1.\" $OpenBSD: ip6.4,v 1.25 2011/09/08 16:43:56 giovanni Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.Dd $Mdocdate: September 8 2011 $ 30.Dt IP6 4 31.Os 32.Sh NAME 33.Nm ip6 34.Nd Internet Protocol version 6 (IPv6) network layer 35.Sh SYNOPSIS 36.In sys/types.h 37.In sys/socket.h 38.In netinet/in.h 39.Ft int 40.Fn socket AF_INET6 SOCK_RAW proto 41.Sh DESCRIPTION 42The IPv6 network layer is used by the IPv6 protocol family for 43transporting data. 44IPv6 packets contain an IPv6 header that is not provided as part of the 45payload contents when passed to an application. 46IPv6 header options affect the behavior of this protocol and may be used 47by high-level protocols (such as the 48.Xr tcp 4 49and 50.Xr udp 4 51protocols) as well as directly by 52.Dq raw sockets , 53which process IPv6 messages at a lower-level and may be useful for 54developing new protocols and special-purpose applications. 55.Ss Header 56All IPv6 packets begin with an IPv6 header. 57When data received by the kernel are passed to the application, this 58header is not included in buffer, even when raw sockets are being used. 59Likewise, when data are sent to the kernel for transmit from the 60application, the buffer is not examined for an IPv6 header: 61the kernel always constructs the header. 62To directly access IPv6 headers from received packets and specify them 63as part of the buffer passed to the kernel, link-level access 64.Po 65.Xr bpf 4 , 66for example 67.Pc 68must instead be utilized. 69.Pp 70The header has the following definition: 71.Bd -literal -offset indent 72struct ip6_hdr { 73 union { 74 struct ip6_hdrctl { 75 u_int32_t ip6_un1_flow; /* 20 bits of flow ID */ 76 u_int16_t ip6_un1_plen; /* payload length */ 77 u_int8_t ip6_un1_nxt; /* next header */ 78 u_int8_t ip6_un1_hlim; /* hop limit */ 79 } ip6_un1; 80 u_int8_t ip6_un2_vfc; /* version and class */ 81 } ip6_ctlun; 82 struct in6_addr ip6_src; /* source address */ 83 struct in6_addr ip6_dst; /* destination address */ 84} __packed; 85 86#define ip6_vfc ip6_ctlun.ip6_un2_vfc 87#define ip6_flow ip6_ctlun.ip6_un1.ip6_un1_flow 88#define ip6_plen ip6_ctlun.ip6_un1.ip6_un1_plen 89#define ip6_nxt ip6_ctlun.ip6_un1.ip6_un1_nxt 90#define ip6_hlim ip6_ctlun.ip6_un1.ip6_un1_hlim 91#define ip6_hops ip6_ctlun.ip6_un1.ip6_un1_hlim 92.Ed 93.Pp 94All fields are in network-byte order. 95Any options specified (see 96.Sx Options 97below) must also be specified in network-byte order. 98.Pp 99.Va ip6_flow 100specifies the flow ID. 101.Va ip6_plen 102specifies the payload length. 103.Va ip6_nxt 104specifies the type of the next header. 105.Va ip6_hlim 106specifies the hop limit. 107.Pp 108The top 4 bits of 109.Va ip6_vfc 110specify the class and the bottom 4 bits specify the version. 111.Pp 112.Va ip6_src 113and 114.Va ip6_dst 115specify the source and destination addresses. 116.Pp 117The IPv6 header may be followed by any number of extension headers that start 118with the following generic definition: 119.Bd -literal -offset indent 120struct ip6_ext { 121 u_int8_t ip6e_nxt; 122 u_int8_t ip6e_len; 123} __packed; 124.Ed 125.Ss Options 126IPv6 allows header options on packets to manipulate the behavior of the 127protocol. 128These options and other control requests are accessed with the 129.Xr getsockopt 2 130and 131.Xr setsockopt 2 132system calls at level 133.Dv IPPROTO_IPV6 134and by using ancillary data in 135.Xr recvmsg 2 136and 137.Xr sendmsg 2 . 138They can be used to access most of the fields in the IPv6 header and 139extension headers. 140.Pp 141The following socket options are supported: 142.Bl -tag -width Ds 143.\" .It Dv IPV6_OPTIONS 144.It Dv IPV6_UNICAST_HOPS Fa "int *" 145Get or set the default hop limit header field for outgoing unicast 146datagrams sent on this socket. 