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rfc:rfc4584

Network Working Group S. Chakrabarti Request for Comments: 4584 E. Nordmark Category: Informational Sun Microsystems

                                                             July 2006
              Extension to Sockets API for Mobile IPv6

Status of This Memo

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

Copyright Notice

 Copyright (C) The Internet Society (2006).

Abstract

 This document describes data structures and API support for Mobile
 IPv6 as an extension to the Advanced Socket API for IPv6.
 Just as the Advanced Sockets API for IPv6 gives access to various
 extension headers and the ICMPv6 protocol, this document specifies
 the same level of access for Mobile IPv6 components.  It specifies a
 mechanism for applications to retrieve and set information for
 Mobility Header messages, Home Address destination options, and
 Routing Header Type 2 extension headers.  It also specifies the
 common data structures and definitions that might be used by certain
 advanced Mobile IPv6 socket applications.

Chakrabarti & Nordmark Informational [Page 1] RFC 4584 Sockets for API for Mobile IPv6 July 2006

Table of Contents

 1. Introduction ....................................................3
 2. Applicability ...................................................4
 3. Overview ........................................................5
 4. Common Structures and Definitions ...............................6
    4.1. The Mobility Header Data Structures ........................6
         4.1.1. The ip6_mh Structure ................................6
         4.1.2. Binding Refresh Request Mobility Message ............7
         4.1.3. Home Address Test Init (HoTI) Message ...............7
         4.1.4. Care-of Address Test Init (CoTI) Message ............7
         4.1.5. Home Address Test (HOT) Message .....................8
         4.1.6. Care Of Address Test (COT) Message ..................8
         4.1.7. Binding Update Mobility Message .....................8
         4.1.8. Binding Acknowledgement Mobility Message ............9
         4.1.9. Binding Error Mobility Message ......................9
         4.1.10. Mobility Option TLV data structure .................9
         4.1.11. Mobility Option Data Structures ...................10
                4.1.11.1. Binding Refresh Advice ...................10
                4.1.11.2. Alternate Care-of Address ................10
                4.1.11.3. Nonce Indices ............................10
                4.1.11.4. Binding Authorization Data ...............10
    4.2. Mobility Header Constants .................................10
    4.3. IPv6 Home Address Destination Option ......................12
    4.4. Type 2 Routing Header .....................................12
    4.5. New ICMP Messages for Mobile IPv6 .........................13
    4.6. IPv6 Neighbor Discovery Changes ...........................14
 5. Access to Home Address Destination Option and Routing Headers ..15
    5.1. Routing Header Access Functions ...........................17
    5.2. Content of Type 2 Routing Header ..........................18
    5.3. Order of Extension Headers for Home Address
         Destination Options .......................................19
    5.4. Home Address Destination Option Access Functions ..........20
    5.5. Content of Home Address Destination Option ................20
 6. Mobility Protocol Headers ......................................21
    6.1. Receiving and Sending Mobility Header Messages ............21
 7. Protocols File .................................................22
 8. IPv4-Mapped IPv6 Addresses .....................................23
 9. Security Considerations ........................................23
 10. IANA Considerations ...........................................23
 11. Acknowledgements ..............................................23
 12. References ....................................................24
    12.1. Normative References .....................................24
    12.2. Informative References ...................................24

Chakrabarti & Nordmark Informational [Page 2] RFC 4584 Sockets for API for Mobile IPv6 July 2006

1. Introduction

 Mobility Support in IPv6 [2] defines a new Mobility Protocol header,
 a Home Address destination option and a new Routing Header type.  It
 is expected that Mobile IPv6 user-level implementations and some
 special applications will need to access and process these IPv6
 extension headers.  This document is an extension to the existing
 Advanced Sockets API document [1]; it addresses the Advanced IPv6
 Sockets API for these new protocol elements defined by Mobile IPv6.
 The applicability of this API mainly targets user-level applications.
 However, it has also been shown to be useful within some Mobile IPv6
 implementations; for instance, where part of the Mobile IPv6 protocol
 is implemented at user-level and part in the kernel.  It is up to any
 such implementations to architect which part of the Mobile IPv6 and
 IP Security (IPSec) packet processing should be done at the user-
 level in order to meet the design needs of the particular platform
 and operating system.
 The target user-level applications for this socket API are believed
 to be debugging and diagnostic applications and some policy
 applications that would like to receive copies of protocol
 information at the application layer.
 The packet information and access to the extension headers (Routing
 header and Destination options) are specified using the "ancillary
 data" fields that were added to the 4.3BSD Reno sockets API in 1990.
 The reason is that these ancillary data fields are part of the
 Posix.1g standard and should therefore be adopted by most vendors.
 This document is consistent with Advanced Sockets API for IPv6 [1] in
 structure definitions, header files, and function definitions.  Thus,
 the implementors of this API document are assumed to be familiar with
 the data structures, data sending and receiving procedures, and the
 IPv6 extension header access functions described in the Advanced
 Sockets API for IPv6 [1].
 Non-goals
 This document does not address application access to either the
 Authentication Header or the Encapsulating Security Payload header.
 This document also does not address any API that might be necessary
 for Mobile Network [4] specific needs.  Furthermore, note that this
 API document excludes discussion on application-level API.  It
 assumes that address selection socket API [5] takes care of selection
 of care-of address or home address as the source address by the
 application, when source address selection is required due to the
 nature of the application.

Chakrabarti & Nordmark Informational [Page 3] RFC 4584 Sockets for API for Mobile IPv6 July 2006

 Providing mobility "awareness" to applications, such as applications'
 being able to tell whether the host is at home or not, is out of
 scope for this API.

