the issue be examined by other WG (such as IPv6). 4.9 Loop Prevention in Nested Mobile Networks When a multihomed mobile network is nested within another mobile network, it can result in very complex topologies. For instance, a nested mobile network may be attached two different root-MRs, thus the aggregated network no longer forms a simple tree structure. As such, a solution to prevent an infinite loop of multiple mobile routers must be provided. This problem is specific to NEMO Basic Support. It is recommended that the NEMO WG standardizes a solution to solve this problem (such as the use of a tree-spanning algorithm, or [25]). 4.10 Prefix Ownership When a (n,*,1) network splits, (i.e. the two MRs split themselves up), MRs on distinct links may try to register the only available MNP. This cannot be allowed, as the HA has no way to know which node with an address configured from that MNP is attached to which MR. Some mechanism must be present for the MNP to either be forcibly removed from one (or all) MRs, or the implementors must not allow a (n,*,1) network to split. A possible approach to solving this problem is described in [26]. This problem is specific to NEMO Basic Support. It is recommended that the NEMO WG standardizes a solution to solve this problem, or specifies that the split of a (n,*,1) network cannot be allowed without a router renumbering. Ng, et al. Expires January 19, 2006 [Page 25] Internet-Draft Analysis of Multihoming in NEMO July 2005 5. Matrix [Issues,(x,y,z) Configuration] Several issues that might impact the deployment of NEMO with multihoming capabilities were identified in Section 4. These are shown in the matrix below, for each of the eight multihoming configurations, together with indications of the WG(s) in which each issue is the most likely to be solved. +=================================================================+ | # of MRs: | 1 | 1 | 1 | 1 | n | n | n | n | | # of HAs: | 1 | 1 | n | n | 1 | 1 | n | n | | # of Prefixes: | 1 | n | 1 | n | 1 | n | 1 | n | +=================================================================+ | Fault Tolerance | * | * | * | * | * | * | * | * | +---------------------------------+---+---+---+---+---+---+---+---+ | Failure Detection |N/M|N/M|N/M|N/M|N/M|N/M| N | S | +---------------------------------+---+---+---+---+---+---+---+---+ | Path Exploration |N/M|N/M|N/M|N/M|N/M|N/M| N | S | +---------------------------------+---+---+---+---+---+---+---+---+ | Path Selection | N |S/N| N |S/N| N |S/N| N |S/N| +---------------------------------+---+---+---+---+---+---+---+---+ | Re-Homing |N/M| S |N/M| S |N/M| S |N/M| S | +---------------------------------+---+---+---+---+---+---+---+---+ | Ingress Filtering | . | . | . | t | . | . | . | N | +---------------------------------+---+---+---+---+---+---+---+---+ | Media Detection | D | D | D | D | D | D | D | D | +---------------------------------+---+---+---+---+---+---+---+---+ | HA Synchronization | . | . |N/M|N/M| . | . |N/M|N/M| +---------------------------------+---+---+---+---+---+---+---+---+ | MR Synchronization | . | . | . | . | G | G | G | G | +---------------------------------+---+---+---+---+---+---+---+---+ | Prefix Delegation | . | . | N | N | N | N | N | N | +---------------------------------+---+---+---+---+---+---+---+---+ | Multiple Binding/Registrations | M | M | M | M | M | M | M | M | +---------------------------------+---+---+---+---+---+---+---+---+ | Source Address Selection | . | G | . | G | . | G | . | G | +---------------------------------+---+---+---+---+---+---+---+---+ | Loop Prevention in Nested NEMO | N | N | N | N | N | N | N | N | +---------------------------------+---+---+---+---+---+---+---+---+ | Prefix Ownership | . | . | . | . | N | . | N | . | +=================================================================+ N - NEMO Specific M - MIPv6 Specific G - Generic IPv6 S - SHIM6 WG D - DNA WG . - Not an Issue t - trivial * - Fault Tolerance is a combination of Failure Detection, Path Exploration, Path Selection, and Re-Homing Ng, et al. Expires January 19, 2006 [Page 26] Internet-Draft Analysis of Multihoming in NEMO July 2005 6. Conclusion This memo is an analysis of multihoming in the context of network mobility under the operation of NEMO Basic Support. The purpose of this memo is to investigate issues related to such a bi-directional tunneling mechanism when mobile networks are multihomed. For doing so, a taxonomy was proposed to classify the mobile networks in eight possible multihomed configurations. The issue were explained and were then summarized in a table showing under which multihoming configuration it applies, and which IETF working group is the best chartered to solve it. This analysis will be helpful to extend the existing standards to support multihoming and to implementors of NEMO Basic Support and multihoming-related mechanisms. 