1.\" $KAME: ip6.4,v 1.23 2005/01/11 05:56:25 itojun Exp $ 2.\" $OpenBSD: ip6.4,v 1.21 2005/01/06 03:50:46 itojun Exp $ 3.\" 4.\" Copyright (c) 1983, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" $FreeBSD$ 32.\" 33.Dd March 13, 2011 34.Dt IP6 4 35.Os 36.Sh NAME 37.Nm ip6 38.Nd Internet Protocol version 6 (IPv6) network layer 39.Sh SYNOPSIS 40.In sys/socket.h 41.In netinet/in.h 42.Ft int 43.Fn socket AF_INET6 SOCK_RAW proto 44.Sh DESCRIPTION 45The IPv6 network layer is used by the IPv6 protocol family for 46transporting data. 47IPv6 packets contain an IPv6 header that is not provided as part of the 48payload contents when passed to an application. 49IPv6 header options affect the behavior of this protocol and may be used 50by high-level protocols (such as the 51.Xr tcp 4 52and 53.Xr udp 4 54protocols) as well as directly by 55.Dq raw sockets , 56which process IPv6 messages at a lower-level and may be useful for 57developing new protocols and special-purpose applications. 58.Ss Header 59All IPv6 packets begin with an IPv6 header. 60When data received by the kernel are passed to the application, this 61header is not included in buffer, even when raw sockets are being used. 62Likewise, when data are sent to the kernel for transmit from the 63application, the buffer is not examined for an IPv6 header: 64the kernel always constructs the header. 65To directly access IPv6 headers from received packets and specify them 66as part of the buffer passed to the kernel, link-level access 67.Po 68.Xr bpf 4 , 69for example 70.Pc 71must instead be utilized. 72.Pp 73The header has the following definition: 74.Bd -literal -offset indent 75struct ip6_hdr { 76 union { 77 struct ip6_hdrctl { 78 uint32_t ip6_un1_flow; /* 20 bits of flow ID */ 79 uint16_t ip6_un1_plen; /* payload length */ 80 uint8_t ip6_un1_nxt; /* next header */ 81 uint8_t ip6_un1_hlim; /* hop limit */ 82 } ip6_un1; 83 uint8_t ip6_un2_vfc; /* version and class */ 84 } ip6_ctlun; 85 struct in6_addr ip6_src; /* source address */ 86 struct in6_addr ip6_dst; /* destination address */ 87} __packed; 88 89#define ip6_vfc ip6_ctlun.ip6_un2_vfc 90#define ip6_flow ip6_ctlun.ip6_un1.ip6_un1_flow 91#define ip6_plen ip6_ctlun.ip6_un1.ip6_un1_plen 92#define ip6_nxt ip6_ctlun.ip6_un1.ip6_un1_nxt 93#define ip6_hlim ip6_ctlun.ip6_un1.ip6_un1_hlim 94#define ip6_hops ip6_ctlun.ip6_un1.ip6_un1_hlim 95.Ed 96.Pp 97All fields are in network-byte order. 98Any options specified (see 99.Sx Options 100below) must also be specified in network-byte order. 101.Pp 102.Va ip6_flow 103specifies the flow ID. 104.Va ip6_plen 105specifies the payload length. 106.Va ip6_nxt 107specifies the type of the next header. 108.Va ip6_hlim 109specifies the hop limit. 110.Pp 111The top 4 bits of 112.Va ip6_vfc 113specify the class and the bottom 4 bits specify the version. 114.Pp 115.Va ip6_src 116and 117.Va ip6_dst 118specify the source and destination addresses. 119.Pp 120The IPv6 header may be followed by any number of extension headers that start 121with the following generic definition: 122.Bd -literal -offset indent 123struct ip6_ext { 124 uint8_t ip6e_nxt; 125 uint8_t ip6e_len; 126} __packed; 127.Ed 128.Ss Options 129IPv6 allows header options on packets to manipulate the behavior of the 130protocol. 131These options and other control requests are accessed with the 132.Xr getsockopt 2 133and 134.Xr setsockopt 2 135system calls at level 136.Dv IPPROTO_IPV6 137and by using ancillary data in 138.Xr recvmsg 2 139and 140.Xr sendmsg 2 . 141They can be used to access most of the fields in the IPv6 header and 142extension headers. 143.Pp 144The following socket options are supported: 145.Bl -tag -width Ds 146.\" .It Dv IPV6_OPTIONS 147.It Dv IPV6_UNICAST_HOPS Fa "int *" 148Get or set the default hop limit header field for outgoing unicast 149datagrams sent on this socket. 