2. Applicability

 This API document can be applied in the following cases:
 1.  User-level debugging and monitoring tools: This socket API is
     useful for accessing Mobility Headers, Home Address destination
     options and Type 2 Routing Headers .  For example, mh-ping might
     be a monitoring tool that can process mobility headers on the
     receiving side to check binding status.
 2.  Partial user-level implementation of Mobile IPv6: We assume that
     some implementations may choose to do the Mobility header
     processing at user level.  In that case, this document recommends
     implementing at least the handling of Home Address destination
     options and Type 2 Routing Header in the main IP processing paths
     in the kernel.  The API can then be used to send and receive the
     Mobility Header packets used for Mobile IPv6 signaling.
 3.  Complete header processing at the kernel-level: Many
     implementations of Mobile IPv6 [2] perform processing of Home
     Address destination options, Type 2 Routing Headers, and Mobility
     headers at the kernel level.  However, the kernel keeps a copy of
     the received extension headers and passes them up to the API,
     which is used by the user-level applications purely for
     monitoring and debugging Mobile IPv6 packets.
 On an IPv6 host that does not implement Mobile IPv6, the IPv6
 specification [3] requires that packets with the Home Address option
 or Type 2 Routing Header (where segments left is non-zero) be dropped
 on receipt.  This means that it is not possible to implement Mobile
 IPv6 as an application on such a system.  Thus, on such a system, the
 applicability of this API is limited to the first case above,
 enabling debugging and monitoring applications (such as tcpdump) to
 parse and interpret Mobile IPv6 packets.

Chakrabarti & Nordmark Informational [Page 4] RFC 4584 Sockets for API for Mobile IPv6 July 2006

3. Overview

 This document can be divided into the following parts:
 1.  Definitions of constants and structures for C programs that
     capture the Mobile IPv6 packet formats on the wire.  A common
     definition of these is useful at least for packet snooping
     applications.  This is captured in Section 4.  In addition,
     Section 4 also defines data structures for Home Address
     destination option, Type 2 Routing Header, and new ICMPv6
     messages related to Mobile IPv6.
 2.  Notes on how to use the IPv6 Advanced API to access Home Address
     options and Type 2 Routing Headers.  This is captured in Section
     5.
 3.  Notes on how user-level applications can observe MH (Mobility
     Header) packets using raw sockets (in Section 6).  The IPv6 RAW
     socket interface described in this document allows applications
     to receive  MH packets whether or not the system's MH processing
     takes place in the "kernel" or at the "user space".
 4.  A name is suggested for IPv6 Mobility Header protocol in /etc/
     protocols (in Section 7).
 All examples in this document omit error checking in favor of
 brevity, as it is following the same style as the Advanced Socket API
 [1].
 Note that many of the functions and socket options defined in this
 document may have error returns that are not defined in this
 document.
 Data types in this document follow the Posix.1g format: intN_t means
 a signed integer of exactly N bits (e.g., int16_t), and uintN_t means
 an unsigned integer of exactly N bits (e.g., uint32_t).
 Once the API specification becomes mature and is deployed, it may be
 formally standardized by a more appropriate body, as has been done
 with the Basic API [6].  However, since this specification largely
 builds upon the Advanced Socket API [1], such standardization would
 make sense only if the Advanced Socket API [1] were also
 standardized.
 The key words "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.

Chakrabarti & Nordmark Informational [Page 5] RFC 4584 Sockets for API for Mobile IPv6 July 2006

4. Common Structures and Definitions

 In this section, the structures are specified in a way so that they
 maximize the probability that the compiler-layout of data structures
 are identical to the packet formats on the wire.  However, ANSI-C
 provides few guarantees about the size and alignment of data
 structures.
 The assumption is that the Advanced Socket API [1] will pass up the
 actual packet content (the wire format) in the buffer and in the
 ancillary data objects.  Thus, if an implementor has to handle a
 system where the ANSI-C compiler does not and can not lay out these
 structures to match the wire formats in RFC 3775 [2], the structures
 defined by this API can not be supported on such a system.
 The constants and structures shown below are in network byte order,
 so an application needs to perform the appropriate byte order
 conversion (ntohs(), etc) when necessary.
 The structures and constants below will be included when the (new)
 header file is included : <netinet/ip6mh.h>

4.1. The Mobility Header Data Structures

4.1.1. The ip6_mh Structure

 The following structure is defined as a result of including
 <netinet/ip6mh.h>.  This is the fixed part of the Mobility Header.
 Different Mobility message types are defined in Mobile IPv6 [2].  For
 portability and alignment reasons, each mobility message type
 includes the mobility header fields instead of including the ip6_mh
 structure, followed by the message-specific fields.
    struct  ip6_mh {
        uint8_t    ip6mh_proto;   /* NO_NXTHDR by default */
        uint8_t    ip6mh_hdrlen;  /* Header Len in unit of 8 Octets
                                     excluding the first 8 Octets */
        uint8_t    ip6mh_type;    /* Type of Mobility Header */
        uint8_t    ip6mh_reserved;   /* Reserved */
        uint16_t   ip6mh_cksum;   /* Mobility Header Checksum */
        /* Followed by type specific messages */
    };

Chakrabarti & Nordmark Informational [Page 6] RFC 4584 Sockets for API for Mobile IPv6 July 2006

4.1.2. Binding Refresh Request Mobility Message

    struct  ip6_mh_binding_request {
        uint8_t    ip6mhbr_proto;
        uint8_t    ip6mhbr_hdrlen;
        uint8_t    ip6mhbr_type;
        uint8_t    ip6mhbr_reserved;
        uint16_t   ip6mhbr_cksum;
        uint16_t   ip6mhbr_reserved2;
        /* Followed by optional Mobility Options */
    };

4.1.3. Home Address Test Init (HoTI) Message

    struct   ip6_mh_home_test_init {
       uint8_t    ip6mhhti_proto;
       uint8_t    ip6mhhti_hdrlen;
       uint8_t    ip6mhhti_type;
       uint8_t    ip6mhhti_reserved;
       uint16_t   ip6mhhti_cksum;
       uint16_t   ip6mhhti_reserved2;
       uint32_t   ip6mhhti_cookie[2]; /* 64 bit Cookie by MN */
       /* Followed by optional Mobility Options */
    };