147A value of \-1 resets to the default value. 148.\" .It Dv IPV6_RECVOPTS Fa "int *" 149.\" Get or set the status of whether all header options will be 150.\" delivered along with the datagram when it is received. 151.\" .It Dv IPV6_RECVRETOPTS Fa "int *" 152.\" Get or set the status of whether header options will be delivered 153.\" for reply. 154.\" .It Dv IPV6_RECVDSTADDR Fa "int *" 155.\" Get or set the status of whether datagrams are received with 156.\" destination addresses. 157.\" .It Dv IPV6_RETOPTS 158.\" Get or set IPv6 options. 159.It Dv IPV6_MULTICAST_IF Fa "u_int *" 160Get or set the interface from which multicast packets will be sent. 161For hosts with multiple interfaces, each multicast transmission is sent 162from the primary network interface. 163The interface is specified as its index as provided by 164.Xr if_nametoindex 3 . 165A value of zero specifies the default interface. 166.It Dv IPV6_MULTICAST_HOPS Fa "int *" 167Get or set the default hop limit header field for outgoing multicast 168datagrams sent on this socket. 169This option controls the scope of multicast datagram transmissions. 170.Pp 171Datagrams with a hop limit of 1 are not forwarded beyond the local 172network. 173Multicast datagrams with a hop limit of zero will not be transmitted on 174any network but may be delivered locally if the sending host belongs to 175the destination group and if multicast loopback (see below) has not been 176disabled on the sending socket. 177Multicast datagrams with a hop limit greater than 1 may be forwarded to 178the other networks if a multicast router (such as 179.Xr mrouted 8 ) 180is attached to the local network. 181.It Dv IPV6_MULTICAST_LOOP Fa "u_int *" 182Get or set the status of whether multicast datagrams will be looped back 183for local delivery when a multicast datagram is sent to a group to which 184the sending host belongs. 185.Pp 186This option improves performance for applications that may have no more 187than one instance on a single host (such as a router daemon) by 188eliminating the overhead of receiving their own transmissions. 189It should generally not be used by applications for which there may be 190more than one instance on a single host (such as a conferencing program) 191or for which the sender does not belong to the destination group 192(such as a time-querying program). 193.Pp 194A multicast datagram sent with an initial hop limit greater than 1 may 195be delivered to the sending host on a different interface from that on 196which it was sent if the host belongs to the destination group on that 197other interface. 198The multicast loopback control option has no effect on such delivery. 199.It Dv IPV6_JOIN_GROUP Fa "struct ipv6_mreq *" 200Join a multicast group. 201A host must become a member of a multicast group before it can receive 202datagrams sent to the group. 203.Bd -literal 204struct ipv6_mreq { 205 struct in6_addr ipv6mr_multiaddr; 206 unsigned int ipv6mr_interface; 207}; 208.Ed 209.Pp 210.Va ipv6mr_interface 211may be set to zeroes to choose the default multicast interface or to the 212index of a particular multicast-capable interface if the host is 213multihomed. 214Membership is associated with a single interface; programs running on 215multihomed hosts may need to join the same group on more than one 216interface. 217.Pp 218If the multicast address is unspecified (i.e., all zeroes), messages 219from all multicast addresses will be accepted by this group. 220Note that setting to this value requires superuser privileges. 221.It Dv IPV6_LEAVE_GROUP Fa "struct ipv6_mreq *" 222Drop membership from the associated multicast group. 223Memberships are automatically dropped when the socket is closed or when 224the process exits. 