150.\" .It Dv IPV6_RECVOPTS Fa "int *" 151.\" Get or set the status of whether all header options will be 152.\" delivered along with the datagram when it is received. 153.\" .It Dv IPV6_RECVRETOPTS Fa "int *" 154.\" Get or set the status of whether header options will be delivered 155.\" for reply. 156.\" .It Dv IPV6_RECVDSTADDR Fa "int *" 157.\" Get or set the status of whether datagrams are received with 158.\" destination addresses. 159.\" .It Dv IPV6_ORIGDSTADDR Fa "int *" 160.\" Get or set the status of whether datagrams are received with 161.\" destination addresses and destination ports. 162.\" .It Dv IPV6_RETOPTS 163.\" Get or set IPv6 options. 164.It Dv IPV6_MULTICAST_IF Fa "u_int *" 165Get or set the interface from which multicast packets will be sent. 166For hosts with multiple interfaces, each multicast transmission is sent 167from the primary network interface. 168The interface is specified as its index as provided by 169.Xr if_nametoindex 3 . 170A value of zero specifies the default interface. 171.It Dv IPV6_MULTICAST_HOPS Fa "int *" 172Get or set the default hop limit header field for outgoing multicast 173datagrams sent on this socket. 174This option controls the scope of multicast datagram transmissions. 175.Pp 176Datagrams with a hop limit of 1 are not forwarded beyond the local 177network. 178Multicast datagrams with a hop limit of zero will not be transmitted on 179any network but may be delivered locally if the sending host belongs to 180the destination group and if multicast loopback (see below) has not been 181disabled on the sending socket. 182Multicast datagrams with a hop limit greater than 1 may be forwarded to 183the other networks if a multicast router (such as 184.Xr mrouted 8 Pq Pa ports/net/mrouted ) 185is attached to the local network. 186.It Dv IPV6_MULTICAST_LOOP Fa "u_int *" 187Get or set the status of whether multicast datagrams will be looped back 188for local delivery when a multicast datagram is sent to a group to which 189the sending host belongs. 190.Pp 191This option improves performance for applications that may have no more 192than one instance on a single host (such as a router daemon) by 193eliminating the overhead of receiving their own transmissions. 194It should generally not be used by applications for which there may be 195more than one instance on a single host (such as a conferencing program) 196or for which the sender does not belong to the destination group 197(such as a time-querying program). 198.Pp 199A multicast datagram sent with an initial hop limit greater than 1 may 200be delivered to the sending host on a different interface from that on 201which it was sent if the host belongs to the destination group on that 202other interface. 203The multicast loopback control option has no effect on such delivery. 204.It Dv IPV6_JOIN_GROUP Fa "struct ipv6_mreq *" 205Join a multicast group. 206A host must become a member of a multicast group before it can receive 207datagrams sent to the group. 208.Bd -literal 209struct ipv6_mreq { 210 struct in6_addr ipv6mr_multiaddr; 211 unsigned int ipv6mr_interface; 212}; 213.Ed 214.Pp 215.Va ipv6mr_interface 216may be set to zeroes to choose the default multicast interface or to the 217index of a particular multicast-capable interface if the host is 218multihomed. 219Membership is associated with a single interface; programs running on 220multihomed hosts may need to join the same group on more than one 221interface. 222.Pp 223If the multicast address is unspecified (i.e., all zeroes), messages 224from all multicast addresses will be accepted by this group. 225Note that setting to this value requires superuser privileges. 