4.1.4. Care-of Address Test Init (CoTI) Message

    struct   ip6_mh_careof_test_init {
       uint8_t    ip6mhcti_proto;
       uint8_t    ip6mhcti_hdrlen;
       uint8_t    ip6mhcti_type;
       uint8_t    ip6mhcti_reserved;
       uint16_t   ip6mhcti_cksum;
       uint16_t   ip6mhcti_reserved2;
       uint32_t   ip6mhcti_cookie[2]; /* 64 bit Cookie by MN */
       /* Followed by optional Mobility Options */
    };

Chakrabarti & Nordmark Informational [Page 7] RFC 4584 Sockets for API for Mobile IPv6 July 2006

4.1.5. Home Address Test (HOT) Message

     struct  ip6_mh_home_test {
        uint8_t    ip6mhht_proto;
        uint8_t    ip6mhht_hdrlen;
        uint8_t    ip6mhht_type;
        uint8_t    ip6mhht_reserved;
        uint16_t   ip6mhht_cksum;
        uint16_t   ip6mhht_nonce_index;
        uint32_t   ip6mhht_cookie[2];    /* Cookie from HOTI msg */
        uint32_t   ip6mhht_keygen[2];  /* 64 Bit Key by CN */
        /* Followed by optional Mobility Options */
    };

4.1.6. Care Of Address Test (COT) Message

    struct  ip6_mh_careof_test {
       uint8_t    ip6mhct_proto;
       uint8_t    ip6mhct_hdrlen;
       uint8_t    ip6mhct_type;
       uint8_t    ip6mhct_reserved;
       uint16_t   ip6mhct_cksum;
       uint16_t   ip6mhct_nonce_index;
       uint32_t   ip6mhct_cookie[2]; /* Cookie from COTI message */
       uint32_t   ip6mhct_keygen[2];  /* 64bit key by CN */
       /* Followed by optional Mobility Options */
    };

4.1.7. Binding Update Mobility Message

    struct ip6_mh_binding_update {
        uint8_t     ip6mhbu_proto;
        uint8_t     ip6mhbu_hdrlen;
        uint8_t     ip6mhbu_type;
        uint8_t     ip6mhbu_reserved;
        uint16_t    ip6mhbu_cksum;
        uint16_t    ip6mhbu_seqno;      /* Sequence Number */
        uint16_t    ip6mhbu_flags;
        uint16_t    ip6mhbu_lifetime; /* Time in unit of 4 sec */
        /* Followed by optional Mobility Options */
    };
     /* Binding Update Flags, in network byte-order */
     #define IP6_MH_BU_ACK    0x8000  /* Request a binding ack */
     #define IP6_MH_BU_HOME   0x4000  /* Home Registration */
     #define IP6_MH_BU_LLOCAL 0x2000  /* Link-local compatibility */
     #define IP6_MH_BU_KEYM   0x1000  /* Key management mobility  */

Chakrabarti & Nordmark Informational [Page 8] RFC 4584 Sockets for API for Mobile IPv6 July 2006

4.1.8. Binding Acknowledgement Mobility Message

    struct  ip6_mh_binding_ack {
       uint8_t   ip6mhba_proto;
       uint8_t   ip6mhba_hdrlen;
       uint8_t   ip6mhba_type;
       uint8_t   ip6mhba_reserved;
       uint16_t  ip6mhba_cksum;
       uint8_t   ip6mhba_status;    /* Status code */
       uint8_t   ip6mhba_flags;
       uint16_t  ip6mhba_seqno;
       uint16_t  ip6mhba_lifetime;
       /* Followed by optional Mobility Options */
    };
     /* Binding Acknowledgement Flags */
     #define IP6_MH_BA_KEYM       0x80  /* Key management mobility */

4.1.9. Binding Error Mobility Message

     struct   ip6_mh_binding_error {
        uint8_t   ip6mhbe_proto;
        uint8_t   ip6mhbe_hdrlen;
        uint8_t   ip6mhbe_type;
        uint8_t   ip6mhbe_reserved;
        uint16_t  ip6mhbe_cksum;
        uint8_t   ip6mhbe_status;  /* Error Status */
        uint8_t   ip6mhbe_reserved2;
        struct in6_addr ip6mhbe_homeaddr;
        /* Followed by optional Mobility Options */
      };

4.1.10. Mobility Option TLV data structure

    struct   ip6_mh_opt {
       uint8_t    ip6mhopt_type;   /* Option Type */
       uint8_t    ip6mhopt_len;    /* Option Length */
       /* Followed by variable length Option Data in bytes */
    };

Chakrabarti & Nordmark Informational [Page 9] RFC 4584 Sockets for API for Mobile IPv6 July 2006

4.1.11. Mobility Option Data Structures

4.1.11.1. Binding Refresh Advice

    struct ip6_mh_opt_refresh_advice {
        uint8_t  ip6mora_type;
        uint8_t  ip6mora_len;
        uint16_t ip6mora_interval; /* Refresh interval in 4 sec */
    };

4.1.11.2. Alternate Care-of Address

    struct ip6_mh_opt_altcoa {
        uint8_t ip6moa_type;
        uint8_t ip6moa_len;
        struct in6_addr ip6moa_addr; /* Alternate CoA */
    };

4.1.11.3. Nonce Indices

    struct ip6_mh_opt_nonce_index {
        uint8_t ip6moni_type;
        uint8_t ip6moni_len;
        uint16_t ip6moni_home_nonce;
        uint16_t ip6moni_coa_nonce;
    };

4.1.11.4. Binding Authorization Data

    struct ip6_mh_opt_auth_data {
        uint8_t ip6moad_type;
        uint8_t ip6moad_len;
        uint8_t ip6moad_data[12];
    };

4.2. Mobility Header Constants

 IPv6 Next Header Value for Mobility:
    <netinet/in.h>
    #define IPPROTO_MH       135 /* IPv6 Mobility Header: IANA */

Chakrabarti & Nordmark Informational [Page 10] RFC 4584 Sockets for API for Mobile IPv6 July 2006