225.It Dv IPV6_PORTRANGE Fa "int *" 226Get or set the allocation policy of ephemeral ports for when the kernel 227automatically binds a local address to this socket. 228The following values are available: 229.Pp 230.Bl -tag -width IPV6_PORTRANGE_DEFAULT -compact 231.It Dv IPV6_PORTRANGE_DEFAULT 232Use the regular range of non-reserved ports (varies, see 233.Xr sysctl 8 ) . 234.It Dv IPV6_PORTRANGE_HIGH 235Use a high range (varies, see 236.Xr sysctl 8 ) . 237.It Dv IPV6_PORTRANGE_LOW 238Use a low, reserved range (600\-1023). 239.El 240.It Dv IPV6_PKTINFO Fa "int *" 241Get or set whether additional information about subsequent packets will 242be provided as ancillary data along with the payload in subsequent 243.Xr recvmsg 2 244calls. 245The information is stored in the following structure in the ancillary 246data returned: 247.Bd -literal 248struct in6_pktinfo { 249 struct in6_addr ipi6_addr; /* src/dst IPv6 address */ 250 unsigned int ipi6_ifindex; /* send/recv if index */ 251}; 252.Ed 253.It Dv IPV6_HOPLIMIT Fa "int *" 254Get or set whether the hop limit header field from subsequent packets 255will be provided as ancillary data along with the payload in subsequent 256.Xr recvmsg 2 257calls. 258The value is stored as an 259.Vt int 260in the ancillary data returned. 261.\" .It Dv IPV6_NEXTHOP Fa "int *" 262.\" Get or set whether the address of the next hop for subsequent 263.\" packets will be provided as ancillary data along with the payload in 264.\" subsequent 265.\" .Xr recvmsg 2 266.\" calls. 267.\" The option is stored as a 268.\" .Vt sockaddr 269.\" structure in the ancillary data returned. 270.\" .Pp 271.\" This option requires superuser privileges. 272.It Dv IPV6_HOPOPTS Fa "int *" 273Get or set whether the hop-by-hop options from subsequent packets will be 274provided as ancillary data along with the payload in subsequent 275.Xr recvmsg 2 276calls. 277The option is stored in the following structure in the ancillary data 278returned: 279.Bd -literal 280struct ip6_hbh { 281 u_int8_t ip6h_nxt; /* next header */ 282 u_int8_t ip6h_len; /* length in units of 8 octets */ 283/* followed by options */ 284} __packed; 285.Ed 286.Pp 287The 288.Fn inet6_option_space 289routine and family of routines may be used to manipulate this data. 290.Pp 291This option requires superuser privileges. 292.It Dv IPV6_DSTOPTS Fa "int *" 293Get or set whether the destination options from subsequent packets will 294be provided as ancillary data along with the payload in subsequent 295.Xr recvmsg 2 296calls. 297The option is stored in the following structure in the ancillary data 298returned: 299.Bd -literal 300struct ip6_dest { 301 u_int8_t ip6d_nxt; /* next header */ 302 u_int8_t ip6d_len; /* length in units of 8 octets */ 303/* followed by options */ 304} __packed; 305.Ed 306.Pp 307The 308.Fn inet6_option_space 309routine and family of routines may be used to manipulate this data. 310.Pp 311This option requires superuser privileges. 312.It Dv IPV6_TCLASS Fa "int *" 313Get or set the value of the traffic class field used for outgoing datagrams 314on this socket. 315The value must be between \-1 and 255. 316A value of \-1 resets to the default value. 317.It Dv IPV6_RECVTCLASS Fa "int *" 318Get or set the status of whether the traffic class header field will be 319provided as ancillary data along with the payload in subsequent 320.Xr recvmsg 2 321calls. 322The header field is stored as a single value of type 323.Vt int . 324.It Dv IPV6_RTHDR Fa "int *" 325Get or set whether the routing header from subsequent packets will be 326provided as ancillary data along with the payload in subsequent 327.Xr recvmsg 2 328calls. 