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diff --git a/doc/rfc/rfc5563.txt b/doc/rfc/rfc5563.txt new file mode 100644 index 0000000..7095be4 --- /dev/null +++ b/doc/rfc/rfc5563.txt @@ -0,0 +1,2299 @@ + + + + + + +Independent Submission K. Leung +Request for Comments: 5563 G. Dommety +Category: Informational Cisco Systems +ISSN: 2070-1721 P. Yegani + Juniper Networks + K. Chowdhury + Starent Networks + February 2010 + + + WiMAX Forum / 3GPP2 Proxy Mobile IPv4 + +Abstract + + Mobile IPv4 is a standard mobility protocol that enables an IPv4 + device to move among networks while maintaining its IP address. The + mobile device has the Mobile IPv4 client function to signal its + location to the routing anchor, known as the Home Agent. However, + there are many IPv4 devices without such capability due to various + reasons. This document describes Proxy Mobile IPv4 (PMIPv4), a + scheme based on having the Mobile IPv4 client function in a network + entity to provide mobility support for an unaltered and mobility- + unaware IPv4 device. This document also describes a particular + application of PMIPv4 as specified in the WiMAX Forum and another + application that is to be adopted in 3GPP2. + +Status of This Memo + + This document is not an Internet Standards Track specification; it is + published for informational purposes. + + This is a contribution to the RFC Series, independently of any other + RFC stream. The RFC Editor has chosen to publish this document at + its discretion and makes no statement about its value for + implementation or deployment. Documents approved for publication by + the RFC Editor are not a candidate for any level of Internet + Standard; see Section 2 of RFC 5741. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + http://www.rfc-editor.org/info/rfc5563. + + + + + + + + + + +Leung, et al. Informational [Page 1] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +Copyright Notice + + Copyright (c) 2010 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents + (http://trustee.ietf.org/license-info) in effect on the date of + publication of this document. Please review these documents + carefully, as they describe your rights and restrictions with respect + to this document. + +Table of Contents + + 1. Introduction ....................................................3 + 2. Conventions Used in This Document ...............................4 + 3. Benefits of Proxy Mobile IPv4 ...................................6 + 4. Overview of Proxy Mobile IPv4 ...................................7 + 4.1. Mobility Signaling for Mobile Device .......................7 + 4.1.1. Proxy Registration during Initial Network + Attachment ..........................................8 + 4.1.2. Proxy Registration Renewal .........................11 + 4.1.3. Proxy Handover Support .............................12 + 4.1.4. Resource Cleanup ...................................13 + 4.2. Establishment of a Bi-Directional Tunnel ..................14 + 4.2.1. Packet Forwarding ..................................14 + 4.2.2. Broadcast and Multicast ............................14 + 4.2.3. Forwarding between Devices on the Same PMA .........15 + 4.3. Security Association between the PMA and the HA ...........15 + 4.4. Registration Sequencing ...................................15 + 4.5. Mobile Device Interface Configuration .....................16 + 4.6. Dynamic HA Discovery ......................................16 + 5. Proxy Mobile IPv4 Extensions ...................................16 + 5.1. PMIPv4 Per-Node Authentication Method Extension ...........17 + 5.2. Proxy Mobile IPv4 Interface ID Extension ..................18 + 5.3. Proxy Mobile IPv4 Device ID Extension .....................18 + 5.4. Proxy Mobile IPv4 Subscriber ID Extension .................19 + 5.5. PMIPv4 Access Technology Type Extension ...................20 + 6. Appearance of Being at Home Network ............................22 + 6.1. ARP Considerations ........................................22 + 6.2. ICMP Considerations .......................................23 + 6.3. DHCP Considerations .......................................23 + 6.4. PPP IPCP Considerations ...................................24 + 6.5. Link-Local Multicast and Broadcast Considerations .........24 + 7. Proxy Mobility Agent Operation .................................24 + 8. Home Agent Operation ...........................................25 + 8.1. Processing Proxy Registration Requests ....................26 + + + + +Leung, et al. Informational [Page 2] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + 9. Mobile Device Operation ........................................26 + 9.1. Initial Network Access ....................................27 + 9.2. Mobile Device Mobility ....................................27 + 9.3. Sending and Receiving Packets .............................27 + 10. Proxy Mobile IPv4 Use Case in WiMAX ...........................28 + 10.1. Proxy Mobile IPv4 Call Flow Examples with Split + PMA in WiMAX .............................................31 + 11. Proxy Mobile IPv4 Use Case in 3GPP2 ...........................33 + 11.1. Handover Considerations in 3GPP2 .........................36 + 12. IANA Considerations ...........................................37 + 12.1. Mobile IPv4 Extension Types ..............................38 + 12.2. Mobile IPv4 Error Codes ..................................38 + 13. Security Considerations .......................................38 + 14. Acknowledgements ..............................................38 + 15. References ....................................................39 + 15.1. Normative References .....................................39 + 15.2. Informative References ...................................39 + +1. Introduction + + There are many IPv4 devices that do not have or cannot be enabled + with Mobile IPv4 [RFC3344] functionality. Yet, mobility for them is + essential. Proxy Mobile IPv4 provides mobility support without + "touching" these devices. The scheme is based on network entities + that perform the mobility-management function for a mobile device. + The location of the device is signaled by the network element on the + access network (referred to as the Proxy Mobility Agent (PMA)) to + inform the network entity on the home network (referred to as the + Home Agent (HA)) associated with the IPv4 address used by the device. + Mobile IPv4 messaging is used by the PMA and HA, which correspond to + the RFC 3344 entities Mobile Node (in proxy mode) and Home Agent, + respectively. + + These are some examples of Proxy Mobile IPv4: + + 1. A Wireless Local Area Network (WLAN) access point or cellular + base station performs registration with the Home Agent when a + mobile device is associated on the air-link. + + 2. An access router or Foreign Agent performs registration with the + Home Agent when a mobile device is detected on the network. + + Mobile IPv4 is used by the network entities because the mobility + protocol has the functions needed to set up the route and tunneling + endpoints for the mobile device's IP address and to deliver + configuration parameters (e.g., DNS server addresses, default + gateway) for enabling the mobile device's IP stack. When Mobile IPv4 + is used in this way, the security association is between the PMA and + + + +Leung, et al. Informational [Page 3] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + the HA because these entities are the signaling endpoints. Also, + when the mobile device moves to a new PMA, the sequencing of messages + sourced from multiple PMAs needs to be handled properly by the HA. + + This document describes how the network entities, PMA and HA, provide + mobility management for the mobile device. It is organized to cover + the generic functionality of Proxy Mobile IPv4 and also the specifics + pertaining to WiMAX (Section 10) and 3GPP2 (Section 11). + + Note that Proxy Mobile IPv6 [RFC5213] is an IETF standard for + network-based mobility management that enables IP mobility for a host + without requiring its participation in any mobility-related + signaling. + +2. Conventions Used in This Document + + The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [RFC2119]. + + The following new terminology and abbreviations are introduced in + this document; all other general mobility-related terms are as + defined in Mobile IPv4 specification [RFC3344]. + + Mobile Device + + The mobile device is used to refer to an IPv4 device with its + mobility provided by the network. The mobile device is not + required to participate in any mobility-related signaling for + achieving mobility for an obtained IP address. + + Proxy Mobile IPv4 Client (PMIPv4 Client) + + This network function is responsible for initiating and + maintaining the Proxy Mobile IPv4 registration on behalf of the + mobile device. Essentially, it performs the Mobile IPv4 client + function but is hosted in the network. In some cases, this + function is collocated with the Foreign Agent; in others, it is + not. In both cases, Proxy Mobile IPv4 registration still goes via + the Foreign Agent at all practical effects, even if it is internal + to the node. + + Home Agent (HA) + + The Home Agent that is defined in Mobile IPv4 [RFC3344] is used in + the Proxy Mobile IPv4 scheme. It is the topological anchor point + for the mobile device's home network and is the entity that + manages the mobile device's reachability state. The additional + + + +Leung, et al. Informational [Page 4] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + capabilities for supporting Proxy Mobile IPv4 in the Home Agent + are defined in this document. + + Foreign Agent (FA) + + The Foreign Agent that is defined in [RFC3344] is used in the + Proxy Mobile IPv4 scheme. It is either collocated with or + separate from the PMIPv4 client. It serves the purpose of tunnel + endpoint from Proxy Mobile IPv4 perspective. + + Access Router (AR) + + Access Router is a commonly used term that refers to the node in + the network that connects the hosts to the IP network. + + Proxy Mobility Agent (PMA) + + Proxy Mobility Agent is the logical entity in the network that + encompasses both the PMIPv4 client and the FA functions. The + PMIPv4 client and the FA collocation in the Access Router + constitute an integrated PMA. When the PMIPv4 client and the FA + functions are not collocated in the Access Router, it is referred + to as a split PMA. A PMIPv4 client may have association with + multiple FAs, and vice versa. + + Proxy Registration Request (PRRQ) + + The Registration Request message is sent by the Proxy Mobility + Agent to the Home Agent in order to set up a mobility binding + entry for a mobile device. The message format is identical to + that of the Mobile IPv4 Registration Request, though the Proxy + Mobile IPv4 extensions that are defined in this document may be + included for enhanced features of network-based mobility + management. + + Proxy Registration Reply (PRRP) + + The Registration Reply message is sent by the Home Agent in + response to the Proxy Registration Request received from the Proxy + Mobility Agent. The message format is identical to that of the + Mobile IPv4 Registration Reply, though the Proxy Mobile IPv4 + extensions that are defined in this document may be included for + enhanced features of network-based mobility management. + + + + + + + + +Leung, et al. Informational [Page 5] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +3. Benefits of Proxy Mobile IPv4 + + Proxy Mobile IPv4 (PMIPv4) is designed to satisfy the requirements + listed below. In addition, while this specification and Proxy Mobile + IPv4 are not standards, they employ a standard: Mobile IPv4. + Implementations of Mobile IPv4 can be re-used (i.e., a client-based + mobility protocol can be used "as-is" to support network-based + mobility). However, new PMIPv4 extensions that are added to Mobile + IPv4 improves the flexibility of the solution. The practical + advantage of having a common mobility protocol for both client-based + and network-based mobility is that a Home Agent can anchor all types + of mobile devices, both ones that have and ones that lack the Mobile + IPv4 function. + + The network-based mobility management solution defined in this + document has the following significant reasons for its use in any + wireless network: + + 1. Support for Unmodified Hosts + + An overwhelming majority of IPv4 hosts do not have Mobile IPv4 + capability. Providing mobility for them is achievable using + Proxy Mobile IPv4. This is accomplished without "touching" the + user's devices by running on a myriad of operating systems and + networking stacks. + + 2. Re-Use of Existing Home Agent + + An existing Home Agent implementation can be used for network- + based mobility as well. Further enhancements are optional and + only incremental in nature. There are many commonalities between + client-based and network-based mobility, and sharing the same + protocol is a significant benefit. + + 3. Reduction of Air-Link Resource Consumption + + Mobility-related signaling over the air-link is eliminated. + + 4. Support for Heterogeneous Wireless Link Technologies + + Since Proxy Mobile IPv4 is based on an access, technology- + independent, mobility protocol, it can be used for any type of + access network. + + From the network perspective, a mobile device is identified by + the Network Access Identifier (NAI) and the forwarding is set up + between the PMA and HA for the mobile device's current point of + attachment on the network. The mobile device may be attached to + + + +Leung, et al. Informational [Page 6] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + multiple networks concurrently, although the network treats each + access interface independently. This feature can be supported + with the use of the PMIPv4 Access Technology Type Extension + (Section 5.5). + + 5. Support for IPv4 and IPv6 Hosts + + As IPv6 increases in popularity, the host will likely be dual + stack. Adding IPv6 support to the host for Proxy Mobile IPv4 + involves the methods defined in [RFC5454]. There are additional + enhancements needed, which are described in "Proxy Mobile IPv6" + [RFC5213]. However, support for an IPv6 host is out of the scope + of this document. + +4. Overview of Proxy Mobile IPv4 + +4.1. Mobility Signaling for Mobile Device + + After the mobile device completes network-access authentication, the + PMA exchanges Proxy Mobile IPv4 registration messages with the HA to + set up proper routing and tunneling of packets from/to the Mobile + Node. The PMIPv4 client is responsible for initiating the Proxy + Mobile IPv4 registration. For integrated PMA, the PMIPv4 client and + the FA interaction is all within the node. In the case of split PMA + implementation, the interactions between the PMIPv4 client and the FA + are exposed. The interface between the PMIP Client and the FA in the + split PMA scenario is defined in a standards organization + specification [NWG] and is consequently out of the scope of this + document. + + The following call flows describe the operations of Proxy Mobile + IPv4. The initial network attachment, registration renewal, and + resource cleanup procedures are covered. Note that the protocols + that interact with Proxy Mobile IP are identified and explained in + more detail. The PPP/IPCP (IP Control Protocol) protocol involves a + PPP client in the mobile device and a Network Access Server (NAS) in + the AR. DHCP involves a DHCP client in the MN and a DHCP server in + either the AR or the HA. PMIPv4 involves a PMA in the AR and an HA + in the router on the home network. The Authentication, + Authorization, and Accounting (AAA) protocol involves a AAA client in + the AR and a AAA server in the network. The collocation of the + functional entities in the AR/HA enables parameters to be + shared/processed among the protocols. + + When the various network entities are not collocated, any sharing of + parameters or other state information between them is out of the + scope of this document. + + + + +Leung, et al. Informational [Page 7] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +4.1.1. Proxy Registration during Initial Network Attachment + + +----+ +-------+ +-------+ +-----+ + | | | AR / | | | | | + | MN | | PMA | | AAA | | HA | + | | | | | | | | + +----+ +-------+ +-------+ +-----+ + | | | | + | 1a | 1b | | + Authentication |<------------->|<----------->| | + | | | | + | 2 | | | + +-> |-------------->| | | + | | | 3 | | + | | |-------------------------->| <-+ + Address | | | | | |PMIP + Acquisition| | | 4 | | | + | | |<--------------------------| <-+ + | | 5 | | | + +-> |<--------------| | | + | | | | + | 6 | | | + Data Forwarding |<------------->|<=========================>| + | | | | + + Figure 1: Network Connection Setup + + The initial network-attachment procedure is described below. There + are three distinct phases. First, authentication and authorization + happen when the mobile device accesses the network. Then, the mobile + device attempts to obtain an IP address. This triggers Proxy Mobile + IP, which assigns/authorizes the IP address and sets up forwarding + between the PMA and HA. The host configuration parameters may be + passed in the PMIPv4 signaling. Finally, the mobile device + configures its IP stack with the IP address and the obtained host + configuration. Packets to and from the mobile device transit both + the PMA and HA. + + 1a. The mobile device establishes a L2 (Layer 2) link with the base + station (not shown) and performs access + authentication/authorization with the AR (Access Router). + During this phase, the mobile device may run either the + Challenge Handshake Authentication Protocol (CHAP) [RFC1994] if + PPP [RFC1661] is used or the Extensible Authentication Protocol + (EAP) [RFC3748] over foo (foo being the specific access + technology, or PANA [RFC4058]). The AR acts as the NAS (Network + Access Server) in this step. + + + + +Leung, et al. Informational [Page 8] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + 1b. The AAA client exchanges AAA messages with the AAA + infrastructure to perform authentication and authorization of + the mobile device. As part of this step, the AAA server may + download some information about the mobile device (e.g., the + user's profile, handset type, assigned Home Agent address, and + other capabilities of the mobile device). + + 2. The mobile device requests an IP address via a PPP/IPCP + [RFC1332] or DHCP [RFC2131]. Specifically for PPP, the PPP + client sends an IPCP Configure-Request to the NAS. As for DHCP, + the DHCP client sends the DHCP Discover message to the DHCP + relay agent/ server. + + For the DHCP case, the DHCP server or DHCP relay agent sends the + DHCP Ack message to the DHCP client after PMIPv4 signaling has + completed. + + 3. Triggered by step 2, the PMA sends a Proxy Registration Request + (PRRQ) to the HA. The HA's IP address is either obtained from + the AAA server at step 1b or discovered by some other method. + The PRRQ contains the Care-of