    Mobility Header Message Types:
    <netinet/ip6mh.h>
    #define IP6_MH_TYPE_BRR       0   /* Binding Refresh Request */
    #define IP6_MH_TYPE_HOTI      1   /* HOTI Message   */
    #define IP6_MH_TYPE_COTI      2   /* COTI Message  */
    #define IP6_MH_TYPE_HOT       3   /* HOT Message   */
    #define IP6_MH_TYPE_COT       4   /* COT Message  */
    #define IP6_MH_TYPE_BU        5   /* Binding Update */
    #define IP6_MH_TYPE_BACK      6   /* Binding ACK */
    #define IP6_MH_TYPE_BERROR    7   /* Binding Error */
 Mobility Header Message Option Types:
 <netinet/ip6mh.h>
    #define  IP6_MHOPT_PAD1       0x00  /* PAD1 */
    #define  IP6_MHOPT_PADN       0x01  /* PADN */
    #define  IP6_MHOPT_BREFRESH   0x02  /* Binding Refresh */
    #define  IP6_MHOPT_ALTCOA     0x03  /* Alternate COA */
    #define  IP6_MHOPT_NONCEID    0x04  /* Nonce Index */
    #define  IP6_MHOPT_BAUTH      0x05  /* Binding Auth Data */
 Status values accompanied with Mobility Binding Acknowledgement:
 <netinet/ip6mh.h>
    #define IP6_MH_BAS_ACCEPTED          0   /* BU accepted */
    #define IP6_MH_BAS_PRFX_DISCOV       1   /* Accepted, but prefix
                                                discovery Required */
    #define IP6_MH_BAS_UNSPECIFIED       128 /* Reason unspecified */
    #define IP6_MH_BAS_PROHIBIT          129 /* Administratively
                                                prohibited */
    #define IP6_MH_BAS_INSUFFICIENT      130 /* Insufficient
                                                resources */
    #define IP6_MH_BAS_HA_NOT_SUPPORTED  131 /* HA registration not
                                                supported */
    #define IP6_MH_BAS_NOT_HOME_SUBNET   132  /* Not Home subnet */
    #define IP6_MH_BAS_NOT_HA            133  /* Not HA for this
                                                 mobile node */
    #define IP6_MH_BAS_DAD_FAILED        134  /* DAD failed */
    #define IP6_MH_BAS_SEQNO_BAD         135  /* Sequence number out
                                                 of range */

Chakrabarti & Nordmark Informational [Page 11] RFC 4584 Sockets for API for Mobile IPv6 July 2006

    #define IP6_MH_BAS_HOME_NI_EXPIRED   136  /* Expired Home nonce
                                                 index */
    #define IP6_MH_BAS_COA_NI_EXPIRED    137  /* Expired Care-of
                                                 nonce index */
    #define IP6_MH_BAS_NI_EXPIRED        138  /* Expired Nonce
                                                 Indices */
    #define IP6_MH_BAS_REG_NOT_ALLOWED   139  /* Registration type
                                                 change disallowed */
 Status values for the Binding Error mobility messages:
 <netinet/ip6mh.h>
    #define IP6_MH_BES_UNKNOWN_HAO    1 /* Unknown binding for HOA */
    #define IP6_MH_BES_UNKNOWN_MH     2 /* Unknown MH Type */

4.3. IPv6 Home Address Destination Option

    Due to alignment issues in the compiler, and the alignment
    requirements for this option, the included IPv6 address must be
    specified as an array of 16 octets.
    <netinet/ip6.h>
    /* Home Address Destination Option */
    struct ip6_opt_home_address {
         uint8_t           ip6oha_type;
         uint8_t           ip6oha_len;
         uint8_t           ip6oha_addr[16];   /* Home Address */
    };
 Option Type Definition:
 #define IP6OPT_HOME_ADDRESS        0xc9    /* 11 0 01001 */

4.4. Type 2 Routing Header

    <netinet/ip6.h>
    /* Type 2 Routing header for Mobile IPv6 */
    struct ip6_rthdr2 {
         uint8_t  ip6r2_nxt;       /* next header */
         uint8_t  ip6r2_len;       /* length : always 2 */
         uint8_t  ip6r2_type;      /* always 2 */
         uint8_t  ip6r2_segleft;   /* segments left: always 1 */
         uint32_t ip6r2_reserved;  /* reserved field */
         struct in6_addr ip6r2_homeaddr;  /* Home Address */
    };

Chakrabarti & Nordmark Informational [Page 12] RFC 4584 Sockets for API for Mobile IPv6 July 2006

4.5. New ICMP Messages for Mobile IPv6

 ICMP message types and definitions for Mobile IPv6 are defined in
 <netinet/icmp6.h>.
    #define MIP6_HA_DISCOVERY_REQUEST    144
    #define MIP6_HA_DISCOVERY_REPLY      145
    #define MIP6_PREFIX_SOLICIT          146
    #define MIP6_PREFIX_ADVERT           147
 The following data structures can be used for the ICMP message types
 discussed in Sections 6.5 through 6.8 in the base Mobile IPv6 [2]
 specification.
    struct mip6_dhaad_req {    /* Dynamic HA Address Discovery */
           struct  icmp6_hdr   mip6_dhreq_hdr;
    };
    #define  mip6_dhreq_type      mip6_dhreq_hdr.icmp6_type
    #define  mip6_dhreq_code      mip6_dhreq_hdr.icmp6_code
    #define  mip6_dhreq_cksum     mip6_dhreq_hdr.icmp6_cksum
    #define  mip6_dhreq_id        mip6_dhreq_hdr.icmp6_data16[0]
    #define  mip6_dhreq_reserved  mip6_dhreq_hdr.icmp6_data16[1]
    struct mip6_dhaad_rep {    /* HA Address Discovery Reply */
           struct icmp6_hdr   mip6_dhrep_hdr;
           /* Followed by Home Agent IPv6 addresses */
    };
    #define  mip6_dhrep_type      mip6_dhrep_hdr.icmp6_type
    #define  mip6_dhrep_code      mip6_dhrep_hdr.icmp6_code
    #define  mip6_dhrep_cksum     mip6_dhrep_hdr.icmp6_cksum
    #define  mip6_dhrep_id        mip6_dhrep_hdr.icmp6_data16[0]
    #define  mip6_dhrep_reserved  mip6_dhrep_hdr.icmp6_data16[1]
    struct mip6_prefix_solicit {   /* Mobile Prefix Solicitation */
           struct icmp6_hdr     mip6_ps_hdr;
    };
    #define  mip6_ps_type          mip6_ps_hdr.icmp6_type
    #define  mip6_ps_code          mip6_ps_hdr.icmp6_code
    #define  mip6_ps_cksum         mip6_ps_hdr.icmp6_cksum
    #define  mip6_ps_id            mip6_ps_hdr.icmp6_data16[0]
    #define  mip6_ps_reserved      mip6_ps_hdr.icmp6_data16[1]