226.It Dv IPV6_LEAVE_GROUP Fa "struct ipv6_mreq *" 227Drop membership from the associated multicast group. 228Memberships are automatically dropped when the socket is closed or when 229the process exits. 230.It Dv IPV6_PORTRANGE Fa "int *" 231Get or set the allocation policy of ephemeral ports for when the kernel 232automatically binds a local address to this socket. 233The following values are available: 234.Pp 235.Bl -tag -width IPV6_PORTRANGE_DEFAULT -compact 236.It Dv IPV6_PORTRANGE_DEFAULT 237Use the regular range of non-reserved ports (varies, see 238.Xr ip 4 ) . 239.It Dv IPV6_PORTRANGE_HIGH 240Use a high range (varies, see 241.Xr ip 4 ) . 242.It Dv IPV6_PORTRANGE_LOW 243Use a low, reserved range (600\-1023, see 244.Xr ip 4 ) . 245.El 246.It Dv IPV6_PKTINFO Fa "int *" 247Get or set whether additional information about subsequent packets will 248be provided as ancillary data along with the payload in subsequent 249.Xr recvmsg 2 250calls. 251The information is stored in the following structure in the ancillary 252data returned: 253.Bd -literal 254struct in6_pktinfo { 255 struct in6_addr ipi6_addr; /* src/dst IPv6 address */ 256 unsigned int ipi6_ifindex; /* send/recv if index */ 257}; 258.Ed 259.It Dv IPV6_HOPLIMIT Fa "int *" 260Get or set whether the hop limit header field from subsequent packets 261will be provided as ancillary data along with the payload in subsequent 262.Xr recvmsg 2 263calls. 264The value is stored as an 265.Vt int 266in the ancillary data returned. 267.\" .It Dv IPV6_NEXTHOP Fa "int *" 268.\" Get or set whether the address of the next hop for subsequent 269.\" packets will be provided as ancillary data along with the payload in 270.\" subsequent 271.\" .Xr recvmsg 2 272.\" calls. 273.\" The option is stored as a 274.\" .Vt sockaddr 275.\" structure in the ancillary data returned. 276.\" .Pp 277.\" This option requires superuser privileges. 278.It Dv IPV6_HOPOPTS Fa "int *" 279Get or set whether the hop-by-hop options from subsequent packets will be 280provided as ancillary data along with the payload in subsequent 281.Xr recvmsg 2 282calls. 283The option is stored in the following structure in the ancillary data 284returned: 285.Bd -literal 286struct ip6_hbh { 287 uint8_t ip6h_nxt; /* next header */ 288 uint8_t ip6h_len; /* length in units of 8 octets */ 289/* followed by options */ 290} __packed; 291.Ed 292.Pp 293The 294.Fn inet6_option_space 295routine and family of routines may be used to manipulate this data. 296.Pp 297This option requires superuser privileges. 298.It Dv IPV6_DSTOPTS Fa "int *" 299Get or set whether the destination options from subsequent packets will 300be provided as ancillary data along with the payload in subsequent 301.Xr recvmsg 2 302calls. 303The option is stored in the following structure in the ancillary data 304returned: 305.Bd -literal 306struct ip6_dest { 307 uint8_t ip6d_nxt; /* next header */ 308 uint8_t ip6d_len; /* length in units of 8 octets */ 309/* followed by options */ 310} __packed; 311.Ed 312.Pp 313The 314.Fn inet6_option_space 315routine and family of routines may be used to manipulate this data. 316.Pp 317This option requires superuser privileges. 318.It Dv IPV6_TCLASS Fa "int *" 319Get or set the value of the traffic class field used for outgoing datagrams 320on this socket. 321The value must be between \-1 and 255. 322A value of \-1 resets to the default value. 323.It Dv IPV6_RECVTCLASS Fa "int *" 324Get or set the status of whether the traffic class header field will be 325provided as ancillary data along with the payload in subsequent 326.Xr recvmsg 2 327calls. 328The header field is stored as a single value of type 329.Vt int . 330.It Dv IPV6_RTHDR Fa "int *" 331Get or set whether the routing header from subsequent packets will be 332provided as ancillary data along with the payload in subsequent 333.Xr recvmsg 2 334calls. 