INTERNET-DRAFT W. Richard Stevens Expires: May 21, 2002 Matt Thomas (Consultant) Obsoletes RFC 2292 Erik Nordmark (Sun) Tatuya Jinmei (Toshiba) November 21, 2001 Advanced Sockets API for IPv6 <draft-ietf-ipngwg-rfc2292bis-03.txt> Abstract A separate specification [RFC-2553] contain changes to the sockets API to support IP version 6. Those changes are for TCP and UDP-based applications and will support most end-user applications in use today: Telnet and FTP clients and servers, HTTP clients and servers, and the like. But another class of applications exists that will also be run under IPv6. We call these "advanced" applications and today this includes programs such as Ping, Traceroute, routing daemons, multicast routing daemons, router discovery daemons, and the like. The API feature typically used by these programs that make them "advanced" is a raw socket to access ICMPv4, IGMPv4, or IPv4, along with some knowledge of the packet header formats used by these protocols. To provide portability for applications that use raw sockets under IPv6, some standardization is needed for the advanced API features. There are other features of IPv6 that some applications will need to access: interface identification (specifying the outgoing interface and determining the incoming interface) and IPv6 extension headers that are not addressed in [RFC-2553]: The Routing header (source routing), Hop-by-Hop options, and Destination options. This document provides API access to these features too. Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months draft-ietf-ipngwg-rfc2292bis-03.txt [Page 1]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet Draft expires May 21, 2002. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 2]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 Table of Contents 1. Introduction ..................................................... 6 2. Common Structures and Definitions ................................ 7 2.1. The ip6_hdr Structure .......................................... 8 2.1.1. IPv6 Next Header Values ...................................... 8 2.1.2. IPv6 Extension Headers ....................................... 9 2.1.3. IPv6 Options ................................................. 10 2.2. The icmp6_hdr Structure ........................................ 11 2.2.1. ICMPv6 Type and Code Values .................................. 12 2.2.2. ICMPv6 Neighbor Discovery Definitions ........................ 13 2.2.3. Multicast Listener Discovery Definitions ..................... 15 2.2.4. ICMPv6 Router Renumbering Definitions ........................ 16 2.3. Address Testing Macros ......................................... 18 2.4. Protocols File ................................................. 18 3. IPv6 Raw Sockets ................................................. 19 3.1. Checksums ...................................................... 20 3.2. ICMPv6 Type Filtering .......................................... 21 3.3. ICMPv6 Verification of Received Packets ........................ 23 4. Access to IPv6 and Extension Headers ............................. 23 4.1. TCP Implications ............................................... 26 4.2. UDP and Raw Socket Implications ................................ 27 5. Extensions to Socket Ancillary Data .............................. 28 6. Packet Information ............................................... 28 6.1. Specifying/Receiving the Interface ............................. 29 6.2. Specifying/Receiving Source/Destination Address ................ 30 6.3. Specifying/Receiving the Hop Limit ............................. 31 6.4. Specifying the Next Hop Address ................................ 32 6.5. Specifying/Receiving the Traffic Class value ................... 32 6.6. Additional Errors with sendmsg() and setsockopt() .............. 33 6.7. Summary of outgoing interface selection ........................ 34 7. Routing Header Option ............................................ 34 7.1. inet6_rth_space ................................................ 36 7.2. inet6_rth_init ................................................. 36 7.3. inet6_rth_add .................................................. 37 7.4. inet6_rth_reverse .............................................. 37 7.5. inet6_rth_segments ............................................. 37 7.6. inet6_rth_getaddr .............................................. 38 8. Hop-By-Hop Options ............................................... 38 8.1. Receiving Hop-by-Hop Options ................................... 39 8.2. Sending Hop-by-Hop Options ..................................... 40 draft-ietf-ipngwg-rfc2292bis-03.txt [Page 3]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 9. Destination Options .............................................. 40 9.1. Receiving Destination Options .................................. 40 9.2. Sending Destination Options .................................... 41 10. Hop-by-Hop and Destination Options Processing ................... 41 10.1. inet6_opt_init ................................................ 42 10.2. inet6_opt_append .............................................. 42 10.3. inet6_opt_finish .............................................. 43 10.4. inet6_opt_set_val ............................................. 43 10.5. inet6_opt_next ................................................ 44 10.6. inet6_opt_find ................................................ 44 10.7. inet6_opt_get_val ............................................. 45 11. Additional Advanced API Functions ............................... 45 11.1. Sending with the Minimum MTU .................................. 45 11.2. Sending without fragmentation ................................. 46 11.3. Path MTU Discovery and UDP .................................... 46 11.4. Determining the current path MTU .............................. 47 11.5. Neighbor Reachability and UDP ................................. 48 12. Ordering of Ancillary Data and IPv6 Extension Headers ........... 49 13. IPv6-Specific Options with IPv4-Mapped IPv6 Addresses ........... 51 14. Extended interfaces for rresvport, rcmd and rexec ............... 51 14.1. rresvport_af .................................................. 51 14.2. rcmd_af ....................................................... 52 14.3. rexec_af ...................................................... 52 15. Summary of New Definitions ...................................... 52 16. Security Considerations ......................................... 56 17. Change History .................................................. 57 18. Open Issues ..................................................... 61 19. References ...................................................... 61 20. Acknowledgments ................................................. 61 21. Authors' Addresses .............................................. 62 22. Appendix A: Ancillary Data Overview ............................. 63 22.1. The msghdr Structure .......................................... 63 22.2. The cmsghdr Structure ......................................... 64 22.3. Ancillary Data Object Macros .................................. 65 22.3.1. CMSG_FIRSTHDR ............................................... 66 draft-ietf-ipngwg-rfc2292bis-03.txt [Page 4]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 22.3.2. CMSG_NXTHDR ................................................. 67 22.3.3. CMSG_DATA ................................................... 68 22.3.4. CMSG_SPACE .................................................. 68 22.3.5. CMSG_LEN .................................................... 69 23. Appendix B: Examples using the inet6_rth_XXX() functions ........ 69 23.1. Sending a Routing Header ...................................... 69 23.2. Receiving Routing Headers ..................................... 74 24. Appendix C: Examples using the inet6_opt_XXX() functions ........ 76 24.1. Building options .............................................. 76 24.2. Parsing received options ...................................... 78 draft-ietf-ipngwg-rfc2292bis-03.txt [Page 5]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 1. Introduction A separate specification [RFC-2553] contain changes to the sockets API to support IP version 6. Those changes are for TCP and UDP-based applications. This document defines some of the "advanced" features of the sockets API that are required for applications to take advantage of additional features of IPv6. Today, the portability of applications using IPv4 raw sockets is quite high, but this is mainly because most IPv4 implementations started from a common base (the Berkeley source code) or at least started with the Berkeley header files. This allows programs such as Ping and Traceroute, for example, to compile with minimal effort on many hosts that support the sockets API. With IPv6, however, there is no common source code base that implementors are starting from, and the possibility for divergence at this level between different implementations is high. To avoid a complete lack of portability amongst applications that use raw IPv6 sockets, some standardization is necessary. There are also features from the basic IPv6 specification that are not addressed in [RFC-2553]: sending and receiving Routing headers, Hop-by-Hop options, and Destination options, specifying the outgoing interface, and being told of the receiving interface. This document can be divided into the following main sections. 1. Definitions of the basic constants and structures required for applications to use raw IPv6 sockets. This includes structure definitions for the IPv6 and ICMPv6 headers and all associated constants (e.g., values for the Next Header field). 2. Some basic semantic definitions for IPv6 raw sockets. For example, a raw ICMPv4 socket requires the application to calculate and store the ICMPv4 header checksum. But with IPv6 this would require the application to choose the source IPv6 address because the source address is part of the pseudo header that ICMPv6 now uses for its checksum computation. It should be defined that with a raw ICMPv6 socket the kernel always calculates and stores the ICMPv6 header checksum. 3. Packet information: how applications can obtain the received interface, destination address, and received hop limit, along with specifying these values on a per-packet basis. There are a class of applications that need this capability and the technique should be portable. 4. Access to the optional Routing header, Hop-by-Hop options, and draft-ietf-ipngwg-rfc2292bis-03.txt [Page 6]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 Destination options extension headers. 5. Additional features required for improved IPv6 application portability. The packet information along with access to the extension headers (Routing header, Hop-by-Hop options, 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 does not address application access to either the authentication header or the encapsulating security payload header. All examples in this document omit error checking in favor of brevity and clarity. We note that many of the functions and socket options defined in this document may have error returns that are not defined in this document. Many of these possible error returns will be recognized only as implementations proceed. Datatypes 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). Note that we use the (unofficial) terminology ICMPv4, IGMPv4, and ARPv4 to avoid any confusion with the newer ICMPv6 protocol. 2. Common Structures and Definitions Many advanced applications examine fields in the IPv6 header and set and examine fields in the various ICMPv6 headers. Common structure definitions for these protocol headers are required, along with common constant definitions for the structure members. This API assumes that the fields in the protocol headers are left in the network byte order, which is big-endian for the Internet protocols. If not, then either these constants or the fields being tested must be converted at run-time, using something like htons() or htonl(). Two new header files are defined: <netinet/ip6.h> and <netinet/icmp6.h>. When an include file is specified, that include file is allowed to draft-ietf-ipngwg-rfc2292bis-03.txt [Page 7]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 include other files that do the actual declaration or definition. 2.1. The ip6_hdr Structure The following structure is defined as a result of including <netinet/ip6.h>. Note that this is a new header. struct ip6_hdr { union { struct ip6_hdrctl { uint32_t ip6_un1_flow; /* 4 bits version, 8 bits TC, 20 bits flow-ID */ uint16_t ip6_un1_plen; /* payload length */ uint8_t ip6_un1_nxt; /* next header */ uint8_t ip6_un1_hlim; /* hop limit */ } ip6_un1; uint8_t ip6_un2_vfc; /* 4 bits version, top 4 bits tclass */ } ip6_ctlun; struct in6_addr ip6_src; /* source address */ struct in6_addr ip6_dst; /* destination address */ }; #define ip6_vfc ip6_ctlun.ip6_un2_vfc #define ip6_flow ip6_ctlun.ip6_un1.ip6_un1_flow #define ip6_plen ip6_ctlun.ip6_un1.ip6_un1_plen #define ip6_nxt ip6_ctlun.ip6_un1.ip6_un1_nxt #define ip6_hlim ip6_ctlun.ip6_un1.ip6_un1_hlim #define ip6_hops ip6_ctlun.ip6_un1.ip6_un1_hlim 2.1.1. IPv6 Next Header Values IPv6 defines many new values for the Next Header field. The following constants are defined as a result of including <netinet/in.h>. #define IPPROTO_HOPOPTS 0 /* IPv6 Hop-by-Hop options */ #define IPPROTO_IPV6 41 /* IPv6 header */ #define IPPROTO_ROUTING 43 /* IPv6 Routing header */ #define IPPROTO_FRAGMENT 44 /* IPv6 fragmentation header */ #define IPPROTO_ESP 50 /* encapsulating security payload */ #define IPPROTO_AH 51 /* authentication header */ #define IPPROTO_ICMPV6 58 /* ICMPv6 */ #define IPPROTO_NONE 59 /* IPv6 no next header */ #define IPPROTO_DSTOPTS 60 /* IPv6 Destination options */ Berkeley-derived IPv4 implementations also define IPPROTO_IP to be 0. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 8]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 This should not be a problem since IPPROTO_IP is used only with IPv4 sockets and IPPROTO_HOPOPTS only with IPv6 sockets. 2.1.2. IPv6 Extension Headers Six extension headers are defined for IPv6. We define structures for all except the Authentication header and Encapsulating Security Payload header, both of which are beyond the scope of this document. The following structures are defined as a result of including <netinet/ip6.h>. /* Hop-by-Hop options header */ struct ip6_hbh { uint8_t ip6h_nxt; /* next header */ uint8_t ip6h_len; /* length in units of 8 octets */ /* followed by options */ }; /* Destination options header */ struct ip6_dest { uint8_t ip6d_nxt; /* next header */ uint8_t ip6d_len; /* length in units of 8 octets */ /* followed by options */ }; /* Routing header */ struct ip6_rthdr { uint8_t ip6r_nxt; /* next header */ uint8_t ip6r_len; /* length in units of 8 octets */ uint8_t ip6r_type; /* routing type */ uint8_t ip6r_segleft; /* segments left */ /* followed by routing type specific data */ }; /* Type 0 Routing header */ struct ip6_rthdr0 { uint8_t ip6r0_nxt; /* next header */ uint8_t ip6r0_len; /* length in units of 8 octets */ uint8_t ip6r0_type; /* always zero */ uint8_t ip6r0_segleft; /* segments left */ uint32_t ip6r0_reserved; /* reserved field */ /* followed by up to 127 struct in6_addr */ }; /* Fragment header */ struct ip6_frag { uint8_t ip6f_nxt; /* next header */ draft-ietf-ipngwg-rfc2292bis-03.txt [Page 9]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 uint8_t ip6f_reserved; /* reserved field */ uint16_t ip6f_offlg; /* offset, reserved, and flag */ uint32_t ip6f_ident; /* identification */ }; #if BYTE_ORDER == BIG_ENDIAN #define IP6F_OFF_MASK 0xfff8 /* mask out offset from _offlg */ #define IP6F_RESERVED_MASK 0x0006 /* reserved bits in ip6f_offlg */ #define IP6F_MORE_FRAG 0x0001 /* more-fragments flag */ #else /* BYTE_ORDER == LITTLE_ENDIAN */ #define IP6F_OFF_MASK 0xf8ff /* mask out offset from _offlg */ #define IP6F_RESERVED_MASK 0x0600 /* reserved bits in ip6f_offlg */ #define IP6F_MORE_FRAG 0x0100 /* more-fragments flag */ #endif 2.1.3. IPv6 Options Several options are defined for IPv6, and we define structures and macro definitions for some of them below. The following structures are defined as a result of including <netinet/ip6.h>. /* IPv6 options */ struct ip6_opt { uint8_t ip6o_type; uint8_t ip6o_len; }; /* * The high-order 3 bits of the option type define the behavior * when processing an unknown option and whether or not the option * content changes in flight. */ #define IP6OPT_TYPE(o) ((o) & 0xc0) #define IP6OPT_TYPE_SKIP 0x00 #define IP6OPT_TYPE_DISCARD 0x40 #define IP6OPT_TYPE_FORCEICMP 0x80 #define IP6OPT_TYPE_ICMP 0xc0 #define IP6OPT_MUTABLE 0x20 #define IP6OPT_PAD1 0x00 /* 00 0 00000 */ #define IP6OPT_PADN 0x01 /* 00 0 00001 */ #define IP6OPT_JUMBO 0xc2 /* 11 0 00010 */ #define IP6OPT_NSAP_ADDR 0xc3 /* 11 0 00011 */ #define IP6OPT_TUNNEL_LIMIT 0x04 /* 00 0 00100 */ #define IP6OPT_ROUTER_ALERT 0x05 /* 00 0 00101 */ draft-ietf-ipngwg-rfc2292bis-03.txt [Page 10]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 /* Jumbo Payload Option */ struct ip6_opt_jumbo { uint8_t ip6oj_type; uint8_t ip6oj_len; uint8_t ip6oj_jumbo_len[4]; }; #define IP6OPT_JUMBO_LEN 6 /* NSAP Address Option */ struct ip6_opt_nsap { uint8_t ip6on_type; uint8_t ip6on_len; uint8_t ip6on_src_nsap_len; uint8_t ip6on_dst_nsap_len; /* followed by source NSAP */ /* followed by destination NSAP */ }; /* Tunnel Limit Option */ struct ip6_opt_tunnel { uint8_t ip6ot_type; uint8_t ip6ot_len; uint8_t ip6ot_encap_limit; }; /* Router Alert Option */ struct