Chakrabarti & Nordmark Informational [Page 13] RFC 4584 Sockets for API for Mobile IPv6 July 2006

    struct mip6_prefix_advert {  /* Mobile Prefix Advertisements */
           struct  icmp6_hdr   mip6_pa_hdr;
            /* Followed by one or more PI options */
    };
    #define  mip6_pa_type            mip6_pa_hdr.icmp6_type
    #define  mip6_pa_code            mip6_pa_hdr.icmp6_code
    #define  mip6_pa_cksum           mip6_pa_hdr.icmp6_cksum
    #define  mip6_pa_id              mip6_pa_hdr.icmp6_data16[0]
    #define  mip6_pa_flags_reserved  mip6_pa_hdr.icmp6_data16[1]
    /* Mobile Prefix Advertisement Flags in network-byte order */
     #define  MIP6_PA_FLAG_MANAGED    0x8000
     #define  MIP6_PA_FLAG_OTHER      0x4000
 Prefix options are defined in IPv6 Advanced Socket API [1].  The
 Mobile IPv6 Base specification [2] describes the modified behavior in
 the 'Modifications to IPv6 Neighbor Discovery' section.  Prefix
 Options for Mobile IP are defined in the following section.

4.6. IPv6 Neighbor Discovery Changes

 IPv6 Neighbor Discovery changes are also defined in
 <netinet/icmp6.h>.
    New 'Home Agent' flag in router advertisement:  #define
    ND_RA_FLAG_HOMEAGENT   0x20  /* Home Agent flag in RA */
    New Router flag with prefix information of the home agent:
    #define  ND_OPT_PI_FLAG_ROUTER  0x20  /* Router flag in PI */
 As per the Mobile IPv6 specification [2], Section 7.2, a Home Agent
 MUST include at least one prefix option with the Router Address (R)
 bit set.  Advanced Socket API [1] defines data structure for prefix
 option as follows:
    struct nd_opt_prefix_info {    /* prefix information */
         uint8_t   nd_opt_pi_type;
         uint8_t   nd_opt_pi_len;
         uint8_t   nd_opt_pi_prefix_len;
         uint8_t   nd_opt_pi_flags_reserved;
         uint32_t  nd_opt_pi_valid_time;
         uint32_t  nd_opt_pi_preferred_time;
         uint32_t  nd_opt_pi_reserved2;
         struct in6_addr  nd_opt_pi_prefix;
    };

Chakrabarti & Nordmark Informational [Page 14] RFC 4584 Sockets for API for Mobile IPv6 July 2006

 New advertisement interval option and home agent information options
 are defined in Mobile IPv6 [2] base specification.
    struct nd_opt_adv_interval { /* Advertisement interval option */
         uint8_t        nd_opt_ai_type;
         uint8_t        nd_opt_ai_len;
         uint16_t       nd_opt_ai_reserved;
         uint32_t       nd_opt_ai_interval;
    };
 The option types for the new Mobile IPv6 specific options:
    #define  ND_OPT_ADV_INTERVAL    7     /* Adv Interval Option  */
    #define  ND_OPT_HA_INFORMATION  8     /* HA Information option */
    struct nd_opt_homeagent_info {  /* Home Agent information */
       uint8_t        nd_opt_hai_type;
       uint8_t        nd_opt_hai_len;
       uint16_t       nd_opt_hai_reserved;
       uint16_t       nd_opt_hai_preference;
       uint16_t       nd_opt_hai_lifetime;
    };

5. Access to Home Address Destination Option and Routing Headers

 Applications that need to be able to access Home Address destination
 option and Type 2 Routing Header information can do so by setting the
 appropriate setsockopt option and using ancillary data objects.  The
 order of extension headers is defined in Mobile IPv6 [2] when an IPv6
 packet with a Home Address Destination Option is sent with other
 possible extension headers.  Section 5.3 elaborates on the extension
 header order when all possible cases are present.
 This document does not recommend that the user-level program set the
 Home Address destination option or Type 2 Routing Header option;
 however, for clarity it defines the order of extension headers.  See
 Section 2 of this document for appropriate usage of sending and
 receiving of Home Address destination options and Type 2 Routing
 Header extension headers.
 This document defines a new socket option, IPV6_MIPDSTOPTS for
 sending Home Address destination options.  In order to receive a Home
 Address destination option or Type 2 Route Header, applications must
 call setsockopt() to turn on the corresponding flag as described in
 IPv6 Advanced Socket API [1] ( for brevity, error checking is not
 performed in the examples):