335The header is stored in the following structure in the ancillary data 336returned: 337.Bd -literal 338struct ip6_rthdr { 339 uint8_t ip6r_nxt; /* next header */ 340 uint8_t ip6r_len; /* length in units of 8 octets */ 341 uint8_t ip6r_type; /* routing type */ 342 uint8_t ip6r_segleft; /* segments left */ 343/* followed by routing-type-specific data */ 344} __packed; 345.Ed 346.Pp 347The 348.Fn inet6_option_space 349routine and family of routines may be used to manipulate this data. 350.Pp 351This option requires superuser privileges. 352.It Dv IPV6_PKTOPTIONS Fa "struct cmsghdr *" 353Get or set all header options and extension headers at one time on the 354last packet sent or received on the socket. 355All options must fit within the size of an mbuf (see 356.Xr mbuf 9 ) . 357Options are specified as a series of 358.Vt cmsghdr 359structures followed by corresponding values. 360.Va cmsg_level 361is set to 362.Dv IPPROTO_IPV6 , 363.Va cmsg_type 364to one of the other values in this list, and trailing data to the option 365value. 366When setting options, if the length 367.Va optlen 368to 369.Xr setsockopt 2 370is zero, all header options will be reset to their default values. 371Otherwise, the length should specify the size the series of control 372messages consumes. 373.Pp 374Instead of using 375.Xr sendmsg 2 376to specify option values, the ancillary data used in these calls that 377correspond to the desired header options may be directly specified as 378the control message in the series of control messages provided as the 379argument to 380.Xr setsockopt 2 . 381.It Dv IPV6_CHECKSUM Fa "int *" 382Get or set the byte offset into a packet where the 16-bit checksum is 383located. 384When set, this byte offset is where incoming packets will be expected 385to have checksums of their data stored and where outgoing packets will 386have checksums of their data computed and stored by the kernel. 387A value of \-1 specifies that no checksums will be checked on incoming 388packets and that no checksums will be computed or stored on outgoing 389packets. 390The offset of the checksum for ICMPv6 sockets cannot be relocated or 391turned off. 392.It Dv IPV6_V6ONLY Fa "int *" 393Get or set whether only IPv6 connections can be made to this socket. 394For wildcard sockets, this can restrict connections to IPv6 only. 395.\"With 396.\".Ox 397.\"IPv6 sockets are always IPv6-only, so the socket option is read-only 398.\"(not modifiable). 399.It Dv IPV6_USE_MIN_MTU Fa "int *" 400Get or set whether the minimal IPv6 maximum transmission unit (MTU) size 401will be used to avoid fragmentation from occurring for subsequent 402outgoing datagrams. 403.It Dv IPV6_AUTH_LEVEL Fa "int *" 404Get or set the 405.Xr ipsec 4 406authentication level. 407.It Dv IPV6_ESP_TRANS_LEVEL Fa "int *" 408Get or set the ESP transport level. 409.It Dv IPV6_ESP_NETWORK_LEVEL Fa "int *" 410Get or set the ESP encapsulation level. 411.It Dv IPV6_IPCOMP_LEVEL Fa "int *" 412Get or set the 413.Xr ipcomp 4 414level. 415.El 416.Pp 417The 418.Dv IPV6_PKTINFO , 419.\" .Dv IPV6_NEXTHOP , 420.Dv IPV6_HOPLIMIT , 421.Dv IPV6_HOPOPTS , 422.Dv IPV6_DSTOPTS , 423and 424.Dv IPV6_RTHDR 425options will return ancillary data along with payload contents in subsequent 426.Xr recvmsg 2 427calls with 428.Va cmsg_level 429set to 430.Dv IPPROTO_IPV6 431and 432.Va cmsg_type 433set to respective option name value (e.g., 434.Dv IPV6_HOPTLIMIT ) . 435These options may also be used directly as ancillary 436.Va cmsg_type 437values in 438.Xr sendmsg 2 439to set options on the packet being transmitted by the call. 440The 441.Va cmsg_level 442value must be 443.Dv IPPROTO_IPV6 . 