ip6_opt_router { uint8_t ip6or_type; uint8_t ip6or_len; uint8_t ip6or_value[2]; }; /* Router alert values (in network byte order) */ #ifdef _BIG_ENDIAN #define IP6_ALERT_MLD 0x0000 #define IP6_ALERT_RSVP 0x0001 #define IP6_ALERT_AN 0x0002 #else #define IP6_ALERT_MLD 0x0000 #define IP6_ALERT_RSVP 0x0100 #define IP6_ALERT_AN 0x0200 #endif 2.2. The icmp6_hdr Structure The ICMPv6 header is needed by numerous IPv6 applications including draft-ietf-ipngwg-rfc2292bis-03.txt [Page 11]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 Ping, Traceroute, router discovery daemons, and neighbor discovery daemons. The following structure is defined as a result of including <netinet/icmp6.h>. Note that this is a new header. struct icmp6_hdr { uint8_t icmp6_type; /* type field */ uint8_t icmp6_code; /* code field */ uint16_t icmp6_cksum; /* checksum field */ union { uint32_t icmp6_un_data32[1]; /* type-specific field */ uint16_t icmp6_un_data16[2]; /* type-specific field */ uint8_t icmp6_un_data8[4]; /* type-specific field */ } icmp6_dataun; }; #define icmp6_data32 icmp6_dataun.icmp6_un_data32 #define icmp6_data16 icmp6_dataun.icmp6_un_data16 #define icmp6_data8 icmp6_dataun.icmp6_un_data8 #define icmp6_pptr icmp6_data32[0] /* parameter prob */ #define icmp6_mtu icmp6_data32[0] /* packet too big */ #define icmp6_id icmp6_data16[0] /* echo request/reply */ #define icmp6_seq icmp6_data16[1] /* echo request/reply */ #define icmp6_maxdelay icmp6_data16[0] /* mcast group membership */ 2.2.1. ICMPv6 Type and Code Values In addition to a common structure for the ICMPv6 header, common definitions are required for the ICMPv6 type and code fields. The following constants are also defined as a result of including <netinet/icmp6.h>. #define ICMP6_DST_UNREACH 1 #define ICMP6_PACKET_TOO_BIG 2 #define ICMP6_TIME_EXCEEDED 3 #define ICMP6_PARAM_PROB 4 #define ICMP6_INFOMSG_MASK 0x80 /* all informational messages */ #define ICMP6_ECHO_REQUEST 128 #define ICMP6_ECHO_REPLY 129 #define ICMP6_DST_UNREACH_NOROUTE 0 /* no route to destination */ #define ICMP6_DST_UNREACH_ADMIN 1 /* communication with */ /* destination */ /* admin. prohibited */ #define ICMP6_DST_UNREACH_BEYONDSCOPE 2 /* beyond scope of source address */ draft-ietf-ipngwg-rfc2292bis-03.txt [Page 12]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 #define ICMP6_DST_UNREACH_ADDR 3 /* address unreachable */ #define ICMP6_DST_UNREACH_NOPORT 4 /* bad port */ #define ICMP6_TIME_EXCEED_TRANSIT 0 /* Hop Limit == 0 in transit */ #define ICMP6_TIME_EXCEED_REASSEMBLY 1 /* Reassembly time out */ #define ICMP6_PARAMPROB_HEADER 0 /* erroneous header field */ #define ICMP6_PARAMPROB_NEXTHEADER 1 /* unrecognized Next Header */ #define ICMP6_PARAMPROB_OPTION 2 /* unrecognized IPv6 option */ The five ICMP message types defined by IPv6 neighbor discovery (133- 137) are defined in the next section. 2.2.2. ICMPv6 Neighbor Discovery Definitions The following structures and definitions are defined as a result of including <netinet/icmp6.h>. #define ND_ROUTER_SOLICIT 133 #define ND_ROUTER_ADVERT 134 #define ND_NEIGHBOR_SOLICIT 135 #define ND_NEIGHBOR_ADVERT 136 #define ND_REDIRECT 137 struct nd_router_solicit { /* router solicitation */ struct icmp6_hdr nd_rs_hdr; /* could be followed by options */ }; #define nd_rs_type nd_rs_hdr.icmp6_type #define nd_rs_code nd_rs_hdr.icmp6_code #define nd_rs_cksum nd_rs_hdr.icmp6_cksum #define nd_rs_reserved nd_rs_hdr.icmp6_data32[0] struct nd_router_advert { /* router advertisement */ struct icmp6_hdr nd_ra_hdr; uint32_t nd_ra_reachable; /* reachable time */ uint32_t nd_ra_retransmit; /* retransmit timer */ /* could be followed by options */ }; #define nd_ra_type nd_ra_hdr.icmp6_type #define nd_ra_code nd_ra_hdr.icmp6_code #define nd_ra_cksum nd_ra_hdr.icmp6_cksum #define nd_ra_curhoplimit nd_ra_hdr.icmp6_data8[0] #define nd_ra_flags_reserved nd_ra_hdr.icmp6_data8[1] #define ND_RA_FLAG_MANAGED 0x80 draft-ietf-ipngwg-rfc2292bis-03.txt [Page 13]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 #define ND_RA_FLAG_OTHER 0x40 #define nd_ra_router_lifetime nd_ra_hdr.icmp6_data16[1] struct nd_neighbor_solicit { /* neighbor solicitation */ struct icmp6_hdr nd_ns_hdr; struct in6_addr nd_ns_target; /* target address */ /* could be followed by options */ }; #define nd_ns_type nd_ns_hdr.icmp6_type #define nd_ns_code nd_ns_hdr.icmp6_code #define nd_ns_cksum nd_ns_hdr.icmp6_cksum #define nd_ns_reserved nd_ns_hdr.icmp6_data32[0] struct nd_neighbor_advert { /* neighbor advertisement */ struct icmp6_hdr nd_na_hdr; struct in6_addr nd_na_target; /* target address */ /* could be followed by options */ }; #define nd_na_type nd_na_hdr.icmp6_type #define nd_na_code nd_na_hdr.icmp6_code #define nd_na_cksum nd_na_hdr.icmp6_cksum #define nd_na_flags_reserved nd_na_hdr.icmp6_data32[0] #if BYTE_ORDER == BIG_ENDIAN #define ND_NA_FLAG_ROUTER 0x80000000 #define ND_NA_FLAG_SOLICITED 0x40000000 #define ND_NA_FLAG_OVERRIDE 0x20000000 #else /* BYTE_ORDER == LITTLE_ENDIAN */ #define ND_NA_FLAG_ROUTER 0x00000080 #define ND_NA_FLAG_SOLICITED 0x00000040 #define ND_NA_FLAG_OVERRIDE 0x00000020 #endif struct nd_redirect { /* redirect */ struct icmp6_hdr nd_rd_hdr; struct in6_addr nd_rd_target; /* target address */ struct in6_addr nd_rd_dst; /* destination address */ /* could be followed by options */ }; #define nd_rd_type nd_rd_hdr.icmp6_type #define nd_rd_code nd_rd_hdr.icmp6_code #define nd_rd_cksum nd_rd_hdr.icmp6_cksum #define nd_rd_reserved nd_rd_hdr.icmp6_data32[0] struct nd_opt_hdr { /* Neighbor discovery option header */ uint8_t nd_opt_type; draft-ietf-ipngwg-rfc2292bis-03.txt [Page 14]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 uint8_t nd_opt_len; /* in units of 8 octets */ /* followed by option specific data */ }; #define ND_OPT_SOURCE_LINKADDR 1 #define ND_OPT_TARGET_LINKADDR 2 #define ND_OPT_PREFIX_INFORMATION 3 #define ND_OPT_REDIRECTED_HEADER 4 #define ND_OPT_MTU 5 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; }; #define ND_OPT_PI_FLAG_ONLINK 0x80 #define ND_OPT_PI_FLAG_AUTO 0x40 struct nd_opt_rd_hdr { /* redirected header */ uint8_t nd_opt_rh_type; uint8_t nd_opt_rh_len; uint16_t nd_opt_rh_reserved1; uint32_t nd_opt_rh_reserved2; /* followed by IP header and data */ }; struct nd_opt_mtu { /* MTU option */ uint8_t nd_opt_mtu_type; uint8_t nd_opt_mtu_len; uint16_t nd_opt_mtu_reserved; uint32_t nd_opt_mtu_mtu; }; We note that the nd_na_flags_reserved flags have the same byte ordering problems as we discussed with ip6f_offlg. 2.2.3. Multicast Listener Discovery Definitions The following structures and definitions are defined as a result of including <netinet/icmp6.h>. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 15]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 #define MLD_LISTENER_QUERY 130 #define MLD_LISTENER_REPORT 131 #define MLD_LISTENER_REDUCTION 132 struct mld_hdr { struct icmp6_hdr mld_hdr; struct in6_addr mld_addr; /* multicast address */ }; #define mld_type mld_hdr.icmp6_type #define mld_code mld_hdr.icmp6_code #define mld_cksum mld_hdr.icmp6_cksum #define mld_maxdelay mld_hdr.icmp6_data16[0] #define mld_reserved mld_hdr.icmp6_data16[1] 2.2.4. ICMPv6 Router Renumbering Definitions The following structures and definitions are defined as a result of including <netinet/icmp6.h>. #define ICMP6_ROUTER_RENUMBERING 138 /* router renumbering */ struct icmp6_router_renum { /* router renumbering header */ struct icmp6_hdr rr_hdr; uint8_t rr_segnum; uint8_t rr_flags; uint16_t rr_maxdelay; uint32_t rr_reserved; }; #define rr_type rr_hdr.icmp6_type #define rr_code rr_hdr.icmp6_code #define rr_cksum rr_hdr.icmp6_cksum #define rr_seqnum rr_hdr.icmp6_data32[0] /* Router renumbering flags */ #define ICMP6_RR_FLAGS_TEST 0x80 #define ICMP6_RR_FLAGS_REQRESULT 0x40 #define ICMP6_RR_FLAGS_FORCEAPPLY 0x20 #define ICMP6_RR_FLAGS_SPECSITE 0x10 #define ICMP6_RR_FLAGS_PREVDONE 0x08 struct rr_pco_match { /* match prefix part */ uint8_t rpm_code; uint8_t rpm_len; uint8_t rpm_ordinal; uint8_t rpm_matchlen; draft-ietf-ipngwg-rfc2292bis-03.txt [Page 16]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 uint8_t rpm_minlen; uint8_t rpm_maxlen; uint16_t rpm_reserved; struct in6_addr rpm_prefix; }; /* PCO code values */ #define RPM_PCO_ADD 1 #define RPM_PCO_CHANGE 2 #define RPM_PCO_SETGLOBAL 3 struct rr_pco_use { /* use prefix part */ uint8_t rpu_uselen; uint8_t rpu_keeplen; uint8_t rpu_ramask; uint8_t rpu_raflags; uint32_t rpu_vltime; uint32_t rpu_pltime; uint32_t rpu_flags; struct in6_addr rpu_prefix; }; #define ICMP6_RR_PCOUSE_RAFLAGS_ONLINK 0x20 #define ICMP6_RR_PCOUSE_RAFLAGS_AUTO 0x10 #if BYTE_ORDER == BIG_ENDIAN #define ICMP6_RR_PCOUSE_FLAGS_DECRVLTIME 0x80000000 #define ICMP6_RR_PCOUSE_FLAGS_DECRPLTIME 0x40000000 #elif BYTE_ORDER == LITTLE_ENDIAN #define ICMP6_RR_PCOUSE_FLAGS_DECRVLTIME 0x80 #define ICMP6_RR_PCOUSE_FLAGS_DECRPLTIME 0x40 #endif struct rr_result { /* router renumbering result message */ uint16_t rrr_flags; uint8_t rrr_ordinal; uint8_t rrr_matchedlen; uint32_t rrr_ifid; struct in6_addr rrr_prefix; }; #if BYTE_ORDER == BIG_ENDIAN #define ICMP6_RR_RESULT_FLAGS_OOB 0x0002 #define ICMP6_RR_RESULT_FLAGS_FORBIDDEN 0x0001 #elif BYTE_ORDER == LITTLE_ENDIAN #define ICMP6_RR_RESULT_FLAGS_OOB 0x0200 #define ICMP6_RR_RESULT_FLAGS_FORBIDDEN 0x0100 #endif draft-ietf-ipngwg-rfc2292bis-03.txt [Page 17]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 2.3. Address Testing Macros The basic API ([RFC-2553]) defines some macros for testing an IPv6 address for certain properties. This API extends those definitions with additional address testing macros, defined as a result of including <netinet/in.h>. int IN6_ARE_ADDR_EQUAL(const struct in6_addr *, const struct in6_addr *); This macro returns non-zero if the addresses are equal; otherwise it returns zero. 2.4. Protocols File Many hosts provide the file /etc/protocols that contains the names of the various IP protocols and their protocol number (e.g., the value of the protocol field in the IPv4 header for that protocol, such as 1 for ICMP). Some programs then call the function getprotobyname() to obtain the protocol value that is then specified as the third argument to the socket() function. For example, the Ping program contains code of the form struct protoent *proto; proto = getprotobyname("icmp"); s = socket(PF_INET, SOCK_RAW, proto->p_proto); Common names are required for the new IPv6 protocols in this file, to provide portability of applications that call the getprotoXXX() functions. We define the following protocol names with the values shown. These are taken from http://www.iana.org/assignments/protocol-numbers. hopopt 0 # hop-by-hop options for ipv6 ipv6 41 # ipv6 ipv6-route 43 # routing header for ipv6 ipv6-frag 44 # fragment header for ipv6 esp 50 # encapsulating security payload for ipv6 ah 51 # authentication header for ipv6 ipv6-icmp 58 # icmp for ipv6 ipv6-nonxt 59 # no next header for ipv6 ipv6-opts 60 # destination options for ipv6 draft-ietf-ipngwg-rfc2292bis-03.txt [Page 18]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 3. IPv6 Raw Sockets Raw sockets bypass the transport layer (TCP or UDP). With IPv4, raw sockets are used to access ICMPv4, IGMPv4, and to read and write IPv4 datagrams containing a protocol field that the kernel does not process. An example of the latter is a routing daemon for OSPF, since it uses IPv4 protocol field 89. With IPv6 raw sockets will be used for ICMPv6 and to read and write IPv6 datagrams containing a Next Header field that the kernel does not process. Examples of the latter are a routing daemon for OSPF for IPv6 and RSVP (protocol field 46). All data sent via raw sockets MUST be in network byte order and all data received via raw sockets will be in network byte order. This differs from the IPv4 raw sockets, which did not specify a byte ordering and used the host's byte order for certain IP header fields. Another difference from IPv4 raw sockets is that complete packets (that is, IPv6 packets with extension headers) cannot be sent or received using the IPv6 raw sockets API. Instead, ancillary data objects are used to transfer the extension headers and hoplimit information, as described in Section 6. Should an application need access to the complete IPv6 packet, some other technique, such as the datalink interfaces BPF or DLPI, must be used. All fields except the flow label field in the IPv6 header that an application might want to change (i.e., everything other than the version number) can be modified using ancillary data and/or socket options by the application for output. All fields except the flow label field in a received IPv6 header (other than the version number and Next Header fields) and all extension headers that an application might want to specify are also made available to the application as ancillary data on input. Hence there is no need for a socket option similar to the IPv4 IP_HDRINCL socket option and on receipt the application will only receive the payload i.e. the data after the IPv6 header and all the extension headers. This API does not define access to the flow label field, because today there is no standard usage of the field. When writing to a raw socket the kernel will automatically fragment the packet if its size exceeds the path MTU, inserting the required fragmentation headers. On input the kernel reassembles received fragments, so the reader of a raw socket never sees any fragment headers. When we say "an ICMPv6 raw socket" we mean a socket created by calling the socket function with the three arguments PF_INET6, draft-ietf-ipngwg-rfc2292bis-03.txt [Page 19]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 SOCK_RAW, and IPPROTO_ICMPV6. Most IPv4 implementations give special treatment to a raw socket created with a third argument to socket() of IPPROTO_RAW, whose value is normally 255, to have it mean that the application will send down complete packets including the IPv4 header. (Note: This feature was added to IPv4 in 1988 by Van Jacobson to support traceroute, allowing a complete IP header to be passed by the application, before the IP_HDRINCL socket option was added.) We note that IPPROTO_RAW has no special meaning to an IPv6 raw socket (and the IANA currently reserves the value of 255 when used as a next-header field). 3.1. Checksums The kernel will calculate and insert the ICMPv6 checksum for ICMPv6 raw sockets, since this checksum is mandatory. For other raw IPv6 sockets (that is, for raw IPv6 sockets created with a third argument other than IPPROTO_ICMPV6), the application must set the new IPV6_CHECKSUM socket option to have the kernel (1) compute and store a checksum for output, and (2) verify the received checksum on input, discarding the packet if the checksum is in error. This option prevents applications from having to perform source address selection on the packets they send. The checksum will incorporate the IPv6 pseudo-header, defined in Section 8.1 of [RFC- 2460]. This new socket option also specifies an integer offset into the user data of where the checksum is located. int offset = 2; setsockopt(fd, IPPROTO_IPV6, IPV6_CHECKSUM, &offset, sizeof(offset)); By default, this socket option is disabled. Setting the offset to -1 also disables the option. By disabled we mean (1) the kernel will not calculate and store a checksum for outgoing packets, and (2) the kernel will not verify a checksum for received packets. This option assumes the use of the 16-bit one's complement of the one's complement sum as the checksum algorithm and that the checksum field is aligned on a 16-bit boundary. Thus, specifying a positive odd value as offset is invalid, and setsockopt() will fail for odd offset values. An attempt to set IPV6_CHECKSUM for an ICMPv6 socket will fail. (Note: Since the checksum is always calculated by the kernel for an ICMPv6 socket, applications are not able to generate ICMPv6 packets with incorrect checksums (presumably for testing purposes) using this draft-ietf-ipngwg-rfc2292bis-03.txt [Page 20]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 API.) 3.2. ICMPv6 Type Filtering ICMPv4 raw sockets receive most ICMPv4 messages received by the kernel. (We say "most" and not "all" because Berkeley-derived kernels never pass echo requests, timestamp requests, or address mask requests to a raw socket. Instead these three messages are processed entirely by the kernel.) But ICMPv6 is a superset of ICMPv4, also including the functionality of IGMPv4 and ARPv4. This means that an ICMPv6 raw socket can potentially receive many more messages than would be received with an ICMPv4 raw socket: ICMP messages similar to ICMPv4, along with neighbor solicitations, neighbor advertisements, and the three multicast listener discovery messages. Most applications using an ICMPv6 raw socket care about only a small subset of the ICMPv6 message types. To transfer extraneous ICMPv6 messages from the kernel to user can incur a significant overhead. Therefore this API includes a method of filtering ICMPv6 messages by the ICMPv6 type field. Each ICMPv6 raw socket has an associated filter whose datatype is defined as struct icmp6_filter; This structure, along with the macros and constants defined later in this section, are defined as a result of including the <netinet/icmp6.h>. The current filter is fetched and stored using getsockopt() and setsockopt() with a level of IPPROTO_ICMPV6 and an option name of ICMP6_FILTER. Six macros operate on an icmp6_filter structure: void ICMP6_FILTER_SETPASSALL (struct icmp6_filter *); void ICMP6_FILTER_SETBLOCKALL(struct icmp6_filter *); void ICMP6_FILTER_SETPASS ( int, struct icmp6_filter *); void ICMP6_FILTER_SETBLOCK( int, struct icmp6_filter *); int ICMP6_FILTER_WILLPASS (int, const struct icmp6_filter *); int