7. IANA Considerations This is an informational document and does not require any IANA action. 8. Security Considerations This is an informational document where the multihoming configurations under the operation of NEMO Basic Support are analyzed. Security considerations of these multihoming configurations, should they be different from those that concern NEMO Basic Support, must be considered by forthcoming solutions. 9. Acknowledgments The authors would like to thank people who have given valuable comments on various multihoming issues on the mailing list, and also those who have suggested directions in the 56th - 61st IETF Meetings. The initial evaluation of NEMO Basic Support is a contribution from Julien Charbon. Ng, et al. Expires January 19, 2006 [Page 27] Internet-Draft Analysis of Multihoming in NEMO July 2005 10. References 10.1 Normative References [1] Ernst, T., "Network Mobility Support Goals and Requirements", draft-ietf-nemo-requirements-04 (work in progress), February 2005. [2] Manner, J. and M. Kojo, "Mobility Related Terminology", RFC 3753, June 2004. [3] Ernst, T. and H. Lach, "Network Mobility Support Terminology", draft-ietf-nemo-terminology-03 (work in progress), February 2005. [4] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert, "Network Mobility (NEMO) Basic Support Protocol", RFC 3963, January 2005. [5] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. 10.2 Informative References [6] Ernst, T., "Goals and Benefits of Multihoming", draft-multihoming-generic-goals-and-benefits-00 (work in progress), February 2004. [7] Montavont, N., Wakikawa, R., Ernst, T., Ng, C., and K. Kuladinithi, "Analysis of Multihoming in Mobile IPv6", draft-montavont-mobileip-multihoming-pb-statement-04 (work in progress), June 2005. [8] Arkko, J., "Failure Detection and Locator Selection Design Considerations", draft-ietf-shim6-failure-detection-00 (work in progress), July 2005. [9] Beijnum, I., "Shim6 Reachability Detection", draft-ietf-shim6-reach-detect-00 (work in progress), July 2005. [10] Yegin, A., "Link-layer Event Notifications for Detecting Network Attachments", draft-ietf-dna-link-information-01 (work in progress), February 2005. [11] Narayanan, S., "Detecting Network Attachment in IPv6 - Best Current Practices for hosts.", draft-ietf-dna-hosts-00 (work in progress), April 2005. Ng, et al. Expires January 19, 2006 [Page 28] Internet-Draft Analysis of Multihoming in NEMO July 2005 [12] Yegin, A., "Link-layer Hints for Detecting Network Attachments", draft-yegin-dna-l2-hints-01 (work in progress), February 2004. [13] Yegin, A., "Supporting Optimized Handover for IP Mobility -Requirements for Underlying Systems", draft-manyfolks-l2-mobilereq-02 (work in progress), July 2002. [14] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. [15] Bagnulo, M. and J. Arkko, "Functional decomposition of the multihoming protocol", draft-ietf-shim6-functional-dec-00 (work in progress), July 2005. [16] Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, May 2000. [17] Baker, F. and P. Savola, "Ingress Filtering for Multihomed Networks", BCP 84, RFC 3704, March 2004. [18] Narayanan, S., "Detecting Network Attachment in IPv6 - Best Current Practices for Routers", draft-ietf-dna-routers-00 (work in progress), July 2005. [19] Wakikawa, R., Devarapalli, V., and P. Thubert, "Inter Home Agents Protocol (HAHA)", draft-wakikawa-mip6-nemo-haha-01 (work in progress), February 2004. [20] Koh, B., Ng, C., and J. Hirano, "Dynamic Inter Home Agent Protocol", draft-koh-mip6-nemo-dhap-00 (work in progress), July 2004. [21] Miyakawa, S. and R. Droms, "Requirements for IPv6 Prefix Delegation", RFC 3769, June 2004. [22] Droms, R. and P. Thubert, "DHCPv6 Prefix Delegation for NEMO", draft-droms-nemo-dhcpv6-pd-02 (work in progress), April 2005. [23] Wakikawa, R., Uehara, K., Ernst, T., and K. Nagami, "Multiple Care-of Addresses Registration", draft-wakikawa-mobileip-multiplecoa-04 (work in progress), June 