444For these options, the ancillary data object value format is the same 445as the value returned as explained for each when received with 446.Xr recvmsg 2 . 447.Pp 448Note that using 449.Xr sendmsg 2 450to specify options on particular packets works only on UDP and raw sockets. 451To manipulate header options for packets on TCP sockets, only the socket 452options may be used. 453.Pp 454In some cases, there are multiple APIs defined for manipulating an IPv6 455header field. 456A good example is the outgoing interface for multicast datagrams, which 457can be set by the 458.Dv IPV6_MULTICAST_IF 459socket option, through the 460.Dv IPV6_PKTINFO 461option, and through the 462.Va sin6_scope_id 463field of the socket address passed to the 464.Xr sendto 2 465system call. 466.Pp 467Resolving these conflicts is implementation dependent. 468This implementation determines the value in the following way: 469options specified by using ancillary data (i.e., 470.Xr sendmsg 2 ) 471are considered first, 472options specified by using 473.Dv IPV6_PKTOPTIONS 474to set 475.Dq sticky 476options are considered second, 477options specified by using the individual, basic, and direct socket 478options (e.g., 479.Dv IPV6_UNICAST_HOPS ) 480are considered third, 481and options specified in the socket address supplied to 482.Xr sendto 2 483are the last choice. 484.Ss Multicasting 485IPv6 multicasting is supported only on 486.Dv AF_INET6 487sockets of type 488.Dv SOCK_DGRAM 489and 490.Dv SOCK_RAW , 491and only on networks where the interface driver supports 492multicasting. 493Socket options (see above) that manipulate membership of 494multicast groups and other multicast options include 495.Dv IPV6_MULTICAST_IF , 496.Dv IPV6_MULTICAST_HOPS , 497.Dv IPV6_MULTICAST_LOOP , 498.Dv IPV6_LEAVE_GROUP , 499and 500.Dv IPV6_JOIN_GROUP . 501.Ss Raw Sockets 502Raw IPv6 sockets are connectionless and are normally used with the 503.Xr sendto 2 504and 505.Xr recvfrom 2 506calls, although the 507.Xr connect 2 508call may be used to fix the destination address for future outgoing 509packets so that 510.Xr send 2 511may instead be used and the 512.Xr bind 2 513call may be used to fix the source address for future outgoing 514packets instead of having the kernel choose a source address. 515.Pp 516By using 517.Xr connect 2 518or 519.Xr bind 2 , 520raw socket input is constrained to only packets with their 521source address matching the socket destination address if 522.Xr connect 2 523was used and to packets with their destination address 524matching the socket source address if 525.Xr bind 2 526was used. 527.Pp 528If the 529.Ar proto 530argument to 531.Xr socket 2 532is zero, the default protocol 533.Pq Dv IPPROTO_RAW 534is used for outgoing packets. 535For incoming packets, protocols recognized by kernel are 536.Sy not 537passed to the application socket (e.g., 538.Xr tcp 4 539and 540.Xr udp 4 ) 541except for some ICMPv6 messages. 542The ICMPv6 messages not passed to raw sockets include echo, timestamp, 543and address mask requests. 544If 545.Ar proto 546is non-zero, only packets with this protocol will be passed to the 547socket. 548.Pp 549IPv6 fragments are also not passed to application sockets until 550they have been reassembled. 551If reception of all packets is desired, link-level access (such as 552.Xr bpf 4 ) 553must be used instead. 554.Pp 555Outgoing packets automatically have an IPv6 header prepended to them 556(based on the destination address and the protocol number the socket 557was created with). 558Incoming packets are received by an application without the IPv6 header 559or any extension headers. 560.Pp 561Outgoing packets will be fragmented automatically by the kernel if they 562are too large. 