Chakrabarti & Nordmark Informational [Page 15] RFC 4584 Sockets for API for Mobile IPv6 July 2006

    int  on = 1;
    setsockopt(fd, IPPROTO_IPV6, IPV6_RECVRTHDR,    &on, sizeof(on));
    setsockopt(fd, IPPROTO_IPV6, IPV6_RECVDSTOPTS,
                 &on, sizeof(on));
 When any of these options are enabled, the corresponding data is
 returned as control information by recvmsg(), as one or more
 ancillary data objects.  Receiving the above information for TCP
 applications is not defined in this document (see Section 4.1 of
 Advanced Sockets API for IPv6 [1]).
 Note that if the IP implementation on the host does not implement the
 handling of Type 2 Routing Headers or Home Address options, per RFC
 2460 [3] the IP stack is required to drop the packet.  Thus,
 receiving Home Address destination option and Type 2 Routing Header
 at the application layer requires implementation of respective
 extension headers at the IP layer in the kernel, as defined in
 RFC3775 [2].
 For receiving the Home Address destination option header, the Mobile
 IPv6 implementation SHOULD follow the initial processing rules of the
 Home Address destination option (Section 9.3.1 of Mobile IPv6 [2])
 before passing the information to the API level.  This includes
 initial processing of IPSec authentication data in a packet when it
 exists.  Each Destination options header is returned as one ancillary
 data object described by a cmsghdr structure with cmsg_level set to
 IPPROTO_IPV6 and cmsg_type set to IPV6_DSTOPTS.
 For sending the Home Address destination option, ancillary data can
 be used to specify the option content for a single datagram.  This
 applies only to datagram and raw sockets, not to TCP sockets.  The
 Advanced API [1] document restricts one IPV6_xxx ancillary data
 object for a particular extension header in the control buffer.
 Thus, there would be a single ancillary data object for the Home
 address destination option in an ancillary data buffer.  If multiple
 destination options are present, then the header order should be in
 compliance with Section 6.3 and 9.3.2 of the Mobile IPv6 [2] base
 specification.
 For TCP data packets with the Home Address destination option, the
 "sticky" option may be used for all transmitted packets.  The
 application can remove the sticky Home Destination option header by
 calling setsockopt() for IPV6_MIPDSTOPTS with a zero option length.
 Note that Section 2 of this document does not encourage setting the
 Home Address destination option at the user level.  A Mobile IPv6
 implementation should set and process the Home Address destination

Chakrabarti & Nordmark Informational [Page 16] RFC 4584 Sockets for API for Mobile IPv6 July 2006

 option and Routing Header Type 2 at the kernel level.  The setting of
 Routing Header Type 2 and the Home Address destination option are
 described in this document for completeness and flexibility to use
 them in the future, if there is a need.
 The following socket option parameters and cmsghdr fields may be used
 for sending (although not a recommended usage):
    opt level/    optname/          optval/
    cmsg_level    cmsg_type         cmsg_data[]
    ------------  ------------      ------------------------
    IPPROTO_IPV6  IPV6_MIPDSTOPTS      ip6_dest structure
    IPPROTO_IPV6  IPV6_RTHDR           ip6_rthdr structure
 Some IPv6 implementations may support "sticky" options [1] for the
 IPv6 destination option for datagram and RAW sockets.
 Behavior of Legacy IPv6 Socket Applications:
 Legacy IPv6 applications/implementations using the Advanced Socket
 API [1] mechanisms, upon receiving Home Address destination options
 or Routing headers(Type 2), will discard the packet as per Sections
 4.2 and 4.4 of IPV6 Protocol [3] specification, respectively;
 otherwise, they should properly handle the Home Address destination
 option and the Routing Header Type 2 specified in this document.

5.1. Routing Header Access Functions

 IPV6 Protocol [3] defines a Routing header extension header for Type
 0.  Thus, in order to access the IPv6 Routing header Type 2 extension
 header, one MUST use type = 2 and segment = 1.  The following
 existing functions defined in Advanced API for IPv6 Sockets [1] are
 supported for Mobile IPv6 applications for sending and receiving
 Routing Header Type 2 headers:
 For Sending:
   size_t inet6_rth_space(int type, int segments);
   void *inet6_rth_init(void *bp, int bp_len, int type, int segments);
   int inet6_rth_add(void *bp, const struct in6_addr *addr);
 For Receiving:
    int inet6_rth_segments(const void *bp);
    struct in6_addr *inet6_rth_getaddr(const void *bp, int index);
 NOTE: Reversing operation is not possible using the Route Header Type
 2 extension header.  Thus, inet6_rth_reverse() is not used.

Chakrabarti & Nordmark Informational [Page 17] RFC 4584 Sockets for API for Mobile IPv6 July 2006

 Detailed descriptions and examples of accessing an IPv6 Routing
 Header are discussed in the Advanced Sockets API for IPv6 [1].
 However, Section 7 of Advanced API for IPv6 Sockets [1] indicates
 that multiple types of routing headers can be received as multiple
 ancillary data objects to the application (with cmsg_type set to
 IPV6_RTHDR).  Currently, there are no API functions defined to return
 the routing header type.  However, this document does not define a
 helper function, since it is easy to access the Routing Header Type
 field just as easily as the ip6r_segleft field.  An excerpt of a code
 sample is provided for extracting the type of the received routing
 header:
    if (msg.msg_controllen != 0 &&
        cmsgptr->cmsg_level == IPPROTO_IPV6 &&
        cmsgptr->cmsg_type == IPV6_RTHDR) {
            struct in6_addr *in6;
            char asciiname[INET6_ADDRSTRLEN];
            struct ip6_rthdr *rthdr;
            int    segments, route_type;
            rthdr = (struct ip6_rthdr *)extptr;
            segments = inet6_rth_segments(extptr);
            printf("route (%d segments, %d left): ",
                segments, rthdr->ip6r_segleft);
            route_type = rthdr->ip6r_type;
            if (route_type == 2) {
                    printf ("Routing header Type 2 present\n");
            }
    }

5.2. Content of Type 2 Routing Header

 It is recommended that no portable applications send Type 2 Routing
 Header ancillary data from the application layer, since many
 implementations take care of that at the kernel layer and may not
 support the API for sending Type 2 Routing Header.
 Mobile IPv6 [2] defines the Type 2 Routing Header to allow the packet
 to be routed directly from a correspondent to the mobile node's
 care-of address.  The mobile node's care-of address is inserted into
 the IPv6 Destination Address field.  Once the packet arrives at the
 care-of address, the mobile node retrieves its home address from the
 routing header, and this is used as the final destination address for
 the received IPv6 packet.