ICMP6_FILTER_WILLBLOCK(int, const struct icmp6_filter *); draft-ietf-ipngwg-rfc2292bis-03.txt [Page 21]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 The first argument to the last four macros (an integer) is an ICMPv6 message type, between 0 and 255. The pointer argument to all six macros is a pointer to a filter that is modified by the first four macros examined by the last two macros. The first two macros, SETPASSALL and SETBLOCKALL, let us specify that all ICMPv6 messages are passed to the application or that all ICMPv6 messages are blocked from being passed to the application. The next two macros, SETPASS and SETBLOCK, let us specify that messages of a given ICMPv6 type should be passed to the application or not passed to the application (blocked). The final two macros, WILLPASS and WILLBLOCK, return true or false depending whether the specified message type is passed to the application or blocked from being passed to the application by the filter pointed to by the second argument. When an ICMPv6 raw socket is created, it will by default pass all ICMPv6 message types to the application. As an example, a program that wants to receive only router advertisements could execute the following: struct icmp6_filter myfilt; fd = socket(PF_INET6, SOCK_RAW, IPPROTO_ICMPV6); ICMP6_FILTER_SETBLOCKALL(&myfilt); ICMP6_FILTER_SETPASS(ND_ROUTER_ADVERT, &myfilt); setsockopt(fd, IPPROTO_ICMPV6, ICMP6_FILTER, &myfilt, sizeof(myfilt)); The filter structure is declared and then initialized to block all messages types. The filter structure is then changed to allow router advertisement messages to be passed to the application and the filter is installed using setsockopt(). In order to clear an installed filter the application can issue a setsockopt for ICMP6_FILTER with a zero length. When no such filter has been installed corresponding getsockopt() will return the kernel default filter. The icmp6_filter structure is similar to the fd_set datatype used with the select() function in the sockets API. The icmp6_filter structure is an opaque datatype and the application should not care how it is implemented. All the application does with this datatype is allocate a variable of this type, pass a pointer to a variable of this type to getsockopt() and setsockopt(), and operate on a variable draft-ietf-ipngwg-rfc2292bis-03.txt [Page 22]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 of this type using the six macros that we just defined. Nevertheless, it is worth showing a simple implementation of this datatype and the six macros. struct icmp6_filter { uint32_t icmp6_filt[8]; /* 8*32 = 256 bits */ }; #define ICMP6_FILTER_WILLPASS(type, filterp) \ ((((filterp)->icmp6_filt[(type) >> 5]) & (1 << ((type) & 31))) != 0) #define ICMP6_FILTER_WILLBLOCK(type, filterp) \ ((((filterp)->icmp6_filt[(type) >> 5]) & (1 << ((type) & 31))) == 0) #define ICMP6_FILTER_SETPASS(type, filterp) \ ((((filterp)->icmp6_filt[(type) >> 5]) |= (1 << ((type) & 31)))) #define ICMP6_FILTER_SETBLOCK(type, filterp) \ ((((filterp)->icmp6_filt[(type) >> 5]) &= ~(1 << ((type) & 31)))) #define ICMP6_FILTER_SETPASSALL(filterp) \ memset((filterp), 0xFF, sizeof(struct icmp6_filter)) #define ICMP6_FILTER_SETBLOCKALL(filterp) \ memset((filterp), 0, sizeof(struct icmp6_filter)) (Note: These sample definitions have two limitations that an implementation may want to change. The first four macros evaluate their first argument two times. The second two macros require the inclusion of the <string.h> header for the memset() function.) 3.3. ICMPv6 Verification of Received Packets The protocol stack will verify the ICMPv6 checksum and discard any packets with invalid checksums. An implementation might perform additional validity checks on the ICMPv6 message content and discard malformed packets. However, a portable application must not assume that such validity checks have been performed. The protocol stack should not automatically discard packets if the ICMP type is unknown to the stack. For extensibility reasons received ICMP packets with any type (informational or error) must be passed to the applications (subject to ICMP6_FILTER filtering on the type value and the checksum verification). 4. Access to IPv6 and Extension Headers Applications need to be able to control IPv6 header and extension draft-ietf-ipngwg-rfc2292bis-03.txt [Page 23]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 header content when sending as well as being able to receive the content of these headers. This is done by defining socket option types which can be used both with setsockopt and with ancillary data. Ancillary data is discussed in Appendix A. The following optional information can be exchanged between the application and the kernel: 1. The send/receive interface and source/destination address, 2. The hop limit, 3. Next hop address, 4. The traffic class, 4. Routing header, 5. Hop-by-Hop options header, and 6. Destination options header (both before and after a Routing header). First, to receive any of this optional information (other than the next hop address, which can only be set), the application must call setsockopt() to turn on the corresponding flag: int on = 1; setsockopt(fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &on, sizeof(on)); setsockopt(fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &on, sizeof(on)); setsockopt(fd, IPPROTO_IPV6, IPV6_RECVRTHDR, &on, sizeof(on)); setsockopt(fd, IPPROTO_IPV6, IPV6_RECVHOPOPTS, &on, sizeof(on)); setsockopt(fd, IPPROTO_IPV6, IPV6_RECVDSTOPTS, &on, sizeof(on)); setsockopt(fd, IPPROTO_IPV6, IPV6_RECVTCLASS, &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. Two different mechanisms exist for sending this optional information: 1. Using setsockopt to specify the option content for a socket. These are known "sticky" options since they affect all transmitted packets on the socket until either a new setsockopt is done or the options are overridden using ancillary data. 2. Using ancillary data to specify the option content for a single datagram. This only applies to datagram and raw sockets; not to TCP sockets. The three socket option parameters and the three cmsghdr fields that describe the options/ancillary data objects are summarized as: draft-ietf-ipngwg-rfc2292bis-03.txt [Page 24]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 opt level/ optname/ optval/ cmsg_level cmsg_type cmsg_data[] ------------ ------------ ------------------------ IPPROTO_IPV6 IPV6_PKTINFO in6_pktinfo structure IPPROTO_IPV6 IPV6_HOPLIMIT int IPPROTO_IPV6 IPV6_NEXTHOP socket address structure IPPROTO_IPV6 IPV6_RTHDR ip6_rthdr structure IPPROTO_IPV6 IPV6_HOPOPTS ip6_hbh structure IPPROTO_IPV6 IPV6_DSTOPTS ip6_dest structure IPPROTO_IPV6 IPV6_RTHDRDSTOPTS ip6_dest structure IPPROTO_IPV6 IPV6_TCLASS int (Note: IPV6_HOPLIMIT can be used as ancillary data items only) All these options are described in detail in Section 6, 7, 8 and 9. All the constants beginning with IPV6_ are defined as a result of including the <netinet/in.h>. Note: We intentionally use the same constant for the cmsg_level member as is used as the second argument to getsockopt() and setsockopt() (what is called the "level"), and the same constant for the cmsg_type member as is used as the third argument to getsockopt() and setsockopt() (what is called the "option name"). Issuing getsockopt() for the above options will return the sticky option value i.e. the value set with setsockopt(). If no sticky option value has been set getsockopt() will return the following values: - For the IPV6_PKTINFO option, it will return an in6_pktinfo structure with ipi6_addr being in6addr_any and ipi6_ifindex being zero. - For the IPV6_TCLASS option, it will return the kernel default value. - For other options, it will indicate the lack of the option value with optlen being zero. The application does not explicitly need to access the data structures for the Routing header, Hop-by-Hop options header, and Destination options header, since the API to these features is through a set of inet6_rth_XXX() and inet6_opt_XXX() functions that we define in Section 7 and Section 10. Those functions simplify the interface to these features instead of requiring the application to draft-ietf-ipngwg-rfc2292bis-03.txt [Page 25]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 know the intimate details of the extension header formats. 4.1. TCP Implications It is not possible to use ancillary data to transmit the above options for TCP since there is not a one-to-one mapping between send operations and the TCP segments being transmitted. Instead an application can use setsockopt to specify them as sticky options. When the application uses setsockopt to specify the above options it is expected that TCP will start using the new information when sending segments. However, TCP may or may not use the new information when retransmitting segments that were originally sent when the old sticky options were in effect. Applications using TCP could use ancillary data to receive the IPv6 and extension header information by enabling the desired IPV6_RECVxxx options and using recvmsg(). However, this is not feasible due to the lack of mapping between received TCP segments and recv operations. Also, since most TCP applications do not use recvmsg(), this type of approach would introduce an additional cost to application programmers. This specification thus provides a different method for access to optional information by the IPV6_PKTOPTIONS socket option. getsockopt(fd, IPPROTO_IPV6, IPV6_PKTOPTIONS, buf, &len); returns a buffer with one or more ancillary data objects for all the optional receive information that the application has previously specified that it wants to receive. The fourth argument points to the buffer that is filled in by the call. The fifth argument is a pointer to a value-result integer: when the function is called the integer specifies the size of the buffer pointed to by the fourth argument, and on return this integer contains the actual number of bytes that were returned. The application processes this buffer exactly as if the buffer were returned by recvmsg() as control information. When a TCP application requires the kernel to pass optional information by IPV6_RECVxxx options, the kernel stores the corresponding information of the last-received segment. That is, the stored information will be overridden when the kernel receives a segment before the application calls getsockopt() for IPV6_PKTOPTIONS. This means that applications usually cannot follow all changes on the optional information. Thus, applications should not use the optional information for authentication or qualification purposes. The information can only be used as some hints about the received packets. For the same reason, it is not meaningful to poll draft-ietf-ipngwg-rfc2292bis-03.txt [Page 26]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 the socket periodically in order to see if there have been some changes on the received packets. The IPV6_PKTOPTIONS socket option is a get-only option, and can only be used by a TCP socket. 4.2. UDP and Raw Socket Implications The receive behavior for UDP and raw sockets is quite straightforward. After the application has enabled an IPV6_RECVxxx socket option it will receive ancillary data items for every recvmsg() call containing the requested information. However, if the information is not present in the packet the ancillary data item will not be included. For example, if the application enables IPV6_RECVRTHDR and a received datagram does not contain a Routing header there will not be an IPV6_RTHDR ancillary data item. Note that due to buffering in the socket implementation there might be some packets queued when an IPV6_RECVxxx option is enabled and they might not have the ancillary data information. For sending the application has the choice between using sticky options and ancillary data. The application can also use both having the sticky options specify the "default" and using ancillary data to override the default options. When an ancillary data item is specified in a call to sendmsg(), the item will override an existing sticky option of the same name (if previously specified). For example, if the application has set IPV6_RTHDR using a sticky option and later passes IPV6_RTHDR as ancillary data this will override the IPV6_RTHDR sticky option and the routing header of the outgoing packet will be from the ancillary data item, not from the sticky option. Note, however, that other sticky options than IPV6_RTHDR will not be affected by the IPV6_RTHDR ancillary data item; the overriding mechanism only works for the same type of sticky options and ancillary data items. (Note: the overriding rule is different from the one in RFC 2292. In RFC 2292, an ancillary data item overrode all sticky options previously defined. This was reasonable, because sticky options could only be specified as a set by a single socket option. However, in this API, each option is separated so that it can be specified as a single sticky option. Additionally, there are much more ancillary data items and sticky options than in RFC 2292, including ancillary- only one. Thus, it should be natural for application programmers to separate the overriding rule as well.) An application can also temporarily disable a particular sticky draft-ietf-ipngwg-rfc2292bis-03.txt [Page 27]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 option by specifying a corresponding ancillary data item that could disable the sticky option when being used as an argument for a socket option. For example, if the application has set IPV6_HOPOPTS as a sticky option and later passes IPV6_HOPOPTS with a zero length as an ancillary data item, the packet will not have a Hop-by-Hop options header. 5. Extensions to Socket Ancillary Data This specification uses ancillary data as defined in Posix.1g with the following compatible extensions: - CMSG_NXTHDR has been extended to handle a NULL 2nd argument to mean "get the first header". See Section 22.3.2. - A new CMSG_SPACE macro is defined. It is used to determine how much space need to be allocated for an ancillary data item. See Section 22.3.4. - A new CMSG_LEN macro is defined. It returns the value to store in the cmsg_len member of the cmsghdr structure, taking into account any padding needed to satisfy alignment requirements. See Section 22.3.5. 6. Packet Information There are five pieces of information that an application can specify for an outgoing packet using ancillary data: 1. the source IPv6 address, 2. the outgoing interface index, 3. the outgoing hop limit, 4. the next hop address, and 5. the outgoing traffic class value. Four similar pieces of information can be returned for a received packet as ancillary data: 1. the destination IPv6 address, 2. the arriving interface index, 3. the arriving hop limit, and 4. the arriving traffic class value. The first two pieces of information are contained in an in6_pktinfo structure that is set with setsockopt() or sent as ancillary data draft-ietf-ipngwg-rfc2292bis-03.txt [Page 28]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 with sendmsg() and received as ancillary data with recvmsg(). This structure is defined as a result of including the <netinet/in.h>. struct in6_pktinfo { struct in6_addr ipi6_addr; /* src/dst IPv6 address */ unsigned int ipi6_ifindex; /* send/recv interface index */ }; In the socket option and cmsghdr level will be IPPROTO_IPV6, the type will be IPV6_PKTINFO, and the first byte of the option value and cmsg_data[] will be the first byte of the in6_pktinfo structure. An application can clear any sticky IPV6_PKTINFO option by doing a "regular" setsockopt with ipi6_addr being in6addr_any and ipi6_ifindex being zero. This information is returned as ancillary data by recvmsg() only if the application has enabled the IPV6_RECVPKTINFO socket option: int on = 1; setsockopt(fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &on, sizeof(on)); (Note: The hop limit is not contained in the in6_pktinfo structure for the following reason. Some UDP servers want to respond to client requests by sending their reply out the same interface on which the request was received and with the source IPv6 address of the reply equal to the destination IPv6 address of the request. To do this the application can enable just the IPV6_RECVPKTINFO socket option and then use the received control information from recvmsg() as the outgoing control information for sendmsg(). The application need not examine or modify the in6_pktinfo structure at all. But if the hop limit were contained in this structure, the application would have to parse the received control information and change the hop limit member, since the received hop limit is not the desired value for an outgoing packet.) 6.1. Specifying/Receiving the Interface Interfaces on an IPv6 node are identified by a small positive integer, as described in Section 4 of [RFC-2553]. That document also describes a function to map an interface name to its interface index, a function to map an interface index to its interface name, and a function to return all the interface names and indexes. Notice from this document that no interface is ever assigned an index of 0. When specifying the outgoing interface, if the ipi6_ifindex value is 0, the kernel will choose the outgoing interface. If the application draft-ietf-ipngwg-rfc2292bis-03.txt [Page 29]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 specifies an outgoing interface for a multicast packet, the interface specified by the ancillary data overrides any interface specified by the IPV6_MULTICAST_IF socket option (described in [RFC-2553]), for that call to sendmsg() only. Also, if the application specifies an outgoing interface for a multicast packet as well as specifying a generic outgoing interface by the IPV6_PKTINFO sticky option, the latter will override the former for every multicast packet on the corresponding socket. The reason for the ordering comes from expectation that the source address is specified as well and that the pair of the address and the outgoing interface should be desired. When the IPV6_RECVPKTINFO socket option is enabled, the received interface index is always returned as the ipi6_ifindex member of the in6_pktinfo structure. 