2005. [24] Draves, R., "Default Address Selection for Internet Protocol version 6 (IPv6)", RFC 3484, February 2003. Ng, et al. Expires January 19, 2006 [Page 29] Internet-Draft Analysis of Multihoming in NEMO July 2005 [25] Thubert, P., "Nested Nemo Tree Discovery", draft-thubert-tree-discovery-02 (work in progress), July 2005. [26] Kumazawa, M., "Token based Duplicate Network Detection for split mobile network (Token based DND)", draft-kumazawa-nemo-tbdnd-02 (work in progress), July 2005. [27] Choi, S., "Threat for Multi-homed Mobile Networks", draft-cho-nemo-threat-multihoming-00 (work in progress), February 2004. [28] Montavont, N., Noel, T., and M. Kassi-Lahlou, "MIPv6 for Multiple Interfaces", draft-montavont-mobileip-mmi-00 (work in progress), July 2002. [29] Draves, R. and D. Thaler, "Default Router Preferences and More- Specific Routes", draft-ietf-ipv6-router-selection-07 (work in progress), January 2005. 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 Eun Kyoung Paik KT Portable Internet Team, Convergence Lab., KT 17 Woomyeon-dong, Seocho-gu Seoul 137-792 Korea Phone: +82-2-526-5233 Fax: +82-2-526-5200 Email: euna@kt.co.kr URI: http://mmlab.snu.ac.kr/~eun/ Ng, et al. Expires January 19, 2006 [Page 30] Internet-Draft Analysis of Multihoming in NEMO July 2005 Thierry Ernst WIDE at Keio University Jun Murai Lab., Keio University. K-square Town Campus, 1488-8 Ogura, Saiwa-Ku Kawasaki, Kanagawa 212-0054 Japan Phone: +81-44-580-1600 Fax: +81-44-580-1437 Email: ernst@sfc.wide.ad.jp URI: http://www.sfc.wide.ad.jp/~ernst/ Marcelo Bagnulo Universidad Carlos III de Madrid Av. Universidad, 30 Leganes, Madrid 28911 Spain Phone: +34 91624 8837 Email: marcelo@it.uc3m.es Ng, et al. Expires January 19, 2006 [Page 31] Internet-Draft Analysis of Multihoming in NEMO July 2005 Appendix A. Alternative Classifications Approach A.1 Ownership-Oriented Approach An alternative approach to classifying multihomed mobile network is proposed by Erik Nordmark (Sun Microsystems) by breaking the classification of multihomed network based on ownership. This is more of a tree-like top-down classification. Starting from the control and ownership of the HA(s) and MR(s), there are two different possibilities: either (i) the HA(s) and MR(s) are controlled by a single entity, or (ii) the HA(s) and MR(s) are controlled by separate entities. We called the first possibility the 'ISP Model', and the second the 'Subscriber/Provider Model'. A.1.1 ISP Model The case of the HA(s) and MR(s) are controlled by the same entity can be best illustrated as an Internet Service Provider (ISP) installing mobile routers on trains, ships or planes. It is up to the ISP to deploy a certain configuration of mobile network; all 8 configurations as described in the Configuration-Oriented Approach are possible. In the remaining portion of this document, when specifically referring to a mobile network configuration that is controlled by a single entity, we will add an 'ISP' prefix: for example: ISP-(1,1,1) or ISP-(1,N,N). When the HA(s) and MR(s) are controlled by a single entity (such as an ISP), the ISP can decide whether it wants to assign one or multiple MNPs to the mobile network just like it can make the same decision for any other link in its network (wired or otherwise). In any case, the ISP will make the routing between the mobile networks and its core routers (such as the HAs) work. This include not introducing any aggregation between the HAs which will filter out routing announcements for the MNP(es). To such ends, the ISP has various means and mechanisms. For one, the ISP can run its Interior Gateway Protocol (IGP) over bi-directional tunnels between the MR(s) and HA(s). Alternatively, static routes may be used with the tunnels. When static routes are used, a mechanism to test "tunnel liveness" might be necessary to avoid maintaining stale routes. Such "tunnel liveness" may be tested by sending heartbeats signals from MR(s) to the HA(s). A possibility is to simulate heartbeats using Binding Updates messages by controlling the "Lifetime" field of the Binding Acknowledgment message to force the MR to send Binding Update messages at regular interval. However, a more appropriate tool might be the Binding Refresh Request message, though conformance to the Binding Refresh Request message may be less strictly enforced in implementations since it serves a somewhat Ng, et