Chakrabarti & Nordmark Informational [Page 18] RFC 4584 Sockets for API for Mobile IPv6 July 2006

 For user-level applications that receive Type 2 Routing Header,
 inet6_rth_getaddr() returns the care-of address or on-the-wire
 destination address of the received packet.  This complies with the
 existing Routing header Type=0 processing for IPv6 [1].
 Thus, on the receive side, the socket application will always receive
 data packets at its original home address.  The implementations are
 responsible for processing the Type 2 Routing Header packet as per
 Mobile IPv6 RFC [2] before passing the Type 2 Routing Header
 information to the Socket API.
 If a pure IPv6 [3] system receives the Routing Header Type 2 packets,
 it will follow the process described in Section 4.4 of the IPv6 [3]
 base specification.

5.3. Order of Extension Headers for Home Address Destination Options

 Section 6.3 of Mobile IPV6 [2] defines the extension header order for
 the Home address destination option.
    Routing Header
    Home Address Destination Option
    Fragment Header
    AH/ESP Header
 IPv6 [3] specifies that the destination header can be either before
 the Routing header or after the AH/ESP header if they are all
 present.
 Thus, when the Home Address destination option is present along with
 other extension headers, the order will be:
    Hop-by-Hop Options header
    Destination Options header
    Routing header
    Destination Options [Home Address Option]
    Fragment header
    Authentication header
    Encapsulating Security Payload header
    Destination Options header
    upper-layer header
 Any user-level implementation or application that sends the Home
 address destination option through ancillary data objects should
 follow the order extension header defined in this document when using
 IPV6_MIPDSTOPTS socket options.

Chakrabarti & Nordmark Informational [Page 19] RFC 4584 Sockets for API for Mobile IPv6 July 2006

5.4. Home Address Destination Option Access Functions

 The application must enable the IPV6_RECVDSTOPTS socket option in
 order to receive the Home Address destination option (error checking
 is not performed in the example for brevity):
    int  on = 1;
    setsockopt(fd, IPPROTO_IPV6, IPV6_RECVDSTOPTS, &on, sizeof(on));
 Each Destination option header is returned as one ancillary data
 object described by a cmsghdr structure, with cmsg_level set to
 IPPROTO_IPV6 and cmsg_type set to IPV6_DSTOPTS.
 The received side Home Address destination option is further
 processed by calling the inet6_opt_next(), inet6_opt_find(), and
 inet6_opt_get_value() functions as defined in Advanced API for IPv6
 sockets [1].
 This document assumes that portable Mobile IPv6 applications will not
 send a Home Address Destination Option from the application level, as
 the Mobile IPv6 implementation underneath takes care of sending the
 Home Address option and the routing header type 2 at the kernel.
 However, some embedded software implementations may implement the
 IPv6 packet processing/sending at the user-level; those
 implementations may choose to provide the API support for sending a
 home-address option at the application layer.  In this case, the Home
 Address destination options are normally constructed by using the
 inet6_opt_init(), inet6_opt_append(), inet6_opt_finish(), and
 inet6_opt_set_val() functions, described in Section 10 of the
 Advanced sockets API for IPv6 [1].

5.5. Content of Home Address Destination Option

 The received ancillary data object for the Home Address destination
 option SHOULD contain the care-of address of the mobile node.  It is
 assumed that the initial processing of the Home Address destination
 option will verify the validity of the home address, as described in
 Sections 6.3 and 9.5 of the Mobile IPv6 Specification [2], and swap
 the source address of the packet (COA) with the contents of Home
 Address destination option.
 Note that whether or not these new APIs are used, the sender's home
 address is contained in the source address (which is passed to the
 application using the socket-level functions recvfrom(), recvmsg(),
 accept(), and getpeername()).  This is necessary for:

Chakrabarti & Nordmark Informational [Page 20] RFC 4584 Sockets for API for Mobile IPv6 July 2006

    maintaining consistency between simple user-level applications
    running between mobile nodes and the diagnostic applications on
    the home agent or correspondent node that use this API;
    obtaining the COA address of the mobile node when the Home Address
    destination option is used; and
    maintaining consistency of existing IPv6 Socket APIs and
    processing of the Home Address destination option.
 If an implementation supports send-side Home Address destination API,
 then it must follow the same rule for data content as specified in
 Mobile IPv6 RFC [2] for sending a home-address option.  Thus, the
 home-address option will contain the home address, and the
 implementation will use the care-of address as the source address of
 the outgoing packet.  If the implementation uses IPSec, then it
 should use the content of Home Address destination option as the
 source address of the packet for security association.  Note that
 regular user applications must not set the home address destination
 option.

6. Mobility Protocol Headers

 Mobile IPv6 [2] defines a new IPv6 protocol header to carry mobility
 messages between Mobile Nodes, Home Agents and Correspondent Nodes.
 These protocol headers carry Mobile IPv6 Binding messages as well as
 Return Routability [2] messages.  Currently the specification [2]
 does not allow transport packets (piggybacking) along with the
 mobility messages.  Thus the mobility protocol header can be accessed
 through an IPv6 RAW socket.  An IPv6 RAW socket that is opened for
 protocol IPPROTO_MH should always be able to see all the MH (Mobility
 Header) packets.  It is possible that future applications may
 implement part of Mobile IPv6 signal processing at the application
 level.  Having a RAW socket interface may also enable an application
 to execute the Return Routability protocol or other future
 authentication protocol involving the mobility header at the user-
 level.