6.2. Specifying/Receiving Source/Destination Address The source IPv6 address can be specified by calling bind() before each output operation, but supplying the source address together with the data requires less overhead (i.e., fewer system calls) and requires less state to be stored and protected in a multithreaded application. When specifying the source IPv6 address as ancillary data, if the ipi6_addr member of the in6_pktinfo structure is the unspecified address (IN6ADDR_ANY_INIT or in6addr_any), then (a) if an address is currently bound to the socket, it is used as the source address, or (b) if no address is currently bound to the socket, the kernel will choose the source address. If the ipi6_addr member is not the unspecified address, but the socket has already bound a source address, then the ipi6_addr value overrides the already-bound source address for this output operation only. The kernel must verify that the requested source address is indeed a unicast address assigned to the node. When the address is a scoped one, there may be ambiguity about its scope zone. This is particularly the case for link-local addresses. In such a case, the kernel must first determine the appropriate scope zone based on the zone of the destination address or the outgoing interface (if known), then qualify the address. This also means that it is not feasible to specify the source address for a non-binding socket by the IPV6_PKTINFO sticky option, unless the outgoing interface is also specified. The application should simply use bind() for such purposes. IPV6_PKTINFO can also be used as a sticky option for specifying the socket's default source address. However, the ipi6_addr member draft-ietf-ipngwg-rfc2292bis-03.txt [Page 30]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 should be ignored when the option is specified for a TCP socket, because it is not possible to dynamically change the source address of a TCP connection. This restriction should be applied even before the socket binds a specific address. When the in6_pktinfo structure is returned as ancillary data by recvmsg(), the ipi6_addr member contains the destination IPv6 address from the received packet. For TCP sockets, the destination address will be trivial; the local address of the connection. 6.3. Specifying/Receiving the Hop Limit The outgoing hop limit is normally specified with either the IPV6_UNICAST_HOPS socket option or the IPV6_MULTICAST_HOPS socket option, both of which are described in [RFC-2553]. Specifying the hop limit as ancillary data lets the application override either the kernel's default or a previously specified value, for either a unicast destination or a multicast destination, for a single output operation. Returning the received hop limit is useful for programs such as Traceroute and for IPv6 applications that need to verify that the received hop limit is 255 (e.g., that the packet has not been forwarded). The received hop limit is returned as ancillary data by recvmsg() only if the application has enabled the IPV6_RECVHOPLIMIT socket option: int on = 1; setsockopt(fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &on, sizeof(on)); In the cmsghdr structure containing this ancillary data, the cmsg_level member will be IPPROTO_IPV6, the cmsg_type member will be IPV6_HOPLIMIT, and the first byte of cmsg_data[] will be the first byte of the integer hop limit. Nothing special need be done to specify the outgoing hop limit: just specify the control information as ancillary data for sendmsg(). As specified in [RFC-2553], the interpretation of the integer hop limit value is x < -1: return an error of EINVAL x == -1: use kernel default 0 <= x <= 255: use x x >= 256: return an error of EINVAL This API defines IPV6_HOPLIMIT as an ancillary-only option, that is, draft-ietf-ipngwg-rfc2292bis-03.txt [Page 31]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 the option name cannot be used as a socket option. This is because the basic API has more fine-grained socket options; IPV6_UNICAST_HOPS and IPV6_MULTICAST_HOPS. 6.4. Specifying the Next Hop Address The IPV6_NEXTHOP ancillary data object specifies the next hop for the datagram as a socket address structure. In the cmsghdr structure containing this ancillary data, the cmsg_level member will be IPPROTO_IPV6, the cmsg_type member will be IPV6_NEXTHOP, and the first byte of cmsg_data[] will be the first byte of the socket address structure. This is a privileged option. (Note: It is implementation defined and beyond the scope of this document to define what "privileged" means. Unix systems use this term to mean the process must have an effective user ID of 0.) This API only defines the case where the socket address contains an IPv6 address (i.e., the sa_family member is AF_INET6). And, in this case, the node identified by that address must be a neighbor of the sending host. If that address equals the destination IPv6 address of the datagram, then this is equivalent to the existing SO_DONTROUTE socket option. This option does not have any meaning for multicast destinations. In such a case, the specified next hop will be ignored. When the outgoing interface is specified by IPV6_PKTINFO as well, the next hop specified by this option must be reachable via the specified interface. In order to clear a sticky IPV6_NEXTHOP option the application must issue a setsockopt for IPV6_NEXTHOP with a zero length. 6.5. Specifying/Receiving the Traffic Class value The outgoing traffic class is normally set to 0. Specifying the traffic class as ancillary data lets the application override either the kernel's default or a previously specified value, for either a unicast destination or a multicast destination, for a single output operation. Returning the received traffic class is useful for programs such as a diffserv debugging tool and for user level ECN (explicit congestion notification) implementation. The received traffic class is returned as ancillary data by recvmsg() draft-ietf-ipngwg-rfc2292bis-03.txt [Page 32]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 only if the application has enabled the IPV6_RECVTCLASS socket option: int on = 1; setsockopt(fd, IPPROTO_IPV6, IPV6_RECVTCLASS, &on, sizeof(on)); In the cmsghdr structure containing this ancillary data, the cmsg_level member will be IPPROTO_IPV6, the cmsg_type member will be IPV6_TCLASS, and the first byte of cmsg_data[] will be the first byte of the integer traffic class. To specify the outgoing traffic class value, just specify the control information as ancillary data for sendmsg() or using setsockopt(). Just like the hop limit value, the interpretation of the integer traffic class value is x < -1: return an error of EINVAL x == -1: use kernel default 0 <= x <= 255: use x x >= 256: return an error of EINVAL In order to clear a sticky IPV6_TCLASS option the application can specify -1 as the value. There are cases where the kernel needs to control the traffic class value and conflicts with the user-specified value on the outgoing traffic. An example is an implementation of ECN in the kernel, setting 2 bits of the traffic class value. In such cases, the kernel should override the user-specified value. On the incoming traffic, the kernel may mask some of the bits in the traffic class field. 6.6. Additional Errors with sendmsg() and setsockopt() With the IPV6_PKTINFO socket option there are no additional errors possible with the call to recvmsg(). But when specifying the outgoing interface or the source address, additional errors are possible from sendmsg() or setsockopt(). Note that some implementations might only be able to return this type of errors for setsockopt(). The following are examples, but some of these may not be provided by some implementations, and some implementations may define additional errors: ENXIO The interface specified by ipi6_ifindex does not exist. ENETDOWN The interface specified by ipi6_ifindex is not enabled for IPv6 use. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 33]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 EADDRNOTAVAIL ipi6_ifindex specifies an interface but the address ipi6_addr is not available for use on that interface. EHOSTUNREACH No route to the destination exists over the interface specified by ifi6_ifindex. 6.7. Summary of outgoing interface selection This document and [RFC-2553] specify various methods that affect the selection of the packet's outgoing interface. This subsection summarizes the ordering among those in order to ensure determined behavior. For a given outgoing packet on a given socket, the outgoing interface is determined in the following order: 1. if an interface is specified in an IPV6_PKTINFO ancillary data item, the interface is used. 2. otherwise, if an interface is specified in an IPV6_PKTINFO sticky option, the interface is used. 3. otherwise, if the destination address is a multicast address and the IPV6_MULTICAST_IF socket option is specified for the socket, the interface is used. 4. otherwise, if an IPV6_NEXTHOP ancillary data item is specified, the interface to the next hop is used. 5. otherwise, if an IPV6_NEXTHOP sticky option is specified, the interface to the next hop is used. 6. otherwise, the outgoing interface should be determined in an implementation dependent manner. In any case, the kernel must also verify that the source and destination addresses do not break their scope zones with regard to the outgoing interface. 7. Routing Header Option Source routing in IPv6 is accomplished by specifying a Routing header as an extension header. There can be different types of Routing headers, but IPv6 currently defines only the Type 0 Routing header [RFC-2460]. This type supports up to 127 intermediate nodes (limited by the length field in the extension header). With this maximum number of intermediate nodes, a source, and a destination, there are 128 hops. Source routing with IPv4 sockets API (the IP_OPTIONS socket option) requires the application to build the source route in the format that draft-ietf-ipngwg-rfc2292bis-03.txt [Page 34]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 appears as the IPv4 header option, requiring intimate knowledge of the IPv4 options format. This IPv6 API, however, defines six functions that the application calls to build and examine a Routing header, and the ability to use sticky options or ancillary data to communicate this information between the application and the kernel using the IPV6_RTHDR option. Three functions build a Routing header: inet6_rth_space() - return #bytes required for Routing header inet6_rth_init() - initialize buffer data for Routing header inet6_rth_add() - add one IPv6 address to the Routing header Three functions deal with a returned Routing header: inet6_rth_reverse() - reverse a Routing header inet6_rth_segments() - return #segments in a Routing header inet6_rth_getaddr() - fetch one address from a Routing header The function prototypes for these functions are defined as a result of including the <netinet/in.h>. To receive a Routing header the application must enable the IPV6_RECVRTHDR socket option: int on = 1; setsockopt(fd, IPPROTO_IPV6, IPV6_RECVRTHDR, &on, sizeof(on)); Each received Routing header is returned as one ancillary data object described by a cmsghdr structure with cmsg_type set to IPV6_RTHDR. When multiple Routing headers are received, multiple ancillary data objects (with cmsg_type set to IPV6_RTHDR) will be returned to the application. To send a Routing header the application specifies it either as ancillary data in a call to sendmsg() or using setsockopt(). For the sending side, this API assumes the recommended order about extension headers described in [RFC-2460]. Thus, applications can only specify at most one outgoing Routing header. The application can remove any sticky Routing header by calling setsockopt() for IPV6_RTHDR with a zero option length. When using ancillary data a Routing header is passed between the application and the kernel as follows: The cmsg_level member has a value of IPPROTO_IPV6 and the cmsg_type member has a value of IPV6_RTHDR. The contents of the cmsg_data[] member is implementation dependent and should not be accessed directly by the application, but draft-ietf-ipngwg-rfc2292bis-03.txt [Page 35]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 should be accessed using the six functions that we are about to describe. The following constant is defined as a result of including the <netinet/in.h>: #define IPV6_RTHDR_TYPE_0 0 /* IPv6 Routing header type 0 */ When a Routing header is specified, the destination address specified for connect(), sendto(), or sendmsg() is the final destination address of the datagram. The Routing header then contains the addresses of all the intermediate nodes. 7.1. inet6_rth_space size_t inet6_rth_space(int type, int segments); This function returns the number of bytes required to hold a Routing header of the specified type containing the specified number of segments (addresses). For an IPv6 Type 0 Routing header, the number of segments must be between 0 and 127, inclusive. The return value is just the space for the Routing header. When the application uses ancillary data it must pass the returned length to CMSG_LEN() to determine how much memory is needed for the ancillary data object (including the cmsghdr structure). If the return value is 0, then either the type of the Routing header is not supported by this implementation or the number of segments is invalid for this type of Routing header. (Note: This function returns the size but does not allocate the space required for the ancillary data. This allows an application to allocate a larger buffer, if other ancillary data objects are desired, since all the ancillary data objects must be specified to sendmsg() as a single msg_control buffer.) 7.2. inet6_rth_init void *inet6_rth_init(void *bp, int bp_len, int type, int segments); This function initializes the buffer pointed to by bp to contain a Routing header of the specified type and sets ip6r_len based on the segments parameter. bp_len is only used to verify that the buffer is large enough. The ip6r_segleft field is set to zero; inet6_rth_add() draft-ietf-ipngwg-rfc2292bis-03.txt [Page 36]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 will increment it. When the application uses ancillary data the application must initialize any cmsghdr fields. The caller must allocate the buffer and its size can be determined by calling inet6_rth_space(). Upon success the return value is the pointer to the buffer (bp), and this is then used as the first argument to the inet6_rth_add() function. Upon an error the return value is NULL. 7.3. inet6_rth_add int inet6_rth_add(void *bp, const struct in6_addr *addr); This function adds the IPv6 address pointed to by addr to the end of the Routing header being constructed. If successful, the segleft member of the Routing Header is updated to account for the new address in the Routing header and the return value of the function is 0. Upon an error the return value of the function is -1. 7.4. inet6_rth_reverse int inet6_rth_reverse(const void *in, void *out); This function takes a Routing header extension header (pointed to by the first argument) and writes a new Routing header that sends datagrams along the reverse of that route. The function reverses the order of the addresses and sets the segleft member in the new Routing header to the number of segments. Both arguments are allowed to point to the same buffer (that is, the reversal can occur in place). The return value of the function is 0 on success, or -1 upon an error. 7.5. inet6_rth_segments int inet6_rth_segments(const void *bp); draft-ietf-ipngwg-rfc2292bis-03.txt [Page 37]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 This function returns the number of segments (addresses) contained in the Routing header described by bp. On success the return value is zero or greater. The return value of the function is -1 upon an error. 