al. Expires January 19, 2006 [Page 32] Internet-Draft Analysis of Multihoming in NEMO July 2005 secondary role when compared to Binding Update messages. A.1.2 Subscriber/Provider Model The case of the HA(s) and MR(s) are controlled by the separate entities can be best illustrated with a subscriber/provider model, where the MRs belongs to a single subscriber and subscribes to one or more ISPs for HA services. There is two sub-categories in this case: when the subscriber subscribes to a single ISP, and when the subscriber subscribes to multiple ISPs. In the remaining portion of this document, when specifically referring to a mobile network configuration that is in the subscriber/provider model where the subscriber subscribes to only one ISP, we will add an 'S/P' prefix: for example: S/P-(1,1,1) or S/P-(1,n,n). When specifically referring to a mobile network configuration that is in the subscriber/provider model where the subscriber subscribes to multiple ISPs, we will add an 'S/mP' prefix: for example: S/mP-(1,1,1) or S/mP-(1,n,n). Not all 8 configurations are likely to be deployed for the S/P and S/mP models. For instance, it is unlikely to foresee a S/mP-(*,1,1) mobile network where there is only a single HA. For the S/P model, the following configurations are likely to be deployed: o S/P-(1,1,1): Single Provider, Single MR, Single HA, Single MNP o S/P-(1,1,n): Single Provider, Single MR, Single HA, Multiple MNPs o S/P-(1,n,1): Single Provider, Single MR, Multiple HAs, Single MNP o S/P-(1,n,n): Single Provider, Single MR, Multiple HAs, Multiple MNPs o S/P-(n,n,1): Single Provider, Multiple MRs, Single HA, Single MNP o S/P-(n,1,n): Single Provider, Multiple MRs, Single HA, Multiple MNPs o S/P-(n,n,1): Single Provider, Multiple MRs, Multiple HAs, Single MNP o S/P-(n,n,n): Single Provider, Multiple MRs, Multiple HAs, Multiple MNPs For the S/mP model, the following configurations are likely to be deployed: Ng, et al. Expires January 19, 2006 [Page 33] Internet-Draft Analysis of Multihoming in NEMO July 2005 o S/mP-(1,n,1): Multiple Providers, Single MR, Multiple HAs, Single MNP o S/mP-(1,n,n): Multiple Providers, Single MR, Multiple HAs, Multiple MNPs o S/mP-(n,n,n): Multiple Providers, Multiple MRs, Multiple HAs, Multiple MNPs When the HA(s) and MR(s) are controlled by different entities, it is more likely the scenario where the MR is controlled by one entity (i.e. the subscriber), and the MR is establishing multiple bi- directional tunnels to one or more HA(s) provided by one or more ISP(s). In such case, it is unlikely for the ISP to run IGP over the bi-directional tunnel, since ISP would most certainly wish to retain full control of its routing domain. Ng, et al. Expires January 19, 2006 [Page 34] Internet-Draft Analysis of Multihoming in NEMO July 2005 A.2 Problem-Oriented Approach A third approach is proposed by Pascal Thubert (Cisco System). This focused on the problems of multihomed mobile networks rather than the configuration or ownership. With this approach, there is a set of 4 categories based on two orthogonal parameters: the number of HAs, and the number of MNPs advertised. Since the two parameters are orthogonal, the categories are not mutually exclusive. The four categories are: o Tarzan: Single HA for Different Care-of Addresses of Same MNP This is the case where one mobile router registers different Care-of Addresses to the same home agent for the same subnet prefix. This is equivalent to the case of y=1, i.e. the (1,1,*) mobile network. o JetSet: Multiple HAs for Different Care-of Addresses of Same MNP This is the case where the mobile router registers different Care-of Addresses to different home agents for the same subnet prefix. This is equivalent to the case of y=n, i.e. the (1,n,*) mobile network. o Shinkansen: Single MNP Advertised by MR(s) This is the case where one MNP is announced by different MRs. This is equivalent to the case of x=n and z=1, i.e. the (n,*,1) mobile network. o DoubleBed: Multiple MNPs Advertised by MR(s) This is the case where more than one MNPs are announced by the different MRs. This is equivalent to the case of x=n and z=n, i.e. the (n,*,n) mobile network. Ng, et al. Expires January 19, 2006 [Page 35] Internet-Draft Analysis of Multihoming in NEMO July 2005 Appendix B. Nested Tunneling for Fault Tolerance In order to utilize the additional robustness provided by multihoming, MRs that employ bi-directional tunneling with their HAs should dynamically change their tunnel exit points depending on the link status. For instance, if a MR detects that one of its egress interface is down, it should detect if any other alternate route to the global Internet exists. This alternate route may be provided by any other MRs connected to one of its ingress interfaces that has an independent route to the global Internet, or by another active egress interface the MR itself possess. If such an alternate route exists, the MR should re-establish the bi-directional tunnel using this alternate route. In the remaining part of this section, we will attempt to investigate methods of performing such re-establishment of bi-directional tunnels. This method of tunnel re-estblishment is particularly useful for the (*,n,n) NEMO configuration. It is not the objective of this memo to specify a new protocol specifically tailored to provide this form of re- establishments. Instead, we will limit ourselves to currently available mechanisms specified in Mobile IPv6 [5] and Neighbor Discovery in IPv6 [14]. B.1 Detecting Presence of Alternate Routes To actively utilize the robustness provided by multihoming, a MR must first be capable of detecting alternate routes. This can be manually configured into the MR by the administrators if the configuration of the mobile network is relatively static. It is however highly desirable for MRs to be able to discover alternate routes automatically for greater flexibility. The case where a MR possesses multiple egress interface (bound to the same HA or otherwise) should be trivial, since the MR should be able to "realize" it has multiple routes to the global Internet. In the case where multiple MRs are on the mobile network, each MR has to detect the presence of other MR. A MR can do so by listening for Router Advertisement message on its *ingress* interfaces. When a MR receives a Router Advertisement message with a non-zero Router Lifetime field from one of its ingress interfaces, it knows that another MR which can provide an alternate route to the global Internet is present in the mobile network. B.2 Re-Establishment of Bi-Directional Tunnels When a MR detects that the link by which its current bi-directional tunnel with its HA is using is down, it needs to re-establish the bi- Ng, et al. Expires January 19, 2006 [Page 36] Internet-Draft Analysis of Multihoming in NEMO July 2005 directional tunnel using an alternate route detected. We consider two separate cases here: firstly, the alternate route is provided by another egress interface that belongs to the MR; secondly, the alternate route is provided by another MR connected to the mobile network. We refer to the former case as an alternate route provided by an alternate egress interface, and the latter case as an alternate route provided by an alternate MR. B.2.1 Using Alternate Egress Interface When an egress interface of a MR loses the connection to the global Internet, the MR can make use of its alternate egress interface should it possess multiple egress interfaces. The most direct way to do so is for the mobile router to send a binding update to the home agent of the failed interface using the Care-of Address assigned to the alternate interface in order to re-establish the bi-directional tunneling using the Care-of Address on the alternate egress interface. After a successful binding update, the MR encapsulates outgoing packets through the bi-directional tunnel using the alternate egress interface. The idea is to use the global address (most likely a Care-of Address) assigned to an alternate egress interface as the new (back-up) Care-of Address of the mobile router to re-establish the bi- directional tunneling with its home agent. B.2.2 Using Alternate Mobile Router When the MR loses a connection to the global Internet, the MR can utilize a route provided by an alternate MR (if one exists) to re- establish the bi-directional tunnel with its HA. First, the MR has to obtain a Care-of Address from the alternate MR (i.e. attaches itself to the alternate MR). Next, it sends binding update to its HA using the Care-of Address obtained from the alternate MR. From then on, the MR can encapsulates outgoing packets through the bi- directional tunnel using via the alternate MR. The idea is to obtain a Care-of Address from the alternate MR and use this as the new (back-up) Care-of