Address (CoA) of the PMA (the + collocated FA in this case). The Home Address field is set to + zero or the IP address is specified as a hint in the DHCP or + IPCP message. The PRRQ MUST be protected by the methods + described in the Security Considerations (Section 13) of this + document. The derivation and distribution of the MN-HA or FA-HA + key is outside the scope of this document. + + 4. The Home Agent sets up the mobility binding entry for the mobile + device after assigning an IP address or authorizing the + requested Home Address. The Home Agent may also assign a + Generic Routing Encapsulation (GRE) key in this step (if GRE + tunneling is used between the PMA and HA). The HA returns the + Home Address and the GRE key (if applicable) in the Proxy + Registration Reply (PRRP) to the PMA. If the requested Home + Address is not authorized, the Home Agent denies the + registration with error code 129 (administratively prohibited). + After the PMA processes the PRRP, the forwarding path for the + Home Address between the PMA and HA is established. A GRE + tunnel may be used between the PMA and the HA [MIP4GREKEY]. + This event completes the Proxy Mobile IPv4 signaling for initial + network attachment. + + 5. After the Proxy Mobile IPv4 registration exchange, the AR + provides the IP address to the mobile device in response to step + 2. For IPCP, the NAS replies to the PPP client with an IPCP + Configure-Nak, which includes the PMIPv4-assigned Home Address + + + + +Leung, et al. Informational [Page 9] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + in the IP address configuration option and the DNS server + address in the IPCP configuration option. + + The following procedure happens when the DHCP server is on the + AR. The DHCP server sends a DHCP Offer with the PMIPv4-assigned + Home Address in the yiaddr field to the DHCP client. The DHCP + client sends a DHCP Request to the DHCP server, which replies + with a DHCP Ack. The host configuration (such as the DNS server + address) is included in the DHCP options in the message. Note + that the DHCP messages are exchanged directly between the DHCP + client and the DHCP server. + + In the case when AR acts as a DHCP relay agent, the DHCP + Discover is relayed to the DHCP server on the HA. The DHCP + server sends a DHCP Offer with the PMIPv4-assigned Home Address + in the yiaddr field to the DHCP relay agent, which forwards it + to the DHCP client. The DHCP Request and DHCP Ack messages are + exchanged between the DHCP client and DHCP server via the DHCP + relay agent. Regardless of the sequence of PMIPv4 signaling and + DHCP exchanges, the interaction between PMIPv4 and DHCP involves + in the same IP address for Home Address field and yiaddr field, + respectively. + + 6. At this step, the mobile device's IP stack is configured with an + IP address that has a forwarding path between the AR/PMA and HA. + Also, the host configuration (such as DNS servers) is configured + at this time. Now that the IPCP or DHCP procedure has + completed, the mobile device is ready to receive or send IP + packets. If DHCP is used, the DHCP client renews the IP address + by sending a DHCP Request directly to the DHCP server. The + lease for the IP address is extended when a DHCP Ack from the + DHCP server is received by the DHCP client. + + + + + + + + + + + + + + + + + + + +Leung, et al. Informational [Page 10] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +4.1.2. Proxy Registration Renewal + + +----+ +-------+ +-----+ + | | | AR / | | | + | MN | | PMA | | HA | + | | | | | | + +----+ +-------+ +-----+ + | | | + | | 1 | + | |----------------------->| + PMIPv4 | | | + Renewal | | 2 | + | |<-----------------------| + | | | + | | | + + Figure 2: Network Connection Maintenance + + The network-connection maintenance procedure is described below. As + long as the mobile device remains attached to the AR, the Proxy + Mobile IPv4 session is maintained by re-registration exchanges + between the AR and HA. + + 1. Before the PMIPv4 registration lifetime expires, and assuming the + AR has not received any indication that the mobile device + detached from the network, the PMA sends a PRRQ to the HA to + extend the duration of the mobility binding of the mobile device. + This PRRQ is similar to the initial PRRQ (i.e., HA field set to + the assigned HA, and CoA field set to the PMA), though the Home + Address field is always set to the assigned IP address of the + mobile device. The mobile device's IP stack can continue to send + and receive IP packets using the Home Address anchored at the HA. + + 2. The HA sends the PRRP in response to the PRRQ received from the + PMA. After the PMA processes the PRRP, the forwarding path + between AR and HA remains intact. + + + + + + + + + + + + + + + +Leung, et al. Informational [Page 11] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +4.1.3. Proxy Handover Support + + +----+ +-------+ +-------+ +-----+ + | | | New | | Old | | | + | MN | | AR / | | AR / | | HA | + | | | PMA | | PMA | | | + +----+ +-------+ +-------+ +-----+ + | | | | + | 1 | | | + Authentication |<------------->| | | + | | | | + | | 2 | | + +-> | |-------------------------->| + PMIPv4 | | | | | + | | | 3 | | + +-> | |<--------------------------| + | | | | + | 4 | | | + Data Forwarding |<------------->|<=========================>| + | | | | + + Figure 3: AR Handover + + The AR handover procedure is described below. There are three + phases. First, authentication and authorization happen when the + mobile device attaches to the new AR in the network. The successful + authentication triggers the Proxy Mobile IPv4 signaling. In the last + phase, the forwarding path between the new AR and HA is set up for + the mobile device to send and receive IP packets using the same Home + Address anchored at the HA. + + 1. The mobile device establishes L2 link with the base station (not + shown) and performs access authentication/authorization with the + new AR, using the security method for network re-attachment. + + 2. Triggered by successful authentication, the PMA sends a PRRQ to + the HA. The HA's IP address is typically obtained or is known by + the method used for fast re-authentication during AR handover + (e.g., context transfer between the two ARs), though other + methods may be used. The PRRQ contains the CoA of the new PMA. + The Home Address field is set to zero or the assigned IP address + of the mobile device. The IP address is also obtained/known by + the same method mentioned before. + + 3. The Home Agent updates the existing mobility binding entry for + the mobile device upon processing the PRRQ. The Home Agent + returns the Home Address, fetched from the binding, in the PRRP + to the new PMA. After the PMA processes the PRRP, the forwarding + + + +Leung, et al. Informational [Page 12] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + path for the Home Address between the new AR and HA is + established. The event completes the Proxy Mobile IPv4 signaling + for AR handover. + + 4. At this step, which happens around the same time as step 2, the + mobile device's IP stack may detect L2 link going down and up + after access re-authentication. The mobile device's IP stack may + attempt to validate its IP address connectivity. See Sections + 6.1, 6.2, and 6.3 of this document for considerations on ARP + [RFCARP], ICMP [RFCICMP], and DHCP [RFC2131], respectively. + Because the forwarding path is established between the new PMA + and HA, the mobile device can receive or send IP packets using + the Home Address. + +4.1.4. Resource Cleanup + + +----+ +-------+ +-------+ +-----+ + | | | New | | Old | | | + | MN | | AR / | | AR / | | HA | + | | | PMA | | PMA | | | + +----+ +-------+ +-------+ +-----+ + | | | | + | | | 1 | + +-> | | |<------------| + | | | | | + Revocation | | | o 2 | + | | | | | + | | | | 3 | + +-> | | |------------>| + | | | | + + Figure 4: Registration Revocation for Previous PMA + + The resource cleanup procedure for the old AR is described below. + This cleanup is necessary when the old AR needs to delete its PMIPv4 + and other associated states for a mobile device that has moved to + another AR. Therefore, this is an optional procedure for Proxy + Mobile IP. The alternative method is based on the new PMA notifying + the old PMA to clean up resources. The alternative method is out of + the scope of this document. + + 1. Triggered by the update of the mobility binding entry for a + mobile device that has moved to a new AR, the HA may send a + Registration Revocation (as specified in RFC 3543 [RFC3543]) to + the old PMA (i.e., specifically to the Foreign Agent entity) in + order to clean up unused resources in an expeditious manner. + + + + + +Leung, et al. Informational [Page 13] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + 2. The old PMA removes the PMIPv4 states for the mobile device. + + 3. The old PMA sends revocation acknowledgement to the HA. + +4.2. Establishment of a Bi-Directional Tunnel + + The PMA and HA set up a tunnel between them for the Home Address + after the PMIPv4 registration message exchange. + +4.2.1. Packet Forwarding + + The bi-directional tunnel between the PMA and the HA allows packets + to flow in both directions, while the mobile device is connected on + the visited network. All traffic to and from the mobile device + travels through this tunnel. + + While the PMA is serving a mobile device, it MUST be able to + intercept all packets sent from the mobile device and forward them + out the tunnel created for supporting that mobile device. Typically, + forwarding is based on layer 2 information such as the source Media + Access Control (MAC) address or ingress interface. This allows + overlapping IP addresses to be supported for the packet from the + mobile device. For example, the PMA forwards packets from mobile + devices with the same IP address to the tunnel associated with each + mobile device, based on the source MAC address. + + The PMA de-encapsulates any packets received on the tunnel from the + HA before forwarding to the mobile device on its link. Typically, + the forwarding is based on the destination IP address and ingress HA + tunnel (which may have a GRE key). This allows overlapping IP + addresses to be supported for the packet destined to the mobile + device. For example, the PMA forwards packets to mobile devices with + the same IP address to the link associated with each mobile device, + based on the GRE key value of the tunnel created for the HA that + serves these mobile devices. + + The tunnel operation between the PMA and HA is the same as between + the FA and HA in RFC 3344. The IP TTL (Time to Live), fragmentation, + re-assembly, etc. logic remain the same. The tunnel mode is IPinIP + by default or GRE as an option. + +4.2.2. Broadcast and Multicast + + Broadcast packet processing for DHCP and ARP (Address Resolution + Protocol) messages are described in Section 6.3 and Section 6.1, + respectively. For other types of broadcast packets, the PMA and HA + + + + + +Leung, et al. Informational [Page 14] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + process them in accordance to [RFC3344], [RFC3024], and [MIP4MCBC]. + Only the Direct Encapsulation Delivery Style is supported, as there + is no encapsulation for the packets between the mobile device and + PMA. + +4.2.3. Forwarding between Devices on the Same PMA + + When the communication peers are both attached to the same PMA, the + packet is forwarded as specified in Section 4.2.1. The traffic + between them should be routed via the HA without taking a local + shortcut on the PMA. This ensures that data-traffic enforcement at + the HA is not bypassed. + +4.3. Security Association between the PMA and the HA + + The security relationship for protecting the control message + exchanges between the PMA and the HA may be either per node (i.e., + same security association for all mobile devices) or per MN (i.e., + unique security association per mobile device). The method of + obtaining the security association is outside the scope of this + document. + + For per-node SA support, the FA-HA Authentication extension or IPsec + (indicated in the PMIPv4 extension) is used to authenticate the + signaling messages (including Registration Revocation [RFC3543]) + between PMA and HA. In the case of IPsec, Encapsulating Security + Payload (ESP) [RFC4303] in transport mode with mandatory integrity + protection should be used. The IPsec endpoints are the IP addresses + of the PMA and HA. + + For per-MN SA support, the MN-HA Authentication extension and/or MN- + AAA Authentication extension are used to authenticate the signaling. + + The creation of the security association may be assisted by the AAA + server at the time of access authentication. + +4.4. Registration Sequencing + + The Identification field in the registration message provides replay + protection and sequencing when the timestamp method is used. This + mechanism allows the HA to know the sequence of messages from the + same PMA or different PMAs based on the Identification field. The HA + can also synchronize the PMA's clock by using the Identification + mismatch error code in the Proxy Registration Reply. This reply + message would not be necessary when the PMA's clocks are synchronized + using the Network Time Protocol [RFC1305] or some other method. Note + that the use of nonce for sequencing and replay protection is outside + the scope of this document. + + + +Leung, et al. Informational [Page 15] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + The method above is sufficient when there is a single source for + signaling as in the split PMA case. However, in the integrated PMA + case, the Proxy Registration Request is sent from different sources + (i.e., different PMAs). If the previous PMA is unaware that the + mobile device has moved away and continues to send re-registration, + then the HA would be misinformed on the location of the device. + Therefore, an integrated PMA MUST confirm that the mobile device is + still attached before sending a Proxy Registration Request. + + Note that, for the split PMA model as used in WiMAX Forum (see + Section 10), the PMIPv4 client remains anchored during handover (see + Section 10.1). In this case, the PMIPv4 client is the only source of + the PRRQ. However, there are cases (such as PMIPv4 client relocation + and uncontrolled handover events) when more than one PMA performs + registration. The same method for the integrated PMA is used to + ensure proper sequencing of registration on the HA. + +4.5. Mobile Device Interface Configuration + + Typically, the mobile device's interface needs to be configured with + an IP address, network prefix, default gateway, and DNS server + addresses before the network connection can be enabled to be used for + communication. For some IP stacks, the default gateway IP address + has to be on the same subnet as the mobile device's IP address. When + the Home Agent's IP address is not on the same subnet as the Home + Address, vendor-specific extensions (e.g., [RFC4332]) or other + methods MAY be used by the PMA to obtain the default gateway. + +4.6. Dynamic HA Discovery + + The PMA can perform dynamic HA discovery by sending the registration + with Home Agent field set to 0.0.0.0 or 255.255.255.255. The Home + Agent responds with its IP address in the Home Agent field as + specified in "Mobile IPv4 Dynamic Home Agent (HA) Assignment" + [RFC4433]. + +5. Proxy Mobile IPv4 Extensions + + The following PMIPv4 extensions are not required for base + functionality but may be used in some cases where such features are + applicable. They are included before the authentication extension + (e.g., MN-HA or FA-HA Authentication extension) in the registration + message. + + + + + + + + +Leung, et al. Informational [Page 16] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +5.1. PMIPv4 Per-Node Authentication Method Extension + + The Proxy Mobile IPv4 Authentication Method extension indicates + alternative methods for authenticating the registration besides the + default MN-HA Authentication extension as specified in RFC 3344. + This extension MUST be included in the Registration Request and + Registration Reply when the security association for authenticating + the message is between the PMA and HA on a per-node basis. This + means that a common key or set of keys (indexed by the SPI) are used + for message authentication by the PMA and HA. The key is independent + of the mobile device, which is identified in the registration. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Type | Sub-Type | Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Method | + +-+-+-+-+-+-+-+-+ + + PMIPv4 Per-Node Authentication Method Extension + + Type + + 47 (Proxy Mobile IPv4 Non-Skippable Extension) + + Sub-Type + + 1 (PMIPv4 Per-Node Authentication Method) + + Length + + 1 + + Method + + An 8-bit field that specifies the authentication type for + protecting the signaling messages. + + The values (0 - 255) are allocated and managed by IANA. The + following values have been assigned to the specified method + types. + + 0: Reserved + + 1: FA-HA Authentication + + 2: IPsec Authentication + + + +Leung, et al. Informational [Page 17] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +5.2. Proxy Mobile IPv4 Interface ID Extension + + The Proxy Mobile IPv4 Interface ID extension identifies the interface + address of the device used to attach to the network. The information + MAY be included in the Registration Request when the PMA is aware of + it. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Type | Length | Sub-Type | Identifier ... + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + PMIPv4 Interface ID Extension + + Type + + 147 (Proxy Mobile IPv4 Skippable Extension) + + Length + + The length of the extension in octets, excluding Type and + Length fields. + + Sub-Type + + 1 (PMIPv4 Interface ID) + + Identifier + + A variable-length octet sequence that contains an identifier of + the interface. + +5.3. Proxy Mobile IPv4 Device ID Extension + + The Proxy Mobile IPv4 Device ID extension identifies the device used + to connect to the network. The information MAY be included in the + Registration Request when the PMA is aware of it. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Type | Length | Sub-Type | ID-Type | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Identifier ... + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + PMIPv4 Device ID Extension + + + +Leung, et al. Informational [Page 18] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + Type + + 147 (Proxy Mobile IPv4 Skippable Extension) + + Length + + The length of the extension in octets, excluding Type and + Length fields. + + Sub-Type + + 2 (PMIPv4 Device ID) + + ID-Type + + An 8-bit field that specifies the device ID type. + + The values (0 - 255) are allocated and managed by IANA. The + following values have been assigned to the specified device ID + types. + + 0: Reserved + + 1: Ethernet MAC address + + 2: Mobile Equipment Identifier (MEID) + + 3: International Mobile Equipment Identity (IMEI) + + 4: Electronic Serial Number (ESN) + + Identifier + + A variable-length octet sequence that contains an identifier of + the type indicated by the ID-Type field. + +5.4. Proxy Mobile IPv4 Subscriber ID Extension + + The Proxy Mobile IPv4 Subscriber ID extension identifies the mobile + subscription. The information MAY be included in the Registration + Request when the PMA is aware of it. + + + + + + + + + + +Leung, et al. Informational [Page 19] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Type | Length | Sub-Type | ID-Type | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Identifier ... + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + PMIPv4 Subscriber ID Extension + + Type + + 147 (Proxy Mobile IPv4 Skippable Extension) + + Length + + The length of the extension in octets, excluding Type and + Length fields. + + Sub-Type + + 3 (PMIPv4 Subscriber ID) + + ID-Type + + An 8-bit field that specifies the subscriber ID type. + + The values (0 - 255) are allocated and managed by IANA. The + following values have been assigned to the specified subscriber + ID types. + + 0: Reserved + + 1: International Mobile Subscriber Identity (IMSI) + + Identifier + + A variable-length octet sequence that contains an identifier of + the type indicated by the ID-Type field. + +5.5. PMIPv4 Access Technology Type Extension + + The Proxy Mobile IPv4 Access Technology Type extension indicates the + type of radio-access technology on which the mobile device is + attached. This extension MAY be included in the Registration Request + when the PMA is aware of the information. The HA can provide + mobility on the same access technology type for a mobile device with + + + + +Leung, et al. Informational [Page 20] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + multiple interfaces, assuming each interface is connected on a + different access technology type. The HA does not include the + extension in the associated Registration Reply. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Type | Length | Sub-Type | Tech-Type | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + PMIPv4 Access Technology Type Extension + + Type + + 147 (Proxy Mobile IPv4 Skippable Extension) + + Length + + 2 + + Sub-Type + + 4 (Access Technology Type) + + Tech-Type + + An 8-bit field that specifies the access technology through + which the mobile device is connected to the access network. + + The values (0 - 255) are allocated and managed by IANA. The + following values have been assigned to the specified access + technology types. + + 0: Reserved + + 1: 802.3 + + 2: 802.11a/b/g + + 3: 802.16e + + 4: 802.16m + + 5: 3GPP EUTRAN/LTE + + 6: 3GPP UTRAN/GERAN + + + + + +Leung, et al. Informational [Page 21] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + 7: 3GPP2 1xRTT/HRPD + + 8: 3GPP2 UMB + +6. Appearance of Being at Home Network + + Since the Mobile Node is not aware of its mobility and does not + participate in handover signaling, the network entities emulate the + home network to the mobile device attached on the network. From the + mobile device's perspective, it operates as if it were at the home + network. However, the network is directing the mobile device's + traffic to and from its current location and will continue to do so + when it moves to a new location. + + An unmodified mobile device on a shared link learns the MAC address + of another host on the home network via ARP ([RFCARP]), obtains an IP + address and other host configuration via DHCP ([RFC2131]), and sends + link-local multicast and broadcast packets. The network's response + to the host is equivalent to the situation when a host is on the home + network. When the link state changes, some hosts use ARP, ICMP, + and/or DHCP to detect if it has changed the point of attachment on + the network. + +6.1. ARP Considerations + + For IEEE 802 type of access networks (e.g., WLAN, WiMAX Ethernet + Convergence Sublayer), the mobile device sends ARP requests for the + Corresponding Node (CN) and default gateway on the same network. The + purpose of maintaining an ARP entry is to allow the delivery of the + packet from the mobile device to the CN using the destination MAC + address. The ARP procedure for resolving IP and MAC address mapping + is not needed for 3GPP2's cdma2000 and WiMAX IP Convergence Sublayer + networks. + + The access router is always the L2 endpoint for the mobile device. + The destination MAC address in the packet does not need to be set to + the CN's MAC address. As long as the packet can be received by the + access router, it will be forwarded toward the CN via the home + network node (further details in Section 4.2.1). The ARP table in + the mobile device does not need to be populated with CNs' MAC + addresses in order for the packet to reach the CNs. + + A mobile device has ARP entries for the default gateway and hosts on + the same subnet. Regardless of what the MAC addresses are, the AR + receives the packets sent from the mobile device. + + + + + + +Leung, et al. Informational [Page 22] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +6.2. ICMP Considerations + + For movement detection, certain types of network stack on the mobile + device will send an ICMP request [RFCICMP] to the default gateway + after detecting the link went down and up. The IP TTL in the message + is set to 1 to check if the default gateway is still directly + reachable on the access network. The PMA MAY send an ICMP reply when + it is providing Proxy Mobile IPv4 service for the mobile device. + This response confirms to the mobile device that it has remained on + the home network after link state change. This behavior is observed + on existing client implementation. "Detecting Network Attachment in + IPv4 (DNAv4)" [RFC4436] can be employed. + + General ICMP traffic is handled as normal IP packets and tunneled + between the PMA and HA. + +6.3. DHCP Considerations + + DHCP [RFC2131] is used to obtain an IP address and other host + configuration parameters for a mobile device. The mobile device is + expected to behave as a normal DHCP client when connected to the + network with Proxy Mobile IPv4 service. There are two DHCP phases: + bootup and renewal/release. The bootup procedure relies on the DHCP + relay agent to obtain a lease on the IP address for the DHCP client + from the DHCP server. The DHCP client directly renews and releases + the lease with the DHCP server. + + In Proxy Mobile IPv4, the mobile device boots up on a network that is + not the home network associated with the leased IP address. Also, + the mobile device can move to other networks that are not related to + that IP address. Yet, the DHCP client on the mobile device continues + to operate as a stationary device that is directly on the network + associated with its IP address. The PMA and HA create the + transparency of the remote home network and mobility events by + providing the expected network response to the DHCP client. + + There are several methods for the network infrastructure to interface + with the mobile device such that the mobile device believes it is + always fixed on the same network. The following methods are + identified here, though others may be used as well. + + DHCP Server in the AR: + + The mobile device boots up and initiates DHCP. The procedure is + described in Figure 1. The DHCP client renews or releases the IP + address directly with the DHCP server in the AR. When the mobile + device is on a different AR than the AR/DHCP server, the DHCP + message from the client needs to be able to either be forwarded to + + + +Leung, et al. Informational [Page 23] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + the DHCP server in the previous AR or handled by the DHCP server + in the new AR. When the DHCP lease time expires for the mobile + device's IP address or the DHCP release message is received on the + current AR, the AR sends PMIPv4 de-registration to the HA. + + DHCP Relay Agent in the AR: + + The mobile device boots up and initiates DHCP. The procedure is + described in Figure 1. The DHCP client renews or releases the IP + address directly with the DHCP server in the HA. When the mobile + device is on a different AR, DHCP messages from the client are + relayed to the DHCP server in the HA. When the DHCP lease time + expires for the mobile device's IP address or the DHCP release + message is received on the HA, the HA deletes the mobility binding + entry for the mobile device and sends registration revocation + [RFC3543] to the AR. + +6.4. PPP IPCP Considerations + + When the mobile device accesses the network via PPP [RFC1661], LCP + (Link Control Protocol) CHAP is used to authenticate the user. After + authentication, the NAS (which is the AR/PMA) sends the Proxy Mobile + IPv4 Registration Request to the HA. The HA responds with the Home + Address in the Proxy Registration Reply. The NAS informs the mobile + device to use the Home Address during IPCP [RFC1332]. When the + mobile device moves to a new NAS, the same procedure happens and that + mobile device has the same IP address for communication. + + The message exchange is illustrated in Figure 1. + +6.5. Link-Local Multicast and Broadcast Considerations + + Depending on configuration policies, the PMA may tunnel all packets + destined to Link-Local Multicast or Broadcast to the HA. The HA + looks up the hosts that are in the same subnet and sends a duplicated + packet to each of them. + +7. Proxy Mobility Agent Operation + + The PMA