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.\" $FreeBSD: src/share/man/man4/ip6.4,v 1.18 2005/01/23 16:02:48 gnn Exp $ 4.\" 5.\" Copyright (c) 1983, 1991, 1993 6.\" The Regents of the University of California. All rights reserved. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.Dd December 22, 2014 32.Dt IP6 4 33.Os 34.Sh NAME 35.Nm ip6 36.Nd Internet Protocol version 6 (IPv6) network layer 37.Sh SYNOPSIS 38.In sys/socket.h 39.In netinet/in.h 40.Ft int 41.Fn socket AF_INET6 SOCK_RAW proto 42.Sh DESCRIPTION 43The IPv6 network layer is used by the IPv6 protocol family for 44transporting data. 45IPv6 packets contain an IPv6 header that is not provided as part of the 46payload contents when passed to an application. 47IPv6 header options affect the behavior of this protocol and may be used 48by high-level protocols (such as the 49.Xr tcp 4 50and 51.Xr udp 4 52protocols) as well as directly by 53.Dq raw sockets , 54which process IPv6 messages at a lower-level and may be useful for 55developing new protocols and special-purpose applications. 56.Ss Header 57All IPv6 packets begin with an IPv6 header. 58When data received by the kernel are passed to the application, this 59header is not included in buffer, even when raw sockets are being used. 60Likewise, when data are sent to the kernel for