Address of the MR to re-establish the bi-directional tunneling with its HA. Note that every packet sent between MNNs and their correspondent nodes will experience two levels of encapsulation. First level of tunneling occurs between a MR which the MNN uses as its default router and the MR's HA. The second level of tunneling occurs between the alternate MR and its HA. Ng, et al. Expires January 19, 2006 [Page 37] Internet-Draft Analysis of Multihoming in NEMO July 2005 B.3 To Avoid Tunneling Loop The method of re-establishing the bi-directional tunnel as described in Appendix B.2 may lead to infinite loops of tunneling. This happens when two MRs on a mobile network lose connection to the global Internet at the same time and each MR tries to re-establish bi-directional tunnel using the other MR. We refer to this phenomenon as tunneling loop. One approach to avoid tunneling loop is for a MR that has lost connection to the global Internet to insert an option into the Router Advertisement message it broadcasts periodically. This option serves to notify other MRs on the link that the sender no longer provides global connection. Note that setting a zero Router Lifetime field will not work well since it will cause MNNs that are attached to the MR to stop using the MR as their default router too (in which case, things are back to square one). Ng, et al. Expires January 19, 2006 [Page 38] Internet-Draft Analysis of Multihoming in NEMO July 2005 Appendix C. Change Log o This draft is an update of draft-ng-nemo-multihoming-issues-03.txt which is itself a merge of 3 previous drafts draft-ng-nemo-multihoming-issues-02.txt, draft-eun-nemo-multihoming-problem-statement-00.txt, and draft-charbon-nemo-multihoming-evaluation-00.txt o Changes from draft-ietf-nemo-multihoming-issues-02 to -03: * Enlisted Marcelo Bagnulo as co-author * Restructuring of Section 4: + Re-named 'Path Survival' to 'Fault Tolerance' + Moved 'Path Failure Detection' and 'Path Selection' as sub- issues of 'Fault Tolerance' + Added 'Path Exploration' and 'Re-homing' as sub-issues of 'Fault Tolerance' + Removed 'Impact on Routing Infrastructure' * Breaking references into Normative and Informative o Changes from draft-ietf-nemo-multihoming-issues-01 to -02: * Added recommendations/suggestion of which WG each issue should be addressed as pointed out in 61st IETF. * Minor updates on references. o Changes from draft-ietf-nemo-multihoming-issues-00 to -01: * Replaced NEMO-Prefix with MNP as decided by the WG at 60th IETF * Addressed Issue #1 in Section 1: Added a note to remind readers that IPv6 is implicitly assumed * Addressed Issue #3 in Section 2.3: Removed text on assumption * Addressed Issue #6 in Section 3.1: Added benefits * Addressed Issue #7 in Section 3.2: Modified text * Addressed Issue #9 in Section 4.2: Modified text Ng, et al. Expires January 19, 2006 [Page 39] Internet-Draft Analysis of Multihoming in NEMO July 2005 * Addressed Issue #10 in Section 4.1.1: Added paragraph on other failure modes * Addressed Issue #10: New Section 4.3 on media detection * Addressed Issue #11 in Section 4.11: modified text o Changes from draft-ng-multihoming-issues-03 to draft-ietf-nemo-multihoming-issues-00: * Expanded "Problem Statement" (Section 4) * Merged "Evaluation" Section into "Problem Statement" (Section 4) * Cleaned up description in "Classification" (Section 2), and clearly indicate in each classification, what are the multihomed entities * Re-organized "Deployment Scenarios and Prerequisites" (Section 3), and created the "Prerequisites" sub-section. o Changes from draft-ng-multihoming-issues-02 to draft-ng-multihoming-issues-03: * Merged with draft-eun-nemo-multihoming-problem-statement (see "Problem Statement" (Section 4)) * Included conclusions from draft-charbon-nemo-multihoming-evaluation-00 * Re-organized some part of "Benefits/Issues of Multihoming in NEMO" to "Problem Statement" (Section 4) * Removed lots of text to be in sync with [6]. * Title changed from "Multihoming Issues in NEMO Basic Support" to "Analysis of Multihoming in NEMO" * Changed (w,x,y) to (x,y,z) in taxonomy. * Moved alternative approaches of classification to Appendix * Creation of this Change-Log itself ;-) Ng, et al. Expires January 19, 2006 [Page 40] Internet-Draft Analysis of Multihoming in NEMO July 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Ng, et al. Expires January 19, 2006 [Page 41]