performs the functions of a Mobile Node entity as described + in RFC 3344, with the exceptions identified below. + + - No agent discovery (i.e., agent solicitation and advertisement) is + supported. + + - The D-bit (De-encapsulation by MN) in the Registration Request is + always set to zero. + + + + +Leung, et al. Informational [Page 24] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + The main responsibility of the PMA is to set up and maintain the + routing path between itself and the HA for a mobile device that is + attached on the network. When it detects a mobile device is no + longer attached, the routing path is torn down. It is possible that + the PMA functions may be split up in implementations such as WiMAX + (Section 10). + + The PMA needs to know the following information, at a minimum, for + sending a proxy registration: + + 1. NAI of the mobile device. + + 2. MN-HA security association, when per-mobile device security + association is used. + + 3. FA-HA Mobility security association or IPsec security association + when per-node security association is used. Note that these + associations are specific only between PMA and HA, and are + cryptographically unrelated to the associations between the MN + and other network nodes. + + 4. HA Address. + + This information is typically downloaded from the AAA server during + access authentication. + +8. Home Agent Operation + + The Home Agent has the functionality described in RFC 3344 [RFC3344]. + In addition, the following features are introduced by Proxy Mobile + IPv4: + + 1. Sequencing between PRRQs from multiple PMAs. For the integrated + PMA case, there is a period after handover that may result in + both the new PMA and old PMA sending PRRQs. It is imperative + that the old PMA confirm that the mobile device is attached + before sending a PRRQ when the re-registration timer expires. + This would ensure that the HA only receives registration from the + PMA that is serving the mobile device. + + 2. Authentication of PRRQs based on per-node security associations + (FA-HA AE or IPsec AH/ESP) is applicable in the integrated PMA + case. The presence of MN-HA AE or MN-AAA AE in the PRRQ is not + necessary in this case. Since PMIPv4 is based on signaling + between the PMA and the HA, the security for the message can be + authenticated based on the peers' relationship. The HA can + authorize PMIPv4 service for the mobile device at the PMA by + contacting the AAA server. + + + +Leung, et al. Informational [Page 25] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + 3. The ability to process the Proxy Mobile IPv4 extensions defined + in this document for enhanced capabilities of PMIPv4. + +8.1. Processing Proxy Registration Requests + + When a Proxy Registration Request is received, the HA looks up the + mobility binding entry indexed by the NAI. If the entry exists, HA + compares the sequence numbers between the message and mobility + binding entry (MBE), if present. If the value in the message is zero + or greater than or equal to the one in the MBE, HA accepts the + registration. The HA replies with a sequence number that is one + greater than the larger value of either the MBE or Proxy Registration + Request. If the registration is denied, then HA sends error code + "Administratively prohibited (65)". If the HA is not enabled with + Proxy Mobile IPv4 or cannot process the Proxy Mobile IPv4 Extensions + defined in this document, it sends a Registration Reply with error + code PMIP_UNSUPPORTED ("Proxy Registration not supported by the HA"). + In the case when the PMA is not allowed to send a Proxy Registration + Request to the HA, the HA sends a Proxy Registration Reply with error + code PMIP_DISALLOWED ("Proxy Registrations from this PMA are not + allowed"). + + A PMA receiving these error codes SHOULD NOT retry sending Proxy + Mobile IPv4 messages to the HA that sent replies with these error + codes. + +9. Mobile Device Operation + + As per this specification, a mobile device would function as a normal + IPv4 host. The required behavior of the node will be consistent with + the base IPv4 specification [RFC0791]. The mobile station will have + the ability to retain its IPv4 address as it moves from one point of + network attachment to the other without ever requiring it to + participate in any mobility-related signaling. + + When booting up for the first time, a mobile device obtains an IPv4 + address using DHCP or IPCP. + + As the mobile device roams, it is always able to communicate using + the obtained IP address on the home network. The PMA on the + currently attached network signals to the HA to ensure a proper + forwarding path for the mobile device's traffic. + + + + + + + + + +Leung, et al. Informational [Page 26] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +9.1. Initial Network Access + + When the mobile device accesses the network for the first time and + attaches to a network on the PMA, it will present its identity in the + form of an NAI to the network as part of the network-access + authentication process. + + Once the address configuration is complete, the mobile device will + always be able to use that IP address anywhere in the network. + +9.2. Mobile Device Mobility + + When a mobile device moves to a new PMA from another PMA, the + following occurs: + + The mobile device may perform a network-access authentication with + the new AR/PMA. If the authentication fails, the mobile device will + not be able to use the link. After a successful authentication, the + new PMA will have the identifier and the other profile data of the + mobile device. The new PMA can also obtain the mobile device's + information using a context-transfer mechanism, which is out of the + scope of this document. + + Once the network-access authentication process is complete, the + mobile device may sense a change in the Link Layer and use ARP, DHCP, + and/or ICMP to detect if it is still on the same subnet. These + mechanisms are handled by the network as described in "Appearance of + Being At Home Network" (Section 6). + +9.3. Sending and Receiving Packets + + All packets that are to be sent from the mobile device to the + Corresponding Node (CN) will be sent as normal IPv4 packets, setting + the Source Address of the IPv4 header to the Home Address and the + Destination Address to the Corresponding Node's IP address. In Proxy + Mobile IPv4 operation, the default gateway for the mobile device is + set up to reach the PMA. + + Similarly, all packets sent to the mobile device's IP address by the + Corresponding Node will be received by the mobile device in the + original form (without any tunneling overhead). + + For Proxy Mobile IP, the packet from the mobile device is transported + to the HA to reach the destination, regardless of the destination IP + address. For a CN with an IP address on the same network as the + mobile device but that is physically located elsewhere, the HA will + tunnel the packet to the CN. Otherwise, the HA forwards the traffic + via normal routing. + + + +Leung, et al. Informational [Page 27] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + No special operation is required by the mobile device to either send + or receive packets. + + Mobile devices attached to the same PMA may be using different HAs + for transporting their traffic. + +10. Proxy Mobile IPv4 Use Case in WiMAX + + WiMAX Forum Network Working Group (NWG) uses the Proxy Mobile IPv4 + scheme to provide IPv4 connectivity and IP mobility. The relevant + specification from WiMAX Forum is [NWG]. + + The Proxy Mobile IPv4 protocol is used over NWG reference point 3 + (R3). Most of the Proxy Mobile IPv4 related procedures and + requirements are described in reference to mobility management over + R3. + + The Proxy Mobile IPv4 use case in the WiMAX Forum specification is + illustrated in the following diagram: + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Leung, et al. Informational [Page 28] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + | + | CSN + | + | + +-------+ | +-------+ + | | | | | + |AAAV |--------------|------------| AAAH | + | | | | | + | | | | | + +-------+ | +-------+ + | | | + | | | + | | | + +------------------+ | | + | +-------+ | | | + | | NAS | | | | + | | PMIP | ASN1 | | | + | | Client| | | | + | +-------+ | | | + | | | | | + | | R4 | | | + | +-------+ | | +------+ + +----+ | | FA, | | | PMIPv4 | | + | MN |-------| DHCP |---------------------------| HA | + +----+ | | Relay/| | | R3 | | + | | Server| ASN2 | | +------+ + | +-------+ | | + | | | + +------------------+ + Split PMA + + Figure 5: WiMAX NWG Network Configuration for PMIPv4 Use + + As shown in the figure above, WiMAX NWG uses the split PMA model. + The PMIPv4 client is collocated with the NAS in ASN1 (aka, + Authenticator ASN). The NWG architecture divides the network into + two parts. The Access part is termed the "Access Service Network" + (ASN). The Core part is termed the "Connectivity Service Network" + (CSN). The MN attaches to an 802.16 radio in the ASN2 (aka, Anchor + Data Path Function). The radio (base station) connects to the Anchor + Data Path Function (A_DPF) in ASN2, which in turn connects to the + Authenticator ASN (NAS) in ASN1. ASN1 authenticates and authorizes + the MN. The AAA infrastructure is used to authenticate and authorize + the MN. + + Note that, during initial network entry by the MN, the PMA can be an + integrated PMA with all the functions collocated in ASN1. Due to + mobility, the FA part of the PMA may have to be relocated to a