329The header is stored in the following structure in the ancillary data 330returned: 331.Bd -literal 332struct ip6_rthdr { 333 u_int8_t ip6r_nxt; /* next header */ 334 u_int8_t ip6r_len; /* length in units of 8 octets */ 335 u_int8_t ip6r_type; /* routing type */ 336 u_int8_t ip6r_segleft; /* segments left */ 337/* followed by routing-type-specific data */ 338} __packed; 339.Ed 340.Pp 341The 342.Fn inet6_option_space 343routine and family of routines may be used to manipulate this data. 344.Pp 345This option requires superuser privileges. 346.It Dv IPV6_PKTOPTIONS Fa "struct cmsghdr *" 347Get or set all header options and extension headers at one time on the 348last packet sent or received on the socket. 349All options must fit within the size of an mbuf (see 350.Xr mbuf 9 ) . 351Options are specified as a series of 352.Vt cmsghdr 353structures followed by corresponding values. 354.Va cmsg_level 355is set to 356.Dv IPPROTO_IPV6 , 357.Va cmsg_type 358to one of the other values in this list, and trailing data to the option 359value. 360When setting options, if the length 361.Va optlen 362to 363.Xr setsockopt 2 364is zero, all header options will be reset to their default values. 365Otherwise, the length should specify the size the series of control 366messages consumes. 367.Pp 368Instead of using 369.Xr sendmsg 2 370to specify option values, the ancillary data used in these calls that 371correspond to the desired header options may be directly specified as 372the control message in the series of control messages provided as the 373argument to 374.Xr setsockopt 2 . 375.It Dv IPV6_CHECKSUM Fa "int *" 376Get or set the byte offset into a packet where the 16-bit checksum is 377located. 378When set, this byte offset is where incoming packets will be expected 379to have checksums of their data stored and where outgoing packets will 380have checksums of their data computed and stored by the kernel. 381A value of \-1 specifies that no checksums will be checked on incoming 382packets and that no checksums will be computed or stored on outgoing 383packets. 384The offset of the checksum for ICMPv6 sockets cannot be relocated or 385turned off. 386.It Dv IPV6_V6ONLY Fa "int *" 387Get or set whether only IPv6 connections can be made to this socket. 388For wildcard sockets, this can restrict connections to IPv6 only. 389With 390.Ox 391IPv6 sockets are always IPv6-only, so the socket option is read-only 392(not modifiable). 393.It Dv IPV6_FAITH Fa "int *" 394Get or set the status of whether 395.Xr faith 4 396connections can be made to this socket. 397.It Dv IPV6_USE_MIN_MTU Fa "int *" 398Get or set whether the minimal IPv6 maximum transmission unit (MTU) size 399will be used to avoid fragmentation from occurring for subsequent 400outgoing datagrams. 401.It Dv IPV6_AUTH_LEVEL Fa "int *" 402Get or set the 403.Xr ipsec 4 404authentication level. 405.It Dv IPV6_ESP_TRANS_LEVEL Fa "int *" 406Get or set the ESP transport level. 407.It Dv IPV6_ESP_NETWORK_LEVEL Fa "int *" 408Get or set the ESP encapsulation level. 409.It Dv IPV6_IPCOMP_LEVEL Fa "int *" 410Get or set the 411.Xr ipcomp 4 412level. 413.El 414.Pp 415The 416.Dv IPV6_PKTINFO , 417.\" .Dv IPV6_NEXTHOP , 418.Dv IPV6_HOPLIMIT , 419.Dv IPV6_HOPOPTS , 420.Dv IPV6_DSTOPTS , 421and 422.Dv IPV6_RTHDR 423options will return ancillary data along with payload contents in subsequent 424.Xr recvmsg 2 425calls with 426.Va cmsg_level 427set to 428.Dv IPPROTO_IPV6 429and 430.Va cmsg_type 431set to respective option name value (e.g., 432.Dv IPV6_HOPTLIMIT ) . 433These options may also be used directly as ancillary 434.Va cmsg_type 435values in 436.Xr sendmsg 2 437to set options on the packet being transmitted by the call. 438The 439.Va cmsg_level 440value must be 441.Dv IPPROTO_IPV6 . 