7.6. inet6_rth_getaddr struct in6_addr *inet6_rth_getaddr(const void *bp, int index); This function returns a pointer to the IPv6 address specified by index (which must have a value between 0 and one less than the value returned by inet6_rth_segments()) in the Routing header described by bp. An application should first call inet6_rth_segments() to obtain the number of segments in the Routing header. Upon an error the return value of the function is NULL. 8. Hop-By-Hop Options A variable number of Hop-by-Hop options can appear in a single Hop- by-Hop options header. Each option in the header is TLV-encoded with a type, length, and value. This IPv6 API defines seven functions that the application calls to build and examine a Hop-by_Hop options header, and the ability to use sticky options or ancillary data to communicate this information between the application and the kernel. This uses the IPV6_HOPOPTS for a Hob-by-Hop options header. Today several Hop-by-Hop options are defined for IPv6. Two pad options, Pad1 and PadN, are for alignment purposes and are automatically inserted by the inet6_opt_XXX() routines and ignored by the inet6_opt_XXX() routines on the receive side. This section of the API is therefore defined for other (and future) Hop-by-Hop options that an application may need to specify and receive. Four functions build an options header: inet6_opt_init() - initialize buffer data for options header inet6_opt_append() - add one TLV option to the options header inet6_opt_finish() - finish adding TLV options to the options header inet6_opt_set_val() - add one component of the option content to the option Three functions deal with a returned options header: draft-ietf-ipngwg-rfc2292bis-03.txt [Page 38]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 inet6_opt_next() - extract the next option from the options header inet6_opt_find() - extract an option of a specified type from the header inet6_opt_get_val() - retrieve one component of the option content Individual Hop-by-Hop options (and Destination options, which are described in Section 9 and are very similar to the Hop-by-Hop options) may have specific alignment requirements. For example, the 4-byte Jumbo Payload length should appear on a 4-byte boundary, and IPv6 addresses are normally aligned on an 8-byte boundary. These requirements and the terminology used with these options are discussed in Section 4.2 and Appendix B of [RFC-2460]. The alignment of first byte of each option is specified by two values, called x and y, written as "xn + y". This states that the option must appear at an integer multiple of x bytes from the beginning of the options header (x can have the values 1, 2, 4, or 8), plus y bytes (y can have a value between 0 and 7, inclusive). The Pad1 and PadN options are inserted as needed to maintain the required alignment. The functions below need to know the alignment of the end of the option (which is always in the form "xn," where x can have the values 1, 2, 4, or 8) and the total size of the data portion of the option. These are passed as the "align" and "len" arguments to inet6_opt_append(). Multiple Hop-by-Hop options must be specified by the application by placing them in a single extension header. Finally, we note that use of some Hop-by-Hop options or some Destination options, might require special privilege. That is, normal applications (without special privilege) might be forbidden from setting certain options in outgoing packets, and might never see certain options in received packets. 8.1. Receiving Hop-by-Hop Options To receive a Hop-by-Hop options header the application must enable the IPV6_RECVHOPOPTS socket option: int on = 1; setsockopt(fd, IPPROTO_IPV6, IPV6_RECVHOPOPTS, &on, sizeof(on)); When using ancillary data a Hop-by-hop options header is passed between the application and the kernel as follows: The cmsg_level member will be IPPROTO_IPV6 and the cmsg_type member will be IPV6_HOPOPTS. These options are then processed by calling the inet6_opt_next(), inet6_opt_find(), and inet6_opt_get_val() draft-ietf-ipngwg-rfc2292bis-03.txt [Page 39]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 functions, described in Section 10. 8.2. Sending Hop-by-Hop Options To send a Hop-by-Hop options header, the application specifies the header either as ancillary data in a call to sendmsg() or using setsockopt(). The application can remove any sticky Hop-by-Hop options header by calling setsockopt() for IPV6_HOPOPTS with a zero option length. All the Hop-by-Hop options must be specified by a single ancillary data object. The cmsg_level member is set to IPPROTO_IPV6 and the cmsg_type member is set to IPV6_HOPOPTS. The option is normally constructed using the inet6_opt_init(), inet6_opt_append(), inet6_opt_finish(), and inet6_opt_set_val() functions, described in Section 10. Additional errors may be possible from sendmsg() and setsockopt() if the specified option is in error. 9. Destination Options A variable number of Destination options can appear in one or more Destination options headers. As defined in [RFC-2460], a Destination options header appearing before a Routing header is processed by the first destination plus any subsequent destinations specified in the Routing header, while a Destination options header that is not followed by a Routing header is processed only by the final destination. As with the Hop-by-Hop options, each option in a Destination options header is TLV-encoded with a type, length, and value. 9.1. Receiving Destination Options To receive Destination options header the application must enable the IPV6_RECVDSTOPTS socket option: int on = 1; setsockopt(fd, IPPROTO_IPV6, IPV6_RECVDSTOPTS, &on, sizeof(on)); 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. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 40]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 These options are then processed by calling the inet6_opt_next(), inet6_opt_find(), and inet6_opt_get_value() functions. 9.2. Sending Destination Options To send a Destination options header, the application specifies it either as ancillary data in a call to sendmsg() or using setsockopt(). The application can remove any sticky Destination options header by calling setsockopt() for IPV6_RTHDRDSTOPTS/IPV6_DSTOPTS with a zero option length. This API assumes the recommended ordering about extension headers described in [RFC-2460]. Thus, one set of Destination options can only appear before a Routing header, and one set can only appear after a Routing header (or in a packet with no Routing header). Each set can consist of one or more options but each set is a single extension header. When using ancillary data a Destination options header is passed between the application and the kernel as follows: The set preceding a Routing header are specified with the cmsg_level member set to IPPROTO_IPV6 and the cmsg_type member set to IPV6_RTHDRDSTOPTS. Any setsockopt or ancillary data for IPV6_RTHDRDSTOPTS is silently ignored when sending packets unless a Routing header is also specified. Note that the "Routing header" here means the one specified by this API. Even when the kernel inserts a routing header in its internal routine (e.g. in a mobile IPv6 stack), the Destination options header specified by IPV6_RTHDRDSTOPTS will still be ignored unless the application explicitly specifies its own Routing header. The set of Destination options after a Routing header, which are also used when no Routing header is present, are specified with the cmsg_level member is set to IPPROTO_IPV6 and the cmsg_type member is set to IPV6_DSTOPTS. The Destination options are normally constructed using the inet6_opt_init(), inet6_opt_append(), inet6_opt_finish(), and inet6_opt_set_val() functions, described in Section 10. Additional errors may be possible from sendmsg() and setsockopt() if the specified option is in error. 10. Hop-by-Hop and Destination Options Processing draft-ietf-ipngwg-rfc2292bis-03.txt [Page 41]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 Building and parsing the Hop-by-Hop and Destination options is complicated for the reasons given earlier. We therefore define a set of functions to help the application. These functions assume the formatting rules specified in Appendix B in [RFC-2460] i.e. that the largest field is placed last in the option. The function prototypes for these functions are defined as a result of including the <netinet/in.h>. The first 3 functions (init, append, and finish) are used both to calculate the needed buffer size for the options, and to actually encode the options once the application has allocated a buffer for the header. In order to only calculate the size the application must pass a NULL extbuf and a zero extlen to those functions. 10.1. inet6_opt_init int inet6_opt_init(void *extbuf, size_t extlen); This function returns the number of bytes needed for the empty extension header i.e. without any options. If extbuf is not NULL it also initializes the extension header to have the correct length field. In that case if the extlen value is not a positive (i.e., non-zero) multiple of 8 the function fails and returns -1. 10.2. inet6_opt_append int inet6_opt_append(void *extbuf, size_t extlen, int prevlen, uint8_t type, size_t len, uint_t align, void **databufp); Prevlen should be the length returned by inet6_opt_init() or a previous inet6_opt_append(). This function returns the updated total length taking into account adding an option with length 'len' and alignment 'align'. If extbuf is not NULL then, in addition to returning the length, the function inserts any needed pad option, initializes the option (setting the type and length fields) and returns a pointer to the location for the option content in databufp. If the option does not fit in the extension header buffer the function returns -1. Type is the 8-bit option type. Len is the length of the option data (i.e. excluding the option type and option length fields). draft-ietf-ipngwg-rfc2292bis-03.txt [Page 42]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 Once inet6_opt_append() has been called the application can use the databuf directly, or use inet6_opt_set_val() to specify the content of the option. The option type must have a value from 2 to 255, inclusive. (0 and 1 are reserved for the Pad1 and PadN options, respectively.) The option data length must have a value between 0 and 255, inclusive, and is the length of the option data that follows. The align parameter must have a value of 1, 2, 4, or 8. The align value can not exceed the value of len. 10.3. inet6_opt_finish int inet6_opt_finish(void *extbuf, size_t extlen, int prevlen); Prevlen should be the length returned by inet6_opt_init() or inet6_opt_append(). This function returns the updated total length taking into account the final padding of the extension header to make it a multiple of 8 bytes. If extbuf is not NULL the function also initializes the option by inserting a Pad1 or PadN option of the proper length. If the necessary pad does not fit in the extension header buffer the function returns -1. 10.4. inet6_opt_set_val int inet6_opt_set_val(void *databuf, size_t offset, void *val, int vallen); Databuf should be a pointer returned by inet6_opt_append(). This function inserts data items of various sizes in the data portion of the option. Val should point to the data to be inserted. Offset specifies where in the data portion of the option the value should be inserted; the first byte after the option type and length is accessed by specifying an offset of zero. The caller should ensure that each field is aligned on its natural boundaries as described in Appendix B of [RFC-2460], but the function must not rely on the caller's behavior. Even when the alignment requirement is not satisfied, inet6_opt_set_val should just copy the data as required. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 43]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 The function returns the offset for the next field (i.e., offset + vallen) which can be used when composing option content with multiple fields. 10.5. inet6_opt_next int inet6_opt_next(void *extbuf, size_t extlen, int prevlen, uint8_t *typep, size_t *lenp, void **databufp); This function parses received option extension headers returning the next option. Extbuf and extlen specifies the extension header. Prevlen should either be zero (for the first option) or the length returned by a previous call to inet6_opt_next() or inet6_opt_find(). It specifies the position where to continue scanning the extension buffer. The next option is returned by updating typep, lenp, and databufp. This function returns the updated "previous" length computed by advancing past the option that was returned. This returned "previous" length can then be passed to subsequent calls to inet6_opt_next(). This function does not return any PAD1 or PADN options. When there are no more options or if the option extension header is malformed the return value is -1. 10.6. inet6_opt_find int inet6_opt_find(void *extbuf, size_t extlen, int prevlen, uint8_t type, size_t *lenp, void **databufp); This function is similar to the previously described inet6_opt_next() function, except this function lets the caller specify the option type to be searched for, instead of always returning the next option in the extension header. If an option of the specified type is located, the function returns the updated "previous" total length computed by advancing past the option that was returned and past any options that didn't match the type. This returned "previous" length can then be passed to subsequent calls to inet6_opt_find() for finding the next occurrence of the same option type. If an option of the specified type is not located, the return value is -1. If the option extension header is malformed, the return value draft-ietf-ipngwg-rfc2292bis-03.txt [Page 44]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 is -1. 10.7. inet6_opt_get_val int inet6_opt_get_val(void *databuf, size_t offset, void *val, int vallen); Databuf should be a pointer returned by inet6_opt_next() or inet6_opt_find(). This function extracts data items of various sizes in the data portion of the option. Val should point to the destination for the extracted data. Offset specifies from where in the data portion of the option the value should be extracted; the first byte after the option type and length is accessed by specifying an offset of zero. It is expected that each field is aligned on its natural boundaries as described in Appendix B of [RFC-2460], but the function must not rely on the alignment. The function returns the offset for the next field (i.e., offset + vallen) which can be used when extracting option content with multiple fields. 11. Additional Advanced API Functions 11.1. Sending with the Minimum MTU Some applications might not want to incur the overhead of path MTU discovery, especially if the applications only send a single datagram to a destination. A potential example is a DNS server. This specification defines a mechanism to avoid path MTU discovery by sending at the minimum IPv6 MTU [RFC-2460]. If the packet is larger than the minimum MTU and this feature has been enabled the IP layer will fragment to the minimum MTU. This can be enabled using the IPV6_USE_MIN_MTU socket option. int on = 1; setsockopt(fd, IPPROTO_IPV6, IPV6_USE_MIN_MTU, &on, sizeof(on)); By default, this socket option is disabled. Setting the value to 0 also disables the option. This option can also be sent as ancillary data. In the cmsghdr structure containing this ancillary data, the draft-ietf-ipngwg-rfc2292bis-03.txt [Page 45]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 cmsg_level member will be IPPROTO_IPV6, the cmsg_type member will be IPV6_USE_MIN_MTU, and the first byte of cmsg_data[] will be the first byte of the integer. 11.2. Sending without fragmentation In order to provide for easy porting of existing UDP and raw socket applications IPv6 implementations will, when originating packets, automatically insert a fragment header in the packet if the packet is too big for the path MTU. Some applications might not want this behavior. An example is traceroute which might want to discover the actual path MTU. This specification defines a mechanism to turn off the automatic inserting of a fragment header for UDP and raw sockets. This can be enabled using the IPV6_DONTFRAG socket option. int on = 1; setsockopt(fd, IPPROTO_IPV6, IPV6_DONTFRAG, &on, sizeof(&on)); By default, this socket option is disabled. Setting the value to 0 also disables the option i.e. reverts to the default behavior of automatic inserting. This option can also be sent as ancillary data. In the cmsghdr structure containing this ancillary data, the cmsg_level member will be IPPROTO_IPV6, the cmsg_type member will be IPV6_DONTFRAG, and the first byte of cmsg_data[] will be the first byte of the integer. This API only specifies the use of this option for UDP and raw sockets, and does not define the usage for TCP sockets. When the data size is larger than the MTU of the outgoing interface, the packet will be discarded. Applications can know the result by enabling the IPV6_RECVPATHMTU option described below and receiving the corresponding ancillary data items. 