more + + + +Leung, et al. Informational [Page 29] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + optimized location for better bearer management. However, to + describe the WiMAX specific use case for Proxy Mobile IPv4, we will + use the split PMA model since it is a more generic representation of + the WiMAX NWG mobility framework. + + The WiMAX NWG specification [NWG] defines a key bootstrapping scheme + for use with Proxy Mobile IPv4. The specification uses per-MN + security association for Proxy Mobile IPv4 operation. The relevant + keys (e.g., MN-HA key) are derived using EAP authentication as + specified in this document. For more information, please refer to + Section 4.3 of [NWG], stage-3 specification. + + Mobile IPv4 Registration Revocation is optionally supported in WiMAX. + The security association for this is per node. It is provided with + FA-HA AE. The FA-HA key is also bootstrapped via the same key + hierarchy that is described in Section 4.3 of [NWG]. + + The Proxy Mobile IPv4 operation in WiMAX NWG is aligned with the + basic Proxy Mobile IPv4 operation as described in Section 4 of this + document. There are specific considerations for WiMAX NWG 1.0.0 use + of Proxy Mobile IPv4. These are listed below: + + 1. Use of per-MS SA for Proxy Mobile IPv4 registration. In this + case, MN-HA AE is used. + + 2. Use of split PMA to handle FA relocation while the PMIPv4 client + remains anchored with the NAS (Authenticator ASN). + + 3. Only the Proxy Mobile IPv4 Access Technology Type extension + defined in this document is used in the NWG specification [NWG]. + + 4. GRE key identifier is optionally used between the HA and the PMA. + + 5. The PMIPv4 client and the FA interact via the WiMAX specific + reference point and protocol (aka, R4). For more information, + please refer to the NWG specification [NWG]. + + 6. In order to handle inter-ASN (inter Access Router) handover and + still allow the MN to use the same DHCP server's IP address that + was sent in DHCPOFFER/ACK, the DHCP server (aka, proxy) functions + in the ASN are required to be configured with the same IP + address. + + 7. The MN - AR (trigger for Proxy Mobile IPv4) interaction is based + on DHCP. DHCPDISCOVER from the MN triggers the Proxy Mobile IPv4 + process in the ASN. + + + + + +Leung, et al. Informational [Page 30] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +10.1. Proxy Mobile IPv4 Call Flow Examples with Split PMA in WiMAX + + Since WiMAX uses the split PMA model, the call flows involve WiMAX + proprietary signaling between the PMIPv4 client and FA within the + PMA. The following call flows illustrate this. + + Split PMA + +-----------------------------------+ + +----+ | +------+ +------+ +-----+ | +-----+ + | | | | NAS/ | | Old | | New | | | | + | MN | | | PMIP | | FA | | FA | | | HA | + | | | |Client| | | | | | | | + +----+ | +------+ +------+ +-----+ | +-----+ + | +----|------------|------------|----+ | + | | | PMIP Tunnel | + | | |<=======================>| + | | | | | + | | | R4 tunnel | | + | | |<==========>| | + | | 1 | | | + |<---------------------------------->| | + | | | | | + | | | 2 | | + | | |<---------->| | + | | 3 | | | + | |<----------------------- | | + | | | | | + | | 4 | | | + +-> | |------------------------>| | + | | | | | 5 | + | | | | |----------->| + | | | | | | + PMIP | | | | | 6 | + | | | | |<-----------| + | | | | | | + | | | 7 | | | + +-> | |<------------------------| | + | | | | | + | | | 8 | | + | | |<---------->| | + | | | | | + | 9 | | |PMIP Tunnel | + Data |<---------------------------------->|<==========>| + Forwarding | | | | | + + Figure 6: Proxy Handover Operation in WiMAX with Split PMA + + + + + +Leung, et al. Informational [Page 31] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + In this scenario, the MN has moved to a new FA's area (known as the + Data Path Function in WiMAX). The old FA and the new FA interact + with each other and also with the PMIPv4 client over a WiMAX- + specified R4 reference point to perform the handover. The steps are + described below: + + 1. The mobile device establishes a L2 link with a base station (not + shown), which connects to a new FA (aka, new Data Path Function + in WiMAX). Note that, in this case, the MN does not perform + authentication and authorization. The PMIPv4 tunnel remains + between the old FA (aka, old Data Path Function in WiMAX). The + data flows through the PMIPv4 tunnel between the HA and the old + FA, and through the WiMAX-specific R4 tunnel between the old FA + and the new FA and from the new FA to the MN. + + 2. The new FA interacts with the old FA using a WiMAX-specific R4 + reference point to initiate the handover process. + + 3. The new FA uses the WiMAX-specific R4 reference point to request + the PMIPv4 client to begin the PMIPv4 handover. + + 4. Triggered by step 3, the PMIPv4 client sends a PRRQ to the new + FA. The PRRQ contains the FA-CoA of the new FA. The Home + Address field is set to the address of the assigned IP address of + the Mobile Node. The PRRQ is embedded in the WiMAX-specific R4 + packet. + + 5. The new FA forwards the PRRQ to the HA. + + 6. The Home Agent updates the existing mobility binding entry for + the mobile device upon processing the PRRQ. The Home Agent + responds back to the new FA with PRRP. + + 7. The new FA forwards the PRRP after encapsulating it in a WiMAX- + specific R4 packet to the PMIPv4 client. + + 8. The new FA and the old FA exchange WiMAX-specific R4 messages + between them to confirm the handover. The old FA cleans up its + resources for the MN. The R4 bearer forwarding also stops at + this point. + + 9. The forward and reverse direction traffic flows via the new FA. + The handover is complete at this point. + + + + + + + + +Leung, et al. Informational [Page 32] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +11. Proxy Mobile IPv4 Use Case in 3GPP2 + + 3GPP2 uses the Proxy Mobile IPv4 scheme to provide mobility service + for the following scenarios (as shown in the figures below): + + 1. Mobility between the base station (BS) and access gateway (AGW) + + 2. Mobility between the AGW and the Home Agent (HA). + + As shown in the diagrams below, in use case 1, the BS acts as the PMA + and the AGW acts as the HA for Proxy Mobile IPv4 operation. In use + case 2, the AGW acts as the PMA while the HA assumes the role of the + Home Agent. + + RAN Core + + +-------+ +------+ + +----+ | BS/ | PMIPv4 | | + | MN |------| PMA |-----------------------| AGW/ | + +----+ | | | HA | + | | +------+ + +-------+ + + Integrated PMA + + Figure 7: 3GPP2's PMIPv4 Use Case 1 - BS-AGW Interface Mobility + + RAN Core + + +-------+ +------+ + +----+ | AGW/ | PMIPv4 | | + | MN |------| PMA |-----------------------| HA | + +----+ | | | | + | | +------+ + +-------+ + + Integrated PMA + + Figure 8: 3GPP2's PMIPv4 Use Case 2 - AGW-HA Interface Mobility + + The figure below shows a simplified 3GPP2 architecture. For details, + please refer to the 3GPP2 Converged Access Network (CAN) architecture + ([3GPP2]). + + + + + + + + +Leung, et al. Informational [Page 33] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + RAN Core + -----------^------------ -------^------------- + | | | | + V V V V + + +------+ +------+ +-----+ + +----+ | | PMIPv4 | | PMIPv4 | | + | MN |------| BS |------------| AGW |-----------| HA | + +----+ | | | | | | + +------+ +------+ +-----+ + + Figure 9: Simplified 3GPP2 Architecture + + The Proxy Mobile IPv4 usage scenario in 3GPP2 (case 1) is illustrated + in the following diagram: + + +----+ +-------+ +-------+ +------+ + | | | | | | | | + | MN | | BS/ | | HAAA | | AGW/ | + | | | PMA | | | | HA | + +----+ +-------+ +-------+ +------+ + | | | | + | 1a | 1b | | + |<------------->|<----------->| | + | | | | + | 2 | | | + |-------------->| | | + | | 3 | | + | |----------------------->| + | | | | + | | 4 | | + | |<-----------------------| + | 5 | | | + |<--------------| | | + | | | | + | 6 | | | + |<======================================>| + | | | | + + Figure 10: Network Connection Setup (use case 1) + + Description of the steps: + + 1a. MN performs layer 2 establishment with the BS/PMA and performs + access authentication/authorization. During this phase, the MN + runs EAP over Ultra Mobile Broadband (UMB). The BS acts as the + NAS in this phase. + + + + +Leung, et al. Informational [Page 34] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + 1b. The BS exchanges AAA messages with the Home AAA server via the + AR (not shown in the figure) to authenticate the MN. As part of + this step, the AR may download some information about the MN + (e.g., user's profile, handset type, assigned Home Agent + address, and other capabilities of the MN). This information is + passed to the PMA/BS (as necessary) to set up the PMIPv4 tunnel + in the next step(s). + + 2. The MN sends layer 2 signaling messages to the BS/PMA to trigger + the PMIPv4 tunnel setup process. + + 3. Triggered by step 2, the PMA/BS sends a PRRQ to the AGW/HA. The + HA's address is either received at step 1b from the Home AAA + server (HAAA) or is discovered by other means. The PRRQ + contains the Care-of Address (CoA) of the PMA (collocated FA in + this case). The HoA field is set to all zeros (or all ones). + The PRRQ is protected by the method described in this document. + The derivation and distribution of the MN-HA or FA-HA key is + outside the scope of this document. + + 4. The AGW/HA registers the MN's session, assigns a symmetric GRE + key, and returns this key in the PRRP to the BS/PMA. + + 5. The