442For these options, the ancillary data object value format is the same 443as the value returned as explained for each when received with 444.Xr recvmsg 2 . 445.Pp 446Note that using 447.Xr sendmsg 2 448to specify options on particular packets works only on UDP and raw sockets. 449To manipulate header options for packets on TCP sockets, only the socket 450options may be used. 451.Pp 452In some cases, there are multiple APIs defined for manipulating an IPv6 453header field. 454A good example is the outgoing interface for multicast datagrams, which 455can be set by the 456.Dv IPV6_MULTICAST_IF 457socket option, through the 458.Dv IPV6_PKTINFO 459option, and through the 460.Va sin6_scope_id 461field of the socket address passed to the 462.Xr sendto 2 463system call. 464.Pp 465Resolving these conflicts is implementation dependent. 466This implementation determines the value in the following way: 467options specified by using ancillary data (i.e., 468.Xr sendmsg 2 ) 469are considered first, 470options specified by using 471.Dv IPV6_PKTOPTIONS 472to set 473.Dq sticky 474options are considered second, 475options specified by using the individual, basic, and direct socket 476options (e.g., 477.Dv IPV6_UNICAST_HOPS ) 478are considered third, 479and options specified in the socket address supplied to 480.Xr sendto 2 481are the last choice. 482.Ss Multicasting 483IPv6 multicasting is supported only on 484.Dv AF_INET6 485sockets of type 486.Dv SOCK_DGRAM 487and 488.Dv SOCK_RAW , 489and only on networks where the interface driver supports 490multicasting. 491Socket options (see above) that manipulate membership of 492multicast groups and other multicast options include 493.Dv IPV6_MULTICAST_IF , 494.Dv IPV6_MULTICAST_HOPS , 495.Dv IPV6_MULTICAST_LOOP , 496.Dv IPV6_LEAVE_GROUP , 497and 498.Dv IPV6_JOIN_GROUP . 499.Ss Raw Sockets 500Raw IPv6 sockets are connectionless and are normally used with the 501.Xr sendto 2 502and 503.Xr recvfrom 2 504calls, although the 505.Xr connect 2 506call may be used to fix the destination address for future outgoing 507packets so that 508.Xr send 2 509may instead be used and the 510.Xr bind 2 511call may be used to fix the source address for future outgoing 512packets instead of having the kernel choose a source address. 513.Pp 514By using 515.Xr connect 2 516or 517.Xr bind 2 , 518raw socket input is constrained to only packets with their 519source address matching the socket destination address if 520.Xr connect 2 521was used and to packets with their destination address 522matching the socket source address if 523.Xr bind 2 524was used. 525.Pp 526If the 527.Ar proto 528argument to 529.Xr socket 2 530is zero, the default protocol 531.Pq Dv IPPROTO_RAW 532is used for outgoing packets. 533For incoming packets, protocols recognized by kernel are 534.Sy not 535passed to the application socket (e.g., 536.Xr tcp 4 537and 538.Xr udp 4 ) 539except for some ICMPv6 messages. 540The ICMPv6 messages not passed to raw sockets include echo, timestamp, 541and address mask requests. 542If 543.Ar proto 544is non-zero, only packets with this protocol will be passed to the 545socket. 546.Pp 547IPv6 fragments are also not passed to application sockets until 548they have been reassembled. 549If reception of all packets is desired, link-level access (such as 550.Xr bpf 4 ) 551must be used instead. 552.Pp 553Outgoing packets automatically have an IPv6 header prepended to them 554(based on the destination address and the protocol number the socket 555was created with). 556Incoming packets are received by an application without the IPv6 header 557or any extension headers. 558.Pp 559Outgoing packets will be fragmented automatically by the kernel if they 560are too large. 