6.1. Receiving and Sending Mobility Header Messages

 This specification recommends that the IPv6 RAW sockets mechanism
 send and receive Mobility Header (MH) packets.  The behavior is
 similar to ICMPV6 processing, where the kernel passes a copy of the
 mobility header packet to the receiving socket.  Depending on the
 implementation, the kernel may process the mobility header in
 addition to passing the mobility header to the application.  In order
 to comply with the restriction in the Advanced Sockets API for IPv6
 [1], applications should set the IPV6_CHECKSUM socket option with

Chakrabarti & Nordmark Informational [Page 21] RFC 4584 Sockets for API for Mobile IPv6 July 2006

 IPPROTO_MH protocol RAW Sockets.  A Mobile IPv6 implementation that
 supports the Mobile IPv6 API must implement Mobility Header API
 checksum calculations by default at the kernel for both incoming and
 outbound paths.  A Mobile IPv6 implementation must not return error
 on the IPV6_CHECKSUM socket option setting, even if the socket option
 is a NO-OP function for that implementation because it verifies the
 checksum at the kernel level.  The Mobility Header checksum procedure
 is described in the Mobile IPv6 Protocol [2] specification.  Again,
 for application portability it is recommended that the applications
 set the IPV6_CHECKSUM socket option along with the RAW sockets for
 IPPROTO_MH protocol.
 As an example, a program that wants to send or receive a mobility
 header protocol(MH) could open a socket as follows (for brevity, the
 error checking is not performed in the example below):
    fd = socket(AF_INET6, SOCK_RAW, IPPROTO_MH);
    int offset = 4;
    setsockopt(fd, IPPROTO_IPV6, IPV6_CHECKSUM, &offset,
         sizeof(offset));
 For example, if an implementation likes to handle HOTI/HOT and COTI/
 COT message processing, it can do so by using IPv6 RAW Sockets for
 IPPROTO_MH at the application layer.  The same application may also
 set the IPV6_RECVDSTOPTS socket option for receiving Home Address
 destination option in a binding update [2] from the mobile node.
 IPv6 RAW sockets are described in Section 3 of the IPv6 Advanced
 Socket API [1] specification.  All data sent and received via raw
 sockets must be in network byte order.  The data structures that are
 defined in this document are in network byte order, and they are
 believed to be supported by most compilers to hold packet formats
 directly for transmission on the wire.
 The usual send/recv functions for datagram should be used for the
 Mobile IPv6 RAW sockets in order to send and receive data,
 respectively.

7. Protocols File

 Many hosts provide the file /etc/protocols, which contains the names
 of the various IP protocols and their protocol numbers.  The protocol
 numbers are obtained through function getprotoXXX() functions.
 The following addition should be made to the /etc/protocols file, in
 addition to what is defined in Section 2.4 of the Advanced Sockets
 API for IPv6 [1].

Chakrabarti & Nordmark Informational [Page 22] RFC 4584 Sockets for API for Mobile IPv6 July 2006

 The protocol number for Mobility Header:
 (http://www.iana.org/assignments/protocol-numbers)
    ipv6-mh           135      # Mobility Protocol Header

8. IPv4-Mapped IPv6 Addresses

 The various socket options and ancillary data specifications defined
 in this document apply only to true IPv6 sockets.  It is possible to
 create an IPv6 socket that actually sends and receives IPv4 packets,
 using IPv4-mapped IPv6 addresses, but the mapping of the options
 defined in this document to an IPv4 datagram is beyond the scope of
 this document.  The above statement is in compliance with Section 13
 of the IPv6 Socket API [1].

9. Security Considerations

 The setting of the Home Address Destination option and Route Header
 Type 2 IPV6_RTHDR socket option may not be allowed at the application
 level in order to prevent denial-of-service attacks or man-in-the-
 middle attacks by hackers.  Sending and receiving of mobility header
 messages are possible by IPv6 RAW sockets.  Thus, it is assumed that
 this operation is only possible by privileged users.  However, this
 API does not prevent the existing security threat from a hacker
 sending a bogus mobility header or other IPv6 packets using the Home
 Address option and Type 2 Routing Header extensions.

10. IANA Considerations

 This document does not define a new protocol.  However, it uses the
 Mobility Header Protocol for IPv6 to define an API for the
 /etc/protocols file. (ref: http://www.iana.org/assignments/protocol-
 numbers)

11. Acknowledgements

 Thanks to Brian Haley for the thorough review of this document and
 many helpful comments.  Keiichi Shima, Alexandru Petrescu, Ryuji
 Wakikawa, Vijay Devarapalli, Jim Bound, Suvidh Mathur, Karen Nielsen,
 Mark Borst, Vladislav Yasevich, and other mobile-ip working group
 members provided valuable input.  Antti Tuominen suggested the
 routing header type function for this API document.  During IESG
 review, Bill Fenner suggested accessing the routing header type
 directly for being consistent with RFC3542.  A new socket option for
 Home Address Destination Option is added per Bill Fenner's suggestion
 for clarity of extension header orders.  Thanks to Thomas Narten and
 Jari Arkko for the review of this document.

Chakrabarti & Nordmark Informational [Page 23] RFC 4584 Sockets for API for Mobile IPv6 July 2006

12. References

12.1. Normative References

 [1]  Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei, "Advanced
      Sockets Application Program Interface (API) for IPv6", RFC 3542,
      May 2003.
 [2]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
      IPv6", RFC 3775, June 2004.

12.2. Informative References

 [3]  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
      Specification", RFC 2460, December 1998.
 [4]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
      "Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
      January 2005.
 [5]  Nordmark, E., "IPv6 Socket API for source address selection",
      Work in Progress, July 2005.
 [6]  Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
      Stevens, "Basic Socket Interface Extensions for IPv6", RFC 3493,
      February 2003.

Authors' Addresses

 Samita Chakrabarti
 EMail: samitac2@gmail.com
 Erik Nordmark
 Sun Microsystems
 17 Network Circle
 Menlo Park, CA 94025
 USA
 Phone: +1 650 786 2921
 EMail: erik.nordmark@sun.com

Chakrabarti & Nordmark Informational [Page 24] RFC 4584 Sockets for API for Mobile IPv6 July 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
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 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
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 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Acknowledgement

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Chakrabarti & Nordmark Informational [Page 25]

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