BS/PMA responds back to the MN with a layer 2 signaling + message. + + 6. At this step, the MN is assigned an IP address and is connected + to the network (via the AGW). + + In use case 2, the same procedures are followed except the PMIPv4 + tunnel is established between the AGW and the HA. In this case, GRE + tunneling may not be used. + + + + + + + + + + + + + + + + + + + +Leung, et al. Informational [Page 35] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +11.1. Handover Considerations in 3GPP2 + + There are some special handover considerations in 3GPP2's Proxy + Mobile IPv4 use case. Below is an illustration of the specific use + case: + + +----+ +-------+ +-------+ +-------+ + | | | | | | | | + | MN | | New | | AGW/ | | Old | + | | | PMA/BS| | HA | | PMA/BS| + +----+ +-------+ +-------+ +-------+ + | | | | + | | 1 | | + | |------------->| | + | | | | + | | | | + | | o 2 | + | | | | + | | | | + | | 3 | | + | |<-------------| | + | | | | + | | | | + | | 4 | | + | |<----------------------->| + | | | | + | | | | + | | | o 5 + | | | | + | | | | + + Figure 11: 3GPP2 Registration Revocation for Previous PMA + + Description of the steps: + + 1. MN attaches to the new BS (L2 gets established). There is an + ongoing mobility binding entry (MBE) in the AGW for the MN. The + PMA in the new BS sends a PRRQ to the AGW. + + 2. The AGW receives a Proxy Registration Request for a Mobile Node + and detects that it has an existing Mobility Binding Entry (MBE). + The AGW validates the PRRQ from the new BS and updates the MBE + for the MN. The MBE is kept tentative at this point. + + 3. The AGW sends a Proxy Registration Reply to the new BS. No + Registration Revocation is used in the 3GPP2's use case. + + + + + +Leung, et al. Informational [Page 36] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + 4. A 3GPP2's proprietary PMA movement notification message may be + exchanged between the AGW and the old BS. + + 5. The MBE update with the new BS is committed at this step. + +12. IANA Considerations + + This specification registers 47 for the Proxy Mobile IPv4 + Non-Skippable Extension and 147 for Proxy Mobile IPv4 Skippable + Extension, both of which are described in Section 5. The ranges for + Mobile IPv4 [RFC3344] extension types are defined at + http://www.iana.org. This specification also creates a new subtype + space for the type number of the extensions. The subtype value 1 is + defined for the PMIPv4 Non-Skippable Extension. The subtype values 1 + to 4 are defined for the PMIPv4 Skippable Extension. Similar to the + procedures specified for Mobile IPv4 number spaces, future + allocations from the number space require expert review [RFC5226]. + + The PMIPv4 Per-Node Authentication Method extension defined in + Section 5.1 of this document, introduces a new authentication method + numbering space, where the values from 0 to 2 have been assigned per + this document. Approval of new Access Technology type values are to + be made through IANA Expert Review. + + The PMIPv4 Device ID extension defined in Section 5.3 of this + document, introduces a new ID type numbering space, where the values + from 0 to 4 have been assigned per this document. Approval of new + Access Technology type values are to be made through IANA Expert + Review. + + The PMIPv4 Subscriber ID extension defined in Section 5.4 of this + document, introduces a new ID type numbering space, where the values + from 0 to 1 have been reserved by this document. Approval of new + Access Technology type values are to be made through IANA Expert + Review. + + The PMIPv4 Access Technology Type extension defined in Section 5.5 of + this document, introduces a new technology type numbering space, + where the values from 0 to 8 have been reserved by this document. + Approval of new Access Technology type values are to be made through + IANA Expert Review. + + + + + + + + + + +Leung, et al. Informational [Page 37] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +12.1. Mobile IPv4 Extension Types + + This document introduces the following Mobile IP extension types. + + Name : Proxy Mobile IPv4 Non-Skippable Extension + Type Value : 47 + Section : 5 + + Name : Proxy Mobile IPv4 Skippable Extension + Type Value : 147 + Section : 5 + +12.2. Mobile IPv4 Error Codes + + This document introduces the following error code that can be + returned by the HA in a Proxy Registration Reply. + + Name Value First referenced + ---- ----- ---------------- + PMIP_UNSUPPORTED 149 Section 8.1 of RFC 5563 + PMIP_DISALLOWED 150 Section 8.1 of RFC 5563 + +13. Security Considerations + + The functionality in this document is protected by the authentication + extensions described in RFC 3344 [RFC3344] or IPsec [RFC4301]. Each + PMA needs to have an security association (e.g., MN-HA, FA-HA, IPsec + AH/ESP) with the HA to register the MN's IP address. The security + association can be provisioned by the administrator or dynamically + derived. The dynamic key derivation and distribution for this scheme + is outside the scope of this document. + +14. Acknowledgements + + The authors would like to thank the following individuals for their + review, comments, and suggestions to improve the content of this + document. + + Shahab Sayeedi (Motorola), Alper Yegin (Samsung), Premec Domagoj + (Siemens), Michael Hammer (Cisco), Jun Wang (Qualcomm), Jayshree + Bharatia (Nortel), Semyon Mizikovsky (Alcatel-Lucent), Federico De + Juan Huarte (Alcatel-Lucent), Paula Tjandra (Motorola), Alice Qinxia + (Huawei), Howie Koh (Greenpacket), John Zhao (Huawei), Pete McCann + (Motorola), and Sri Gundavelli (Cisco). + + + + + + + +Leung, et al. Informational [Page 38] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +15. References + +15.1. Normative References + + [3GPP2] "3GPP2 Basic IP Service for Converged Access Network", + X.S0054-100-0 Version 2.0, August 2008. + + [NWG] "WiMAX Forum Network Architecture (Stage 3: Detailed + Protocols and Procedures)" Release 1, Version 1.2.3, + July 2008. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC + 2131, March 1997. + + [RFC3024] Montenegro, G., Ed., "Reverse Tunneling for Mobile IP, + revised", RFC 3024, January 2001. + + [RFC3344] Perkins, C., Ed., "IP Mobility Support for IPv4", RFC + 3344, August 2002. + + [RFC3543] Glass, S. and M. Chandra, "Registration Revocation in + Mobile IPv4", RFC 3543, August 2003. + +15.2. Informative References + + [MIP4GREKEY] Yegani, P., "GRE Key Extension for Mobile IPv4", Work in + Progress, June 2007. + + [MIP4MCBC] Chakrabarti, S., "IPv4 Mobility extension for Multicast + and Broadcast Packets", Work in Progress, November 2007. + + [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, + September 1981. + + [RFC1305] Mills, D., "Network Time Protocol (Version 3) + Specification, Implementation and Analysis", RFC 1305, + March 1992. + + [RFC1332] McGregor, G., "The PPP Internet Protocol Control + Protocol (IPCP)", RFC 1332, May 1992. + + [RFC1661] Simpson, W., Ed., "The Point-to-Point Protocol (PPP)", + STD 51, RFC 1661, July 1994. + + + + + +Leung, et al. Informational [Page 39] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + + [RFC1994] Simpson, W., "PPP Challenge Handshake Authentication + Protocol (CHAP)", RFC 1994, August 1996. + + [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and + H. Levkowetz, Ed., "Extensible Authentication Protocol + (EAP)", RFC 3748, June 2004. + + [RFC4058] Yegin, A., Ed., Ohba, Y., Penno, R., Tsirtsis, G., and + C. Wang, "Protocol for Carrying Authentication for + Network Access (PANA) Requirements", RFC 4058, May 2005. + + [RFC4301] Kent, S. and K. Seo, "Security Architecture for the + Internet Protocol", RFC 4301, December 2005. + + [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC + 4303, December 2005. + + [RFC4332] Leung, K., Patel, A., Tsirtsis, G., and E. Klovning, + "Cisco's Mobile IPv4 Host Configuration Extensions", RFC + 4332, December 2005. + + [RFC4433] Kulkarni, M., Patel, A., and K. Leung, "Mobile IPv4 + Dynamic Home Agent (HA) Assignment", RFC 4433, March + 2006. + + [RFC4436] Aboba, B., Carlson, J., and S. Cheshire, "Detecting + Network Attachment in IPv4 (DNAv4)", RFC 4436, March + 2006. + + [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., + Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", RFC + 5213, August 2008. + + [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an + IANA Considerations Section in RFCs", BCP 26, RFC 5226, + May 2008. + + [RFC5454] Tsirtsis, G., Park, V., and H. Soliman, "Dual-Stack + Mobile IPv4", RFC 5454, March 2009. + + [RFCARP] Plummer, D., "Ethernet Address Resolution Protocol: Or + Converting Network Protocol Addresses to 48.bit Ethernet + Address for Transmission on Ethernet Hardware", STD 37, + RFC 826, November 1982. + + [RFCICMP] Postel, J., "Internet Control Message Protocol", STD 5, + RFC 792, September 1981. + + + + +Leung, et al. Informational [Page 40] + +RFC 5563 WiMAX Forum / 3GPP2 PMIPv4 February 2010 + + +Authors' Addresses + + Kent Leung + Cisco Systems + 170 West Tasman Drive + San Jose, CA 95134 + US + + EMail: kleung@cisco.com + + + Gopal Dommety + Cisco Systems + 170 West Tasman Drive + San Jose, CA 95134 + US + + EMail: gdommety@cisco.com + + + Parviz Yegani + Juniper Networks + 1194 North Mathilda Ave. + Sunnyvale, CA 94089-1206 + + EMail: pyegani@juniper.net + + + Kuntal Chowdhury + Starent Networks + 30 International Place + Tewksbury, MA 01876 + USA + + EMail: kchowdhury@starentnetworks.com + + + + + + + + + + + + + + + + +Leung, et al. Informational [Page 41] + |