11.3. Path MTU Discovery and UDP UDP and raw socket applications need to be able to determine the "maximum send transport-message size" (Section 5.1 of [RFC-1981]) to a given destination so that those applications can participate in path MTU discovery. This lets those applications send smaller datagrams to the destination, avoiding fragmentation. This is accomplished using a new ancillary data item (IPV6_PATHMTU) which is delivered to recvmsg() without any actual data. The draft-ietf-ipngwg-rfc2292bis-03.txt [Page 46]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 application can enable the receipt of IPV6_PATHMTU ancillary data items by setting the IPV6_RECVPATHMTU socket option. int on = 1; setsockopt(fd, IPPROTO_IPV6, IPV6_RECVPATHMTU, &on, sizeof(on)); By default, this socket option is disabled. Setting the value to 0 also disables the option. This API only specifies the use of this option for UDP and raw sockets, and does not define the usage for TCP sockets. When the application is sending packets too big for the path MTU recvmsg will return zero (indicating no data) but there will be a cmsghdr with cmsg_type set to IPV6_PATHMTU, and cmsg_len will indicate that cmsg_data is sizeof(struct ip6_mtuinfo) bytes long. This can happen when the sending node receives a corresponding ICMPv6 packet too big error, or when the packet is sent from a socket with the IPV6_DONTFRAG option being on and the packet size is larger than the MTU of the outgoing interface. The first byte of cmsg_data[] will point to a struct ip6_mtuinfo carrying the path MTU to use together with the IPv6 destination address. struct ip6_mtuinfo { struct sockaddr_in6 ip6m_addr; /* dst address including zone ID */ uint32_t ip6m_mtu; /* path MTU in host byte order */ }; This cmsghdr will be passed to every socket that sets the IPV6_RECVPATHMTU socket option, even if the socket is non-connected. Note that this also means an application that sets the option may get the ancillary data upon a too big message sent from other applications to the same destination. An implementation may choose not to delivery data to a connected socket that has a foreign address that is different than the address specified in the ip6m_addr structure. When an application sends a packet with a routing header, the final destination stored in the ip6m_addr member does not necessarily contain complete information of the entire path. 11.4. Determining the current path MTU Some applications might need to determine the current path MTU e.g. applications using IPV6_RECVPATHMTU might want to pick a good starting value. This specification defines a get-only socket option to retrieve the draft-ietf-ipngwg-rfc2292bis-03.txt [Page 47]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 current path MTU value for the destination of a given connected socket. If the IP layer does not have a cached path MTU value it will return the interface MTU for the interface that will be used when sending to the destination address. This information is retrieved using the IPV6_PATHMTU socket option. This option takes a pointer to the ip6_mtuinfo structure as the fourth argument, and the size of the structure should be passed as a value-result parameter in the fifth argument. struct ip6_mtuinfo mtuinfo; size_t infolen = sizeof(mtuinfo); getsockopt(fd, IPPROTO_IPV6, IPV6_PATHMTU, &mtuinfo, &infolen); When the call succeeds, the path MTU value is stored in the ip6m_mtu member of the ip6_mtuinfo structure. Since the socket is connected, the ip6m_addr member is meaningless and should not be referred to by the application. This option can only be used for a connected socket, because a non- connected socket does not have the information of the destination and there is no way to pass the destination via getsockopt(). When getsockopt() for this option is issued on a non-connected socket, the call will fail. 11.5. Neighbor Reachability and UDP UDP and raw socket applications might know that communication is making forward progress i.e. that the path from the node to the next hop is working. In such a case the applications, similarly to TCP as specified in [RFC-2461], has the option indicate to the internet layer that the neighbor is reachable. See section 7.3.1 of [RFC- 2461]. This could save unneeded neighbor solicitation and neighbor advertisement messages. This is done by including an ancillary data item with cmsg_type being IPV6_REACHCONF and with no attached CMSG_DATA. IPV6_REACHCONF can only be used as an ancillary data item. This also means that this cannot be used for TCP sockets. If implementations honor the IPV6_REACHCONF from any application there is a possibility that, when there is an unreachability situation, one application can cause a denial of service attack on anogther application running on the same node by periodically issuing sendmsg() with an IPV6_REACHCONF ancillary data item to prevent the Neighbor Unreachability Detection algoritm to send probe messages and draft-ietf-ipngwg-rfc2292bis-03.txt [Page 48]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 declare the neighbor unreachable. It is unclear whether implementations need to mitigate this very minor threat by e.g. restricting IPV6_REACHCONF to priviledged applications. 12. Ordering of Ancillary Data and IPv6 Extension Headers Three IPv6 extension headers can be specified by the application and returned to the application using ancillary data with sendmsg() and recvmsg(): the Routing header, Hop-by-Hop options header, and Destination options header. When multiple ancillary data objects are transferred via recvmsg() and these objects represent any of these three extension headers, their placement in the control buffer is directly tied to their location in the corresponding IPv6 datagram. For example, when the application has enabled the IPV6_RECVRTHDR and IPV6_RECVDSTOPTS options and later receives an IPv6 packet with extension headers in the following order: The IPv6 header A Hop-by-Hop options header A Destination options header (1) A Routing header An Authentication header A Destination options header (2) A UDP header and UDP data then the application will receive three ancillary data objects in the following order: an object with cmsg_type set to IPV6_DSTOPTS, which represents the destination options header (1) an object with cmsg_type set to IPV6_DSTOPTS, which represents the Routing header an object with cmsg_type set to IPV6_DSTOPTS, which represents the destination options header (2) This example follows the recommended order described in [RFC-2460], but the receiving side of this specification does not assume the recommended order. Applications may receive any numbers of objects in any order according to the ordering of the received IPv6 datagram. For the sending side, however, this API imposes some ordering constraints according to the recommendation. Applications using this API cannot make a packet with extension headers that do not follow the recommended ordering. Should an application need to make an outgoing packet in an arbitrary order about the extension headers, some other technique, such as the datalink interfaces BPF or DLPI, must be used. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 49]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 The followings are more details about the constraints: - Each IPV6_xxx ancillary data object for a particular type of extension header can be specified at most once in a single control buffer. - IPV6_xxx ancillary data objects can appear in any order in a control buffer, because there is no ambiguity of the ordering. - Each set of IPV6_xxx ancillary data objects and sticky options will be put in the outgoing packet along with the recommended header ordering described in [RFC-2460]. - An ancillary data object or a sticky option of IPV6_RTHDRDSTOPTS will affect the outgoing packet only when a Routing header is specified as an ancillary data object or a sticky option. Otherwise, the specified value for IPV6_RTHDRDSTOPTS will be ignored. For example, when an application sends a UDP datagram with a control data buffer containing ancillary data objects in the following order: an object with cmsg_type set to IPV6_DSTOPTS an object with cmsg_type set to IPV6_RTHDRDSTOPTS an object with cmsg_type set to IPV6_HOPOPTS and the sending socket does not have any sticky options, then the outgoing packet would be constructed as follows: The IPv6 header A Hop-by-Hop options header A Destination options header A UDP header and UDP data where the destination options header corresponds to the ancillary data object with the type IPV6_DSTOPTS. Note that the constraints above do not necessarily mean that the outgoing packet sent on the wire always follows the recommended header ordering. The kernel may insert additional headers that break the recommended order as a result. For example, if the kernel supports Mobile IPv6, an additional destination options header may be inserted before an authentication header, even without a routing header. This API does not provide access to any other extension headers than the supported three types of headers. In particular, no information is provided about the IP security headers on an incoming packet, nor draft-ietf-ipngwg-rfc2292bis-03.txt [Page 50]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 can be specified for an outgoing packet. This API is for applications that do not care about the existence of IP security headers. 13. IPv6-Specific Options with 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. In general, attempting to specify an IPv6-only option, such as the Hop-by-Hop options, Destination options, or Routing header on an IPv6 socket that is using IPv4-mapped IPv6 addresses, will probably result in an error. Some implementations, however, may provide access to the packet information (source/destination address, send/receive interface, and hop limit) on an IPv6 socket that is using IPv4-mapped IPv6 addresses. 14. Extended interfaces for rresvport, rcmd and rexec TBD 14.1. rresvport_af The rresvport() function is used by the rcmd() function, and this function is in turn called by many of the "r" commands such as rlogin. While new applications are not being written to use the rcmd() function, legacy applications such as rlogin will continue to use it and these will be ported to IPv6. rresvport() creates an IPv4/TCP socket and binds a "reserved port" to the socket. Instead of defining an IPv6 version of this function we define a new function that takes an address family as its argument. #include <unistd.h> int rresvport_af(int *port, int family); This function behaves the same as the existing rresvport() function, but instead of creating an AF_INET TCP socket, it can also create an AF_INET6 TCP socket. The family argument is either AF_INET or AF_INET6, and a new error return is EAFNOSUPPORT if the address draft-ietf-ipngwg-rfc2292bis-03.txt [Page 51]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 family is not supported. (Note: There is little consensus on which header defines the rresvport() and rcmd() function prototypes. 4.4BSD defines it in <unistd.h>, others in <netdb.h>, and others don't define the function prototypes at all.) 14.2. rcmd_af The existing rcmd() function can not transparently use AF_INET6 sockets since an application would not be prepared to handle AF_INET6 addresses returned by e.g. getpeername on the file descriptor created by rcmd. Thus a new function is needed. int rcmd_af(char **ahost, unsigned short rport, const char *locuser, const char *remuser, const char *cmd, int *fd2p, int af) This function behaves the same as the existing rcmd() function, but instead of creating an AF_INET TCP socket, it can also create an AF_INET6 TCP socket. The family argument is either AF_INET or AF_INET6, and a new error return is EAFNOSUPPORT if the address family is not supported. 14.3. rexec_af The existing rexec() function can not transparently use AF_INET6 sockets since the an application would not be prepared to handle AF_INET6 addresses returned by e.g. getpeername on the file descriptor created by rexec. Thus a new function is needed. int rexec_af(char **ahost, unsigned short rport, const char *name, const char *pass, const char *cmd, int *fd2p, int af) This function behaves the same as the existing rexec() function, but instead of creating an AF_INET TCP socket, it can also create an AF_INET6 TCP socket. The family argument is either AF_INET or AF_INET6, and a new error return is EAFNOSUPPORT if the address family is not supported. 15. Summary of New Definitions The following list summarizes the constants and structure, definitions discussed in this memo, sorted by header. <netinet/icmp6.h> ICMP6_DST_UNREACH draft-ietf-ipngwg-rfc2292bis-03.txt [Page 52]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 <netinet/icmp6.h> ICMP6_DST_UNREACH_ADDR <netinet/icmp6.h> ICMP6_DST_UNREACH_ADMIN <netinet/icmp6.h> ICMP6_DST_UNREACH_BEYONDSCOPE <netinet/icmp6.h> ICMP6_DST_UNREACH_NOPORT <netinet/icmp6.h> ICMP6_DST_UNREACH_NOROUTE <netinet/icmp6.h> ICMP6_ECHO_REPLY <netinet/icmp6.h> ICMP6_ECHO_REQUEST <netinet/icmp6.h> ICMP6_INFOMSG_MASK <netinet/icmp6.h> ICMP6_PACKET_TOO_BIG <netinet/icmp6.h> ICMP6_PARAMPROB_HEADER <netinet/icmp6.h> ICMP6_PARAMPROB_NEXTHEADER <netinet/icmp6.h> ICMP6_PARAMPROB_OPTION <netinet/icmp6.h> ICMP6_PARAM_PROB <netinet/icmp6.h> ICMP6_ROUTER_RENUMBERING <netinet/icmp6.h> ICMP6_RR_FLAGS_FORCEAPPLY <netinet/icmp6.h> ICMP6_RR_FLAGS_PREVDONE <netinet/icmp6.h> ICMP6_RR_FLAGS_REQRESULT <netinet/icmp6.h> ICMP6_RR_FLAGS_SPECSITE <netinet/icmp6.h> ICMP6_RR_FLAGS_TEST <netinet/icmp6.h> ICMP6_RR_PCOUSE_FLAGS_DECRPLTIME <netinet/icmp6.h> ICMP6_RR_PCOUSE_FLAGS_DECRVLTIME <netinet/icmp6.h> ICMP6_RR_PCOUSE_RAFLAGS_AUTO <netinet/icmp6.h> ICMP6_RR_PCOUSE_RAFLAGS_ONLINK <netinet/icmp6.h> ICMP6_RR_RESULT_FLAGS_FORBIDDEN <netinet/icmp6.h> ICMP6_RR_RESULT_FLAGS_OOB <netinet/icmp6.h> ICMP6_TIME_EXCEEDED <netinet/icmp6.h> ICMP6_TIME_EXCEED_REASSEMBLY <netinet/icmp6.h> ICMP6_TIME_EXCEED_TRANSIT <netinet/icmp6.h> MLD_LISTENER_QUERY <netinet/icmp6.h> MLD_LISTENER_REDUCTION <netinet/icmp6.h> MLD_LISTENER_REPORT <netinet/icmp6.h> ND_NA_FLAG_OVERRIDE <netinet/icmp6.h> ND_NA_FLAG_ROUTER <netinet/icmp6.h> ND_NA_FLAG_SOLICITED <netinet/icmp6.h> ND_NEIGHBOR_ADVERT <netinet/icmp6.h> ND_NEIGHBOR_SOLICIT <netinet/icmp6.h> ND_OPT_MTU <netinet/icmp6.h> ND_OPT_PI_FLAG_AUTO <netinet/icmp6.h> ND_OPT_PI_FLAG_ONLINK <netinet/icmp6.h> ND_OPT_PI_FLAG_ROUTER <netinet/icmp6.h> ND_OPT_PREFIX_INFORMATION <netinet/icmp6.h> ND_OPT_REDIRECTED_HEADER <netinet/icmp6.h> ND_OPT_SOURCE_LINKADDR <netinet/icmp6.h> ND_OPT_TARGET_LINKADDR <netinet/icmp6.h> ND_RA_FLAG_MANAGED <netinet/icmp6.h> ND_RA_FLAG_OTHER <netinet/icmp6.h> ND_REDIRECT <netinet/icmp6.h> ND_ROUTER_ADVERT draft-ietf-ipngwg-rfc2292bis-03.txt [Page 53]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 <netinet/icmp6.h> ND_ROUTER_SOLICIT <netinet/icmp6.h> struct icmp6_filter{}; <netinet/icmp6.h> struct icmp6_hdr{}; <netinet/icmp6.h> struct icmp6_router_renum{}; <netinet/icmp6.h> struct mld_hdr{}; <netinet/icmp6.h> struct nd_neighbor_advert{}; <netinet/icmp6.h> struct nd_neighbor_solicit{}; <netinet/icmp6.h> struct nd_opt_hdr{}; <netinet/icmp6.h> struct nd_opt_mtu{}; <netinet/icmp6.h> struct nd_opt_prefix_info{}; <netinet/icmp6.h> struct nd_opt_rd_hdr{}; <netinet/icmp6.h> struct nd_redirect{}; <netinet/icmp6.h> struct nd_router_advert{}; <netinet/icmp6.h> struct nd_router_solicit{}; <netinet/icmp6.h> struct rr_pco_match{}; <netinet/icmp6.h> struct rr_pco_use{}; <netinet/icmp6.h> struct rr_result{}; <netinet/in.h> IPPROTO_AH <netinet/in.h> IPPROTO_DSTOPTS <netinet/in.h> IPPROTO_ESP <netinet/in.h> IPPROTO_FRAGMENT <netinet/in.h> IPPROTO_HOPOPTS <netinet/in.h> IPPROTO_ICMPV6 <netinet/in.h> IPPROTO_IPV6 <netinet/in.h> IPPROTO_NONE <netinet/in.h> IPPROTO_ROUTING <netinet/in.h> IPV6_CHECKSUM <netinet/in.h> IPV6_DONTFRAG <netinet/in.h> IPV6_DSTOPTS <netinet/in.h> IPV6_HOPLIMIT <netinet/in.h> IPV6_HOPOPTS <netinet/in.h> IPV6_NEXTHOP <netinet/in.h> IPV6_PATHMTU <netinet/in.h> IPV6_PKTOPTIONS <netinet/in.h> IPV6_PKTINFO <netinet/in.h> IPV6_RECVDSTOPTS <netinet/in.h> IPV6_RECVHOPLIMIT <netinet/in.h> IPV6_RECVHOPOPTS <netinet/in.h> IPV6_RECVPKTINFO <netinet/in.h> IPV6_RECVRTHDR <netinet/in.h> IPV6_RECVTCLASS <netinet/in.h> IPV6_RTHDR <netinet/in.h> IPV6_RTHDRDSTOPTS <netinet/in.h> IPV6_RTHDR_TYPE_0 <netinet/in.h> IPV6_RECVPATHMTU <netinet/in.h> IPV6_REACHCONF draft-ietf-ipngwg-rfc2292bis-03.txt [Page 54]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 <netinet/in.h> IPV6_TCLASS <netinet/in.h> IPV6_USE_MIN_MTU <netinet/in.h> struct in6_pktinfo{}; <netinet/in.h> struct ip6_mtuinfo{}; <netinet/ip6.h> IP6F_MORE_FRAG <netinet/ip6.h> IP6F_OFF_MASK <netinet/ip6.h> IP6F_RESERVED_MASK <netinet/ip6.h> IP6OPT_JUMBO <netinet/ip6.h> IP6OPT_JUMBO_LEN <netinet/ip6.h> IP6OPT_MUTABLE <netinet/ip6.h> IP6OPT_NSAP_ADDR <netinet/ip6.h> IP6OPT_PAD1 <netinet/ip6.h> IP6OPT_PADN <netinet/ip6.h> IP6OPT_ROUTER_ALERT <netinet/ip6.h> IP6OPT_TUNNEL_LIMIT <netinet/ip6.h> IP6OPT_TYPE_DISCARD <netinet/ip6.h> IP6OPT_TYPE_FORCEICMP <netinet/ip6.h> IP6OPT_TYPE_ICMP <netinet/ip6.h> IP6OPT_TYPE_SKIP <netinet/ip6.h> IP6_ALERT_AN <netinet/ip6.h> IP6_ALERT_MLD <netinet/ip6.h> IP6_ALERT_RSVP <netinet/ip6.h> struct ip6_dest{}; <netinet/ip6.h> struct ip6_ext{}; <netinet/ip6.h> struct ip6_frag{}; <netinet/ip6.h> struct ip6_hbh{}; <netinet/ip6.h> struct ip6_hdr{}; <netinet/ip6.h> struct ip6_opt{}; <netinet/ip6.h> struct ip6_opt_jumbo{}; <netinet/ip6.h> struct ip6_opt_nsap{}; <netinet/ip6.h> struct ip6_opt_router{}; <netinet/ip6.h> struct ip6_opt_tunnel{}; <netinet/ip6.h> struct ip6_rthdr{}; <netinet/ip6.h> struct ip6_rthdr0{}; The following list summarizes the function and macro prototypes discussed in this memo, sorted by header. <netinet/icmp6.h> void ICMP6_FILTER_SETBLOCK(int, struct icmp6_filter *); <netinet/icmp6.h> void ICMP6_FILTER_SETBLOCKALL(struct icmp6_filter *); <netinet/icmp6.h> void ICMP6_FILTER_SETPASS(int, struct icmp6_filter *); <netinet/icmp6.h> void ICMP6_FILTER_SETPASSALL(struct icmp6_filter *); <netinet/icmp6.h> int ICMP6_FILTER_WILLBLOCK(int, const struct icmp6_filter *); <netinet/icmp6.h> int ICMP6_FILTER_WILLPASS(int, const struct icmp6_filter *); draft-ietf-ipngwg-rfc2292bis-03.txt [Page 55]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 <netinet/in.h> int IN6_ARE_ADDR_EQUAL(const struct in6_addr *, const struct in6_addr *); <netinet/in.h> int inet6_opt_append(void *, size_t, int, uint8_t, size_t, uint_t, void **); <netinet/in.h> int inet6_opt_get_val(void *, size_t, void *, int); <netinet/in.h> int inet6_opt_find(void *, size_t, int, uint8_t , size_t *, void **); <netinet/in.h> int inet6_opt_finish(void *, size_t, int); <netinet/in.h> int inet6_opt_init(void *, size_t); <netinet/in.h> int inet6_opt_next(void *, size_t, int, uint8_t *, size_t *, void **); <netinet/in.h> int inet6_opt_set_val(void *, size_t, void *, int); <netinet/in.h> int inet6_rth_add(void *, const struct in6_addr *); <netinet/in.h> struct in6_addr inet6_rth_getaddr(const void *, int); <netinet/in.h> void *inet6_rth_init(void *, int, int, int); <netinet/in.h> int inet6_rth_reverse(const void *, void *); <netinet/in.h> int inet6_rth_segments(const void *); <netinet/in.h> size_t inet6_rth_space(int, int); <netinet/ip6.h> int IP6OPT_TYPE(uint8_t); <sys/socket.h> unsigned int CMSG_LEN(unsigned int); <sys/socket.h> unsigned int CMSG_SPACE(unsigned int); <unistd.h> int rresvport_af(int *, int); <unistd.h> int rcmd_af(char **, unsigned short, const char *, const char *, const char *, int *, int); <unistd.h> int rexec_af(char **, unsigned short , const char *, const char *, const char *, int *, int); 16. Security Considerations The setting of certain Hop-by-Hop options and Destination options may be restricted to privileged processes. Similarly some Hop-by-Hop options and Destination options may not be returned to nonprivileged applications. The ability to specify an arbitrary source address using IPV6_PKTINFO must be prevented; at least for non-privileged processes. The use of IPV6_REACHCONF ancillary data item may cause a denial of draft-ietf-ipngwg-rfc2292bis-03.txt [Page 56]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 service attack from a local application. 