563Incoming packets will be reassembled before being sent to the raw socket, 564so packet fragments or fragment headers will never be seen on a raw socket. 565.Sh EXAMPLES 566The following determines the hop limit on the next packet received: 567.Bd -literal 568struct iovec iov[2]; 569u_char buf[BUFSIZ]; 570struct cmsghdr *cm; 571struct msghdr m; 572int optval; 573bool found; 574u_char data[2048]; 575 576/* Create socket. */ 577 578(void)memset(&m, 0, sizeof(m)); 579(void)memset(&iov, 0, sizeof(iov)); 580 581iov[0].iov_base = data; /* buffer for packet payload */ 582iov[0].iov_len = sizeof(data); /* expected packet length */ 583 584m.msg_name = &from; /* sockaddr_in6 of peer */ 585m.msg_namelen = sizeof(from); 586m.msg_iov = iov; 587m.msg_iovlen = 1; 588m.msg_control = (caddr_t)buf; /* buffer for control messages */ 589m.msg_controllen = sizeof(buf); 590 591/* 592 * Enable the hop limit value from received packets to be 593 * returned along with the payload. 594 */ 595optval = 1; 596if (setsockopt(s, IPPROTO_IPV6, IPV6_HOPLIMIT, &optval, 597 sizeof(optval)) == -1) 598 err(1, "setsockopt"); 599 600found = false; 601do { 602 if (recvmsg(s, &m, 0) == -1) 603 err(1, "recvmsg"); 604 for (cm = CMSG_FIRSTHDR(&m); cm != NULL; 605 cm = CMSG_NXTHDR(&m, cm)) { 606 if (cm->cmsg_level == IPPROTO_IPV6 && 607 cm->cmsg_type == IPV6_HOPLIMIT && 608 cm->cmsg_len == CMSG_LEN(sizeof(int))) { 609 found = true; 610 (void)printf("hop limit: %d\en", 611 *(int *)CMSG_DATA(cm)); 612 break; 613 } 614 } 615} while (!found); 616.Ed 617.Sh DIAGNOSTICS 618A socket operation may fail with one of the following errors returned: 619.Bl -tag -width EADDRNOTAVAILxx 620.It Bq Er EISCONN 621when trying to establish a connection on a socket which 622already has one or when trying to send a datagram with the destination 623address specified and the socket is already connected. 624.It Bq Er ENOTCONN 625when trying to send a datagram, but 626no destination address is specified, and the socket has not been 627connected. 628.It Bq Er ENOBUFS 629when the system runs out of memory for 630an internal data structure. 631.It Bq Er EADDRNOTAVAIL 632when an attempt is made to create a 633socket with a network address for which no network interface 634exists. 635.It Bq Er EACCES 636when an attempt is made to create 637a raw IPv6 socket by a non-privileged process. 638.El 639.Pp 640The following errors specific to IPv6 may occur when setting or getting 641header options: 642.Bl -tag -width EADDRNOTAVAILxx 643.It Bq Er EINVAL 644An unknown socket option name was given. 645.It Bq Er EINVAL 646An ancillary data object was improperly formed. 647.El 648.Sh SEE ALSO 649.Xr getsockopt 2 , 650.Xr recv 2 , 651.Xr send 2 , 652.Xr setsockopt 2 , 653.Xr socket 2 , 654.\" .Xr inet6_option_space 3 , 655.\" .Xr inet6_rthdr_space 3 , 656.Xr if_nametoindex 3 , 657.Xr bpf 4 , 658.Xr icmp6 4 , 659.Xr inet6 4 , 660.Xr ip 4 , 661.Xr netintro 4 , 662.Xr tcp 4 , 663.Xr udp 4 664.Rs 665.%A W. Stevens 666.%A M. Thomas 667.%T Advanced Sockets API for IPv6 668.%R RFC 2292 669.%D February 1998 670.Re 671.Rs 672.%A S. Deering 673.%A R. Hinden 674.%T Internet Protocol, Version 6 (IPv6) Specification 675.%R RFC 2460 676.%D December 1998 677.Re 678.Rs 679.%A R. Gilligan 680.%A S. Thomson 681.%A J. Bound 682.%A W. Stevens 683.%T Basic Socket Interface Extensions for IPv6 684.%R RFC 2553 685.%D March 1999 686.Re 687.Rs 688.%A W. Stevens 689.%A B. Fenner 690.%A A. Rudoff 691.%T UNIX Network Programming, third edition 692.Re 693.Sh STANDARDS 694Most of the socket options are defined in RFC 2292 or RFC 2553. 695The 696.Dv IPV6_V6ONLY 697socket option is defined in RFC 3493 Section 5.3. 698The 699.Dv IPV6_PORTRANGE 700socket option and the conflict resolution rule are not defined in the 701RFCs and should be considered implementation dependent. 702