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.

   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

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.

   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.

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.

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 */
      };

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 */
      };

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  */

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 */
      };

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 */

      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 */

      #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 */
      };

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]

      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;
      };

   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):

      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

   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.

   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.

   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.

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:

      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

   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].

   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.

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

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