17. Change History Changes from RFC 2292: - Removed the IPV6_PKTOPTIONS socket option by allowing sticky options to be set with individual setsockopt calls. This simplifies the protocol stack implementation by not having to handle options within options and also clarifies the failure semantics when some option is incorrectly formatted. - Added the IPV6_RTHDRDSTOPTS for a Destination header before the Routing header. This is necessary to allow setting these Destination headers without IPV6_PKTOPTIONS. - Removed the ability to be able to specify Hop-by-Hop and Destination options using multiple ancillary data items. The application, using the inet6_option_*() routines, is responsible for formatting the whole extension header. This removes the need for the protocol stack to somehow guess the alignment restrictions on options when concatenating them together. - Added separate IPV6_RECVxxx options to enable the receipt of the corresponding ancillary data items. This makes the API cleaner since it allows the application to retrieve with getsockopt the sticky options it has set with setsockopt. - Clarified how sticky options are turned off. - Clarified how and when TCP returns ancillary data. - Removed the support for the loose/strict Routing header since that has been removed from the IPv6 specification. - Modified the inet6_rthdr_XXX() functions to not assume a cmsghdr structure in order to work with both sticky options and ancillary data. Renamed the functions to inet6_rth_XXX() to allow implementations to provide both the old and new functions. - Modified the inet6_option_XXX() functions to not assume a cmsghdr structure in order to work with both sticky options and ancillary data. Renamed the functions to inet6_opt_XXX() to allow implementations to provide both the old and new functions. - The new inet6_opt_XXX() functions were made different that the old as to not require structure declarations but instead use draft-ietf-ipngwg-rfc2292bis-03.txt [Page 57]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 functions to add the individual fields to the option. - Changed inet6_rthdr_getaddr() to operate on index O through N-1 (used to be 1 through N). - Changed the comments in the struct ip6_hdr from "priority" to "traffic class". - Clarified the alignment issues involving ancillary data to allow for separate alignment of cmsghdr structures and the data. Made CMSG_SPACE() return an upper bound on the needed space. - Added rcmd_af() and rexec_af(). Changes since -00: - Changed ICMP unreachable code 2 name to be "beyond scope of source address". - Added motivation for rcmd_af() and rexec_af(). - Added option definitions (IP6OPT_PAD1 etc) to ip6.h. - Added MLD and router renumbering definitions to icmp6.h - Removed ip6r0_addr field - replaced by a comment. - Made the content of IPV6_RTHDR, IPV6_HOPOPTS etc be specified as the extension header format (struct ip6_rthdr etc) instead of the previous "implementation dependent". - Removed attempt at RFC 2292 compatibility. - Excluded pad options from inet6_opt_next(). - Added IPV6_USE_MIN_MTU socket option for applications to avoid fragmentation by sending at the minimum IPv6 MTU. - Added MTU notification so that UDP and raw socket applications can participate in path MTU discovery. - Added Reachability confirmation for UDP and raw socket applications. - Clarified that if the application asks for e.g., IPV6_RTHDR and a received datagram does not contain a Routing header an implementation will exclude the IPV6_RTHDR ancillary data item. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 58]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 - Removed the constraints for jumbo option. - Moved the new CMSG macros and changes from the appendix. - Add text about inet6_opt_ depending on 2460 appendix B formatting rules i.e. largest field last in the option. - Specified that getsockopt() of a sticky option returns what was set with setsockopt(). - Updated the summary of new definitions to make it current. Changes since -01: - Added a note about the minor threat for DoS attacks using IPV6_REACHCONF - Clarified checksum and other receive side verification for RAW ICMP sockets. - Editorial clarifications. Changes since -02: - Changed IPV6_PATHMTU to carry a ip6_mtuinfo data structure. - Added the ability to do a getsockopt with IPV6_PATHMTU. - Added IPV6_DONTFRAG socket option. - Incorporated IPV6_TCLASS and friends, from draft-itojun-ipv6- tclass-api-03.txt. - Removed definitions and descriptions about ongoing stuff, including ones for mobile IPv6 and site prefixes. - Revised the overriding mechanism of sticky options so that a sticky option can only be overridden by an ancillary data item of the same option name. - Loosened requirements on the size of option fields in inet6_opt_get_val() and inet6_opt_set_val(). - Added credits for the original idea of IPV6_USE_MIN_MTU. - Clarified how to clear sticky options and the ICMPv6 filter. - Clarified alignment issues on inet6_opt_set_val(). draft-ietf-ipngwg-rfc2292bis-03.txt [Page 59]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 - Clarified that IPV6_CHECKSUM assumes an even positive offset and that the checksum field is aligned on a 16-bit boundary. - Removed the ip6_ext structure, which was intended to be used as a "generic" extension header prototype. But the working group consensus was that we should NOT include such stuff. - Revised the "TCP implications" section; for the receiving side, reverted to a RFC2292-style getsockopt instead of using recvmsg() and ancillary data. - Disabled the use of the IPV6_HOPLIMIT sticky option. - Clarified the ordering between IPV6_MULTICAST_IF and the IPV6_PKTINFO sticky option for mutlcast packets. - Added considerations on Specifying/Receiving Source/Destination Address, mainly about TCP implications. - Clarified the scoped-address case of the source address specification; the kernel must first determine the appropriate scope zone. - Added a summary about the interface selection rule. - Clarified that IPV6_NEXTHOP should be ignored for a multicast destination and that it should not contradict with the specified outgoing interface. - Added clarifications on exten headers ordering; for the sending side, assume the recommended ordering described in RFC2460. For the receiving side, do not assume any ordering and pass all headers to the application in the received order. - Clarified return values of getsockopt() for IPV6_xxx sticky options when no sticky option value has been set by setsockopt(). - Described TCP implications about "additional advanced API functions." - Updated text about Hop-by-Hop and Destination options headers that was based on the old RFC version of this API document. - Updated the URL for protocol numbers. - Clarified that access to the flow label field was not provided. - Removed IPV6_RECVRTHDRDSTOPTS. Since we have loosened the draft-ietf-ipngwg-rfc2292bis-03.txt [Page 60]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 ordering restriction for the receiving side, it is not meaningful to separate the two cases. - Clearly stated that this API only handles the case where IPV6_NEXTHOP takes sockaddr_in6. 18. Open Issues Open issues: - Do we really need to standardize rcmd functions here? - Is this a good idea to revive the IPV6_PKTOPTIONS option to get the optional information on a TCP socket? Or should we keep the previous usage using recvmsg() and ancillary data? The latter approach has a merit of less overhead and the ability to provide applications with more chances to follow changes on the optional information. However, it still does not provide complete information of the changes, and, thus, it cannot be used for security purposes (such as the filtering based on the receiving hop limit). Also, since the optional information always comes with a data segment, a TCP application that do not receive a data segment (i.e. an application only receiving SYN, FIN, and ACK- only segments) cannot get any optional information. Those issues are the reason for the specification change in this revision, but it may be controversial. 19. References [RFC-2460] Deering, S., Hinden, R., "Internet Protocol, Version 6 (IPv6), Specification", RFC 2460, Dec. 1998. [RFC-2553] Gilligan, R. E., Thomson, S., Bound, J., Stevens, W., "Basic Socket Interface Extensions for IPv6", RFC 2553, March 1999. [RFC-1981] McCann, J., Deering, S., Mogul, J, "Path MTU Discovery for IP version 6", RFC 1981, Aug. 1996. [RFC-2461] Narten, T., Nordmark, E., Simpson, W., "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, Dec. 1998. 20. Acknowledgments draft-ietf-ipngwg-rfc2292bis-03.txt [Page 61]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 Matt Thomas and Jim Bound have been working on the technical details in this draft for over a year. Keith Sklower is the original implementor of ancillary data in the BSD networking code. Craig Metz provided lots of feedback, suggestions, and comments based on his implementing many of these features as the document was being written. Mark Andrews first proposed the idea of the IPV6_USE_MIN_MTU option. Jun-ichiro Hagino contributed text for the traffic class API from a draft of his own. The following provided comments on earlier drafts: Pascal Anelli, Hamid Asayesh, Ran Atkinson, Karl Auerbach, Hamid Asayesh, Don Coolidge, Matt Crawford, Sam T. Denton, Richard Draves, Francis Dupont, Lilian Fernandes, Bob Gilligan, Gerri Harter, Tim Hartrick, Bob Halley, Masaki Hirabaru, Yoshinobu Inoue, Mukesh Kacker, A. N. Kuznetsov, Sam Manthorpe, Pedro Marques, Jack McCann, der Mouse, John Moy, Lori Napoli, Thomas Narten, Atsushi Onoe, Steve Parker, Charles Perkins, Ken Powell, Tom Pusateri, Pedro Roque, Sameer Shah, Peter Sjodin, Stephen P. Spackman, Jinmei Tatuya, Karen Tracey, Sowmini Varadhan, Quaizar Vohra, Carl Williams, Steve Wise, Eric Wong, Farrell Woods, Kazu Yamamoto, Vlad Yasevich, and YOSHIFUJI Hideaki. 21. Authors' Addresses W. Richard Stevens (deceased) Matt Thomas 3am Software Foundry 8053 Park Villa Circle Cupertino, CA 95014 Email: matt@3am-software.com Erik Nordmark Sun Microsystems Laboratories, Europe 29 Chemin du Vieux Chene 38240 Meylan, France Email: Erik.Nordmark@sun.com Tatuya JINMEI Corporate Research & Development Center, Toshiba Corporation 1 Komukai Toshiba-cho, Kawasaki-shi Kanagawa 212-8582, Japan Email: jinmei@isl.rdc.toshiba.co.jp draft-ietf-ipngwg-rfc2292bis-03.txt [Page 62]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 22. Appendix A: Ancillary Data Overview 4.2BSD allowed file descriptors to be transferred between separate processes across a UNIX domain socket using the sendmsg() and recvmsg() functions. Two members of the msghdr structure, msg_accrights and msg_accrightslen, were used to send and receive the descriptors. When the OSI protocols were added to 4.3BSD Reno in 1990 the names of these two fields in the msghdr structure were changed to msg_control and msg_controllen, because they were used by the OSI protocols for "control information", although the comments in the source code call this "ancillary data". Other than the OSI protocols, the use of ancillary data has been rare. In 4.4BSD, for example, the only use of ancillary data with IPv4 is to return the destination address of a received UDP datagram if the IP_RECVDSTADDR socket option is set. With Unix domain sockets ancillary data is still used to send and receive descriptors. Nevertheless the ancillary data fields of the msghdr structure provide a clean way to pass information in addition to the data that is being read or written. The inclusion of the msg_control and msg_controllen members of the msghdr structure along with the cmsghdr structure that is pointed to by the msg_control member is required by the Posix.1g sockets API standard. 22.1. The msghdr Structure The msghdr structure is used by the recvmsg() and sendmsg() functions. Its Posix.1g definition is: struct msghdr { void *msg_name; /* ptr to socket address structure */ socklen_t msg_namelen; /* size of socket address structure */ struct iovec *msg_iov; /* scatter/gather array */ size_t msg_iovlen; /* # elements in msg_iov */ void *msg_control; /* ancillary data */ socklen_t msg_controllen; /* ancillary data buffer length */ int msg_flags; /* flags on received message */ }; The structure is declared as a result of including <sys/socket.h>. (Note: Before Posix.1g the two "void *" pointers were typically "char *", and the two socklen_t members and the size_t member were typically integers. Earlier drafts of Posix.1g had the two socklen_t members as size_t, but Draft 6.6 of Posix.1g, apparently the final draft-ietf-ipngwg-rfc2292bis-03.txt [Page 63]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 draft, changed these to socklen_t to simplify binary portability for 64-bit implementations and to align Posix.1g with X/Open's Networking Services, Issue 5. The change in msg_control to a "void *" pointer affects any code that increments this pointer.) Most Berkeley-derived implementations limit the amount of ancillary data in a call to sendmsg() to no more than 108 bytes (an mbuf). This API requires a minimum of 10240 bytes of ancillary data, but it is recommended that the amount be limited only by the buffer space reserved by the socket (which can be modified by the SO_SNDBUF socket option). (Note: This magic number 10240 was picked as a value that should always be large enough. 108 bytes is clearly too small as the maximum size of a Routing header is 2048 bytes.) 22.2. The cmsghdr Structure The cmsghdr structure describes ancillary data objects transferred by recvmsg() and sendmsg(). Its Posix.1g definition is: struct cmsghdr { socklen_t cmsg_len; /* #bytes, including this header */ int cmsg_level; /* originating protocol */ int cmsg_type; /* protocol-specific type */ /* followed by unsigned char cmsg_data[]; */ }; This structure is declared as a result of including <sys/socket.h>. (Note: Before Posix.1g the cmsg_len member was an integer, and not a socklen_t. See the Note in the previous section for why socklen_t is used here.) As shown in this definition, normally there is no member with the name cmsg_data[]. Instead, the data portion is accessed using the CMSG_xxx() macros, as described in Section 22.3. Nevertheless, it is common to refer to the cmsg_data[] member. When ancillary data is sent or received, any number of ancillary data objects can be specified by the msg_control and msg_controllen members of the msghdr structure, because each object is preceded by a cmsghdr structure defining the object's length (the cmsg_len member). Historically Berkeley-derived implementations have passed only one object at a time, but this API allows multiple objects to be passed in a single call to sendmsg() or recvmsg(). The following example shows two ancillary data objects in a control buffer. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 64]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 |<--------------------------- msg_controllen -------------------------->| | OR | |<--------------------------- msg_controllen ----------------------->| | | |<----- ancillary data object ----->|<----- ancillary data object ----->| |<------ min CMSG_SPACE() --------->|<------ min CMSG_SPACE() --------->| | | | |<---------- cmsg_len ---------->| |<--------- cmsg_len ----------->| | |<--------- CMSG_LEN() --------->| |<-------- CMSG_LEN() ---------->| | | | | | | +-----+-----+-----+--+-----------+--+-----+-----+-----+--+-----------+--+ |cmsg_|cmsg_|cmsg_|XX| |XX|cmsg_|cmsg_|cmsg_|XX| |XX| |len |level|type |XX|cmsg_data[]|XX|len |level|type |XX|cmsg_data[]|XX| +-----+-----+-----+--+-----------+--+-----+-----+-----+--+-----------+--+ ^ | msg_control points here The fields shown as "XX" are possible padding, between the cmsghdr structure and the data, and between the data and the next cmsghdr structure, if required by the implementation. While sending an application may or may not include padding at the end of last ancillary data in msg_controllen and implementations must accept both as valid. On receiving a portable application must provide space for padding at the end of the last ancillary data as implementations may copy out the padding at the end of the control message buffer and include it in the received msg_controllen. When recvmsg() is called if msg_controllen is too small for all the ancillary data items including any trailing padding after the last item an implementation may set MSG_CTRUNC. 22.3. Ancillary Data Object Macros To aid in the manipulation of ancillary data objects, three macros from 4.4BSD are defined by Posix.1g: CMSG_DATA(), CMSG_NXTHDR(), and CMSG_FIRSTHDR(). Before describing these macros, we show the following example of how they might be used with a call to recvmsg(). draft-ietf-ipngwg-rfc2292bis-03.txt [Page 65]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 struct msghdr msg; struct cmsghdr *cmsgptr; /* fill in msg */ /* call recvmsg() */ for (cmsgptr = CMSG_FIRSTHDR(&msg); cmsgptr != NULL; cmsgptr = CMSG_NXTHDR(&msg, cmsgptr)) { if (cmsgptr->cmsg_len == 0) { /* Error handling */ break; } if (cmsgptr->cmsg_level == ... && cmsgptr->cmsg_type == ... ) { u_char *ptr; ptr = CMSG_DATA(cmsgptr); /* process data pointed to by ptr */ } } We now describe the three Posix.1g macros, followed by two more that are new with this API: CMSG_SPACE() and CMSG_LEN(). All these macros are defined as a result of including <sys/socket.h>. 22.3.1. CMSG_FIRSTHDR struct cmsghdr *CMSG_FIRSTHDR(const struct msghdr *mhdr); CMSG_FIRSTHDR() returns a pointer to the first cmsghdr structure in the msghdr structure pointed to by mhdr. The macro returns NULL if there is no ancillary data pointed to by the msghdr structure (that is, if either msg_control is NULL or if msg_controllen is less than the size of a cmsghdr structure). One possible implementation could be #define CMSG_FIRSTHDR(mhdr) \ ( (mhdr)->msg_controllen >= sizeof(struct cmsghdr) ? \ (struct cmsghdr *)(mhdr)->msg_control : \ (struct cmsghdr *)NULL ) (Note: Most existing implementations do not test the value of msg_controllen, and just return the value of msg_control. The value of msg_controllen must be tested, because if the application asks draft-ietf-ipngwg-rfc2292bis-03.txt [Page 66]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 recvmsg() to return ancillary data, by setting msg_control to point to the application's buffer and setting msg_controllen to the length of this buffer, the kernel indicates that no ancillary data is available by setting msg_controllen to 0 on return. It is also easier to put this test into this macro, than making the application perform the test.) 22.3.2. CMSG_NXTHDR struct cmsghdr *CMSG_NXTHDR(const struct msghdr *mhdr, const struct cmsghdr *cmsg); CMSG_NXTHDR() returns a pointer to the cmsghdr structure describing the next ancillary data object. mhdr is a pointer to a msghdr structure and cmsg is a pointer to a cmsghdr structure. If there is not another ancillary data object, the return value is NULL. The following behavior of this macro is new to this API: if the value of the cmsg pointer is NULL, a pointer to the cmsghdr structure describing the first ancillary data object is returned. That is, CMSG_NXTHDR(mhdr, NULL) is equivalent to CMSG_FIRSTHDR(mhdr). If there are no ancillary data objects, the return value is NULL. This provides an alternative way of coding the processing loop shown earlier: struct msghdr msg; struct cmsghdr *cmsgptr = NULL; /* fill in msg */ /* call recvmsg() */ while ((cmsgptr = CMSG_NXTHDR(&msg, cmsgptr)) != NULL) { if (cmsgptr->cmsg_len == 0) { /* Error handling */ break; } if (cmsgptr->cmsg_level == ... && cmsgptr->cmsg_type == ... ) { u_char *ptr; ptr = CMSG_DATA(cmsgptr); /* process data pointed to by ptr */ } } draft-ietf-ipngwg-rfc2292bis-03.txt [Page 67]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 One possible implementation could be: #define CMSG_NXTHDR(mhdr, cmsg) \ (((cmsg) == NULL) ? CMSG_FIRSTHDR(mhdr) : \ (((u_char *)(cmsg) + ALIGN_H((cmsg)->cmsg_len) \ + ALIGN_D(sizeof(struct cmsghdr)) > \ (u_char *)((mhdr)->msg_control) + (mhdr)->msg_controllen) ? \ (struct cmsghdr *)NULL : \ (struct cmsghdr *)((u_char *)(cmsg) + ALIGN_H((cmsg)->cmsg_len)))) The macros ALIGN_H() and ALIGN_D(), which are implementation dependent, round their arguments up to the next even multiple of whatever alignment is required for the start of the cmsghdr structure and the data, respectively. (This is probably a multiple of 4 or 8 bytes.) They are often the same macro in implementations platforms where alignment requirement for header and data is chosen to be identical. 22.3.3. CMSG_DATA unsigned char *CMSG_DATA(const struct cmsghdr *cmsg); CMSG_DATA() returns a pointer to the data (what is called the cmsg_data[] member, even though such a member is not defined in the structure) following a cmsghdr structure. One possible implementation could be: #define CMSG_DATA(cmsg) ( (u_char *)(cmsg) + \ ALIGN_D(sizeof(struct cmsghdr)) ) 22.3.4. CMSG_SPACE unsigned int CMSG_SPACE(unsigned int length); This macro is new with this API. Given the length of an ancillary data object, CMSG_SPACE() returns an upper bound on the space required by the object and its cmsghdr structure, including any padding needed to satisfy alignment requirements. This macro can be used, for example, when allocating space dynamically for the ancillary data. This macro should not be used to initialize the cmsg_len member of a cmsghdr structure; instead use the CMSG_LEN() macro. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 68]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 One possible implementation could be: #define CMSG_SPACE(length) ( ALIGN_D(sizeof(struct cmsghdr)) + \ ALIGN_H(length) ) 22.3.5. CMSG_LEN unsigned int CMSG_LEN(unsigned int length); This macro is new with this API. Given the length of an ancillary data object, CMSG_LEN() returns the value to store in the cmsg_len member of the cmsghdr structure, taking into account any padding needed to satisfy alignment requirements. One possible implementation could be: #define CMSG_LEN(length) ( ALIGN_D(sizeof(struct cmsghdr)) + length ) Note the difference between CMSG_SPACE() and CMSG_LEN(), shown also in the figure in Section 4.2: the former accounts for any required padding at the end of the ancillary data object and the latter is the actual length to store in the cmsg_len member of the ancillary data object. 23. Appendix B: Examples using the inet6_rth_XXX() functions Here we show an example for both sending Routing headers and processing and reversing a received Routing header. 23.1. Sending a Routing Header As an example of these Routing header functions defined in this document, we go through the function calls for the example on p. 17 of [RFC-2460]. The source is S, the destination is D, and the three intermediate nodes are I1, I2, and I3. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 69]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 S -----> I1 -----> I2 -----> I3 -----> D src: * S S S S S dst: D I1 I2 I3 D D A[1]: I1 I2 I1 I1 I1 I1 A[2]: I2 I3 I3 I2 I2 I2 A[3]: I3 D D D I3 I3 #seg: 3 3 2 1 0 3 src and dst are the source and destination IPv6 addresses in the IPv6 header. A[1], A[2], and A[3] are the three addresses in the Routing header. #seg is the Segments Left field in the Routing header. The six values in the column beneath node S are the values in the Routing header specified by the sending application using sendmsg() of setsockopt(). The function calls by the sender would look like: void *extptr; int extlen; struct msghdr msg; struct cmsghdr *cmsgptr; int cmsglen; struct sockaddr_in6 I1, I2, I3, D; extlen = inet6_rth_space(IPV6_RTHDR_TYPE_0, 3); cmsglen = CMSG_SPACE(extlen); cmsgptr = malloc(cmsglen); cmsgptr->cmsg_len = CMSG_LEN(extlen); cmsgptr->cmsg_level = IPPROTO_IPV6; cmsgptr->cmsg_type = IPV6_RTHDR; extptr = CMSG_DATA(cmsgptr); extptr = inet6_rth_init(extptr, extlen, IPV6_RTHDR_TYPE_0, 3); inet6_rth_add(extptr, &I1.sin6_addr); inet6_rth_add(extptr, &I2.sin6_addr); inet6_rth_add(extptr, &I3.sin6_addr); msg.msg_control = cmsgptr; msg.msg_controllen = cmsglen; /* finish filling in msg{}, msg_name = D */ /* call sendmsg() */ We also assume that the source address for the socket is not specified (i.e., the asterisk in the figure). draft-ietf-ipngwg-rfc2292bis-03.txt [Page 70]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 The four columns of six values that are then shown between the five nodes are the values of the fields in the packet while the packet is in transit between the two nodes. Notice that before the packet is sent by the source node S, the source address is chosen (replacing the asterisk), I1 becomes the destination address of the datagram, the two addresses A[2] and A[3] are "shifted up", and D is moved to A[3]. The columns of values that are shown beneath the destination node are the values returned by recvmsg(), assuming the application has enabled both the IPV6_RECVPKTINFO and IPV6_RECVRTHDR socket options. The source address is S (contained in the sockaddr_in6 structure pointed to by the msg_name member), the destination address is D (returned as an ancillary data object in an in6_pktinfo structure), and the ancillary data object specifying the Routing header will contain three addresses (I1, I2, and I3). The number of segments in the Routing header is known from the Hdr Ext Len field in the Routing header (a value of 6, indicating 3 addresses). The return value from inet6_rth_segments() will be 3 and inet6_rth_getaddr(0) will return I1, inet6_rth_getaddr(1) will return I2, and inet6_rth_getaddr(2) will return I3, If the receiving application then calls inet6_rth_reverse(), the order of the three addresses will become I3, I2, and I1. We can also show what an implementation might store in the ancillary data object as the Routing header is being built by the sending process. If we assume a 32-bit architecture where sizeof(struct cmsghdr) equals 12, with a desired alignment of 4-byte boundaries, then the call to inet6_rth_space(3) returns 68: 12 bytes for the cmsghdr structure and 56 bytes for the Routing header (8 + 3*16). The call to inet6_rth_init() initializes the ancillary data object to contain a Type 0 Routing header: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmsg_len = 20 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmsg_level = IPPROTO_IPV6 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmsg_type = IPV6_RTHDR | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len=6 | Routing Type=0| Seg Left=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ draft-ietf-ipngwg-rfc2292bis-03.txt [Page 71]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 The first call to inet6_rth_add() adds I1 to the list. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmsg_len = 36 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmsg_level = IPPROTO_IPV6 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmsg_type = IPV6_RTHDR | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len=6 | Routing Type=0| Seg Left=1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Address[1] = I1 + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ cmsg_len is incremented by 16, and the Segments Left field is incremented by 1. The next call to inet6_rth_add() adds I2 to the list. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 72]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmsg_len = 52 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmsg_level = IPPROTO_IPV6 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmsg_type = IPV6_RTHDR | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len=6 | Routing Type=0| Seg Left=2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Address[1] = I1 + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Address[2] = I2 + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ cmsg_len is incremented by 16, and the Segments Left field is incremented by 1. The last call to inet6_rth_add() adds I3 to the list. draft-ietf-ipngwg-rfc2292bis-03.txt [Page 73]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmsg_len = 68 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmsg_level = IPPROTO_IPV6 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmsg_type = IPV6_RTHDR | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len=6 | Routing Type=0| Seg Left=3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Address[1] = I1 + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Address[2] = I2 + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Address[3] = I3 + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ cmsg_len is incremented by 16, and the Segments Left field is incremented by 1. 23.2. Receiving Routing Headers This example assumes that the application has enabled IPV6_RECVRTHDR socket option. The application prints and reverses a source route and uses that to echo the received data. struct sockaddr_in6 addr; draft-ietf-ipngwg-rfc2292bis-03.txt [Page 74]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 struct msghdr msg; struct iovec iov; struct cmsghdr *cmsgptr; size_t cmsgspace; void *extptr; int extlen; int segments; int i; char databuf[8192]; segments = 100; /* Enough */ extlen = inet6_rth_space(IPV6_RTHDR_TYPE_0, segments); cmsgspace = CMSG_SPACE(extlen); cmsgptr = malloc(cmsgspace); if (cmsgptr == NULL) { perror("malloc"); exit(1); } extptr = CMSG_DATA(cmsgptr); msg.msg_control = (char *)cmsgptr; msg.msg_controllen = cmsgspace; msg.msg_name = (struct sockaddr *)&addr; msg.msg_namelen = sizeof (addr); msg.msg_iov = &iov; msg.msg_iovlen = 1; iov.iov_base = databuf; iov.iov_len = sizeof (databuf); msg.msg_flags = 0; if (recvmsg(s, &msg, 0) == -1) { perror("recvmsg"); return; } 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; rthdr = (struct ip6_rthdr *)extptr; segments = inet6_rth_segments(extptr); printf("route (%d segments, %d left): ", segments, rthdr->ip6r_segleft); for (i = 0; i < segments; i++) { in6 = inet6_rth_getaddr(extptr, i); if (in6 == NULL) draft-ietf-ipngwg-rfc2292bis-03.txt [Page 75]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 printf("<NULL> "); else printf("%s ", inet_ntop(AF_INET6, (void *)in6->s6_addr, asciiname, INET6_ADDRSTRLEN)); } if (inet6_rth_reverse(extptr, extptr) == -1) { printf("reverse failed"); return; } } iov.iov_base = databuf; iov.iov_len = strlen(databuf); if (sendmsg(s, &msg, 0) == -1) perror("sendmsg"); if (cmsgptr != NULL) free(cmsgptr); Note: The above example is a simple illustration. It skips some error checks involving the MSG_TRUNC and MSG_CTRUNC flags. 24. Appendix C: Examples using the inet6_opt_XXX() functions This shows how Hop-by-Hop and Destination options can be both built as well as parsed using the inet6_opt_XXX() functions. This examples assume that there are defined values for OPT_X and OPT_Y. 24.1. Building options We now provide an example that builds two Hop-by-Hop options using the example in Appendix B of [RFC-2460]. void *extbuf; size_t extlen; int currentlen; void *databuf; size_t offset; uint8_t value1; uint16_t value2; uint32_t value4; uint64_t value8; /* Estimate the length */ currentlen = inet6_opt_init(NULL, 0); if (currentlen == -1) return (-1); draft-ietf-ipngwg-rfc2292bis-03.txt [Page 76]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 currentlen = inet6_opt_append(NULL, 0, currentlen, OPT_X, 12, 8, NULL); if (currentlen == -1) return (-1); currentlen = inet6_opt_append(NULL, 0, currentlen, OPT_Y, 7, 4, NULL); if (currentlen == -1) return (-1); currentlen = inet6_opt_finish(NULL, 0, currentlen); if (currentlen == -1) return (-1); extlen = currentlen; extbuf = malloc(extlen); if (extbuf == NULL) { perror("malloc"); return (-1); } currentlen = inet6_opt_init(extbuf, extlen); if (currentlen == -1) return (-1); currentlen = inet6_opt_append(extbuf, extlen, currentlen, OPT_X, 12, 8, &databuf); if (currentlen == -1) return (-1); /* Insert value 0x12345678 for 4-octet field */ offset = 0; value4 = 0x12345678; offset = inet6_opt_set_val(databuf, offset, &value4, sizeof (value4)); /* Insert value 0x0102030405060708 for 8-octet field */ value8 = 0x0102030405060708; offset = inet6_opt_set_val(databuf, offset, &value8, sizeof (value8)); currentlen = inet6_opt_append(extbuf, extlen, currentlen, OPT_Y, 7, 4, &databuf); if (currentlen == -1) return (-1); /* Insert value 0x01 for 1-octet field */ offset = 0; value1 = 0x01; offset = inet6_opt_set_val(databuf, offset, &value1, sizeof (value1)); /* Insert value 0x1331 for 2-octet field */ value2 = 0x1331; offset = inet6_opt_set_val(databuf, offset, &value2, sizeof (value2)); /* Insert value 0x01020304 for 4-octet field */ value4 = 0x01020304; offset = inet6_opt_set_val(databuf, offset, &value4, sizeof (value4)); currentlen = inet6_opt_finish(extbuf, extlen, currentlen); draft-ietf-ipngwg-rfc2292bis-03.txt [Page 77]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 if (currentlen == -1) return (-1); /* extbuf and extlen are now completely formatted */ 24.2. Parsing received options This example parses and prints the content of the two options in the previous example. int print_opt(void *extbuf, size_t extlen) { struct ip6_dest *ext; int currentlen; uint8_t type; size_t len; void *databuf; size_t offset; uint8_t value1; uint16_t value2; uint32_t value4; uint64_t value8; ext = (struct ip6_dest *)extbuf; printf("nxt %u, len %u (bytes %d)\n", ext->ip6d_nxt, ext->ip6d_len, (ext->ip6d_len + 1) * 8); currentlen = 0; while (1) { currentlen = inet6_opt_next(extbuf, extlen, currentlen, &type, &len, &databuf); if (currentlen == -1) break; printf("Received opt %u len %u\n", type, len); switch (type) { case OPT_X: offset = 0; offset = inet6_opt_get_val(databuf, offset, &value4, sizeof (value4)); printf("X 4-byte field %x\n", value4); offset = inet6_opt_get_val(databuf, offset, &value8, sizeof (value8)); printf("X 8-byte field %llx\n", value8); break; case OPT_Y: draft-ietf-ipngwg-rfc2292bis-03.txt [Page 78]
INTERNET-DRAFT Advanced Sockets API for IPv6 Nov. 21, 2001 offset = 0; offset = inet6_opt_get_val(databuf, offset, &value1, sizeof (value1)); printf("Y 1-byte field %x\n", value1); offset = inet6_opt_get_val(databuf, offset, &value2, sizeof (value2)); printf("Y 2-byte field %x\n", value2); offset = inet6_opt_get_val(databuf, offset, &value4, sizeof (value4)); printf("Y 4-byte field %x\n", value4); break; default: printf("Unknown option %u\n", type); break; } } return (0); } draft-ietf-ipngwg-rfc2292bis-03.txt [Page 79]