561Incoming packets will be reassembled before being sent to the raw socket, 562so packet fragments or fragment headers will never be seen on a raw socket. 563.Sh EXAMPLES 564The following determines the hop limit on the next packet received: 565.Bd -literal 566struct iovec iov[2]; 567u_char buf[BUFSIZ]; 568struct cmsghdr *cm; 569struct msghdr m; 570int found, optval; 571u_char data[2048]; 572 573/* Create socket. */ 574 575(void)memset(&m, 0, sizeof(m)); 576(void)memset(&iov, 0, sizeof(iov)); 577 578iov[0].iov_base = data; /* buffer for packet payload */ 579iov[0].iov_len = sizeof(data); /* expected packet length */ 580 581m.msg_name = &from; /* sockaddr_in6 of peer */ 582m.msg_namelen = sizeof(from); 583m.msg_iov = iov; 584m.msg_iovlen = 1; 585m.msg_control = (caddr_t)buf; /* buffer for control messages */ 586m.msg_controllen = sizeof(buf); 587 588/* 589 * Enable the hop limit value from received packets to be 590 * returned along with the payload. 591 */ 592optval = 1; 593if (setsockopt(s, IPPROTO_IPV6, IPV6_HOPLIMIT, &optval, 594 sizeof(optval)) == -1) 595 err(1, "setsockopt"); 596 597found = 0; 598while (!found) { 599 if (recvmsg(s, &m, 0) == -1) 600 err(1, "recvmsg"); 601 for (cm = CMSG_FIRSTHDR(&m); cm != NULL; 602 cm = CMSG_NXTHDR(&m, cm)) { 603 if (cm->cmsg_level == IPPROTO_IPV6 && 604 cm->cmsg_type == IPV6_HOPLIMIT && 605 cm->cmsg_len == CMSG_LEN(sizeof(int))) { 606 found = 1; 607 (void)printf("hop limit: %d\en", 608 *(int *)CMSG_DATA(cm)); 609 break; 610 } 611 } 612} 613.Ed 614.Sh DIAGNOSTICS 615A socket operation may fail with one of the following errors returned: 616.Bl -tag -width EADDRNOTAVAILxx 617.It Bq Er EISCONN 618when trying to establish a connection on a socket which 619already has one or when trying to send a datagram with the destination 620address specified and the socket is already connected. 621.It Bq Er ENOTCONN 622when trying to send a datagram, but 623no destination address is specified, and the socket hasn't been 624connected. 625.It Bq Er ENOBUFS 626when the system runs out of memory for 627an internal data structure. 628.It Bq Er EADDRNOTAVAIL 629when an attempt is made to create a 630socket with a network address for which no network interface 631exists. 632.It Bq Er EACCES 633when an attempt is made to create 634a raw IPv6 socket by a non-privileged process. 635.El 636.Pp 637The following errors specific to IPv6 may occur when setting or getting 638header options: 639.Bl -tag -width EADDRNOTAVAILxx 640.It Bq Er EINVAL 641An unknown socket option name was given. 642.It Bq Er EINVAL 643An ancillary data object was improperly formed. 644.El 645.Sh SEE ALSO 646.Xr getsockopt 2 , 647.Xr recv 2 , 648.Xr send 2 , 649.Xr setsockopt 2 , 650.Xr socket 2 , 651.\" .Xr inet6_option_space 3 , 652.\" .Xr inet6_rthdr_space 3 , 653.Xr if_nametoindex 3 , 654.Xr bpf 4 , 655.Xr icmp6 4 , 656.Xr inet6 4 , 657.Xr netintro 4 , 658.Xr tcp 4 , 659.Xr udp 4 660.Rs 661.%A W. Stevens 662.%A M. Thomas 663.%T Advanced Sockets API for IPv6 664.%R RFC 2292 665.%D February 1998 666.Re 667.Rs 668.%A S. Deering 669.%A R. Hinden 670.%T Internet Protocol, Version 6 (IPv6) Specification 671.%R RFC 2460 672.%D December 1998 673.Re 674.Rs 675.%A R. Gilligan 676.%A S. Thomson 677.%A J. Bound 678.%A W. Stevens 679.%T Basic Socket Interface Extensions for IPv6 680.%R RFC 2553 681.%D March 1999 682.Re 683.Rs 684.%A W. Stevens 685.%A B. Fenner 686.%A A. Rudoff 687.%T UNIX Network Programming, third edition 688.Re 689.Sh STANDARDS 690Most of the socket options are defined in RFC 2292 or RFC 2553. 691The 692.Dv IPV6_V6ONLY 693socket option is defined in RFC 3493. 694The 695.Dv IPV6_PORTRANGE 696socket option and the conflict resolution rule are not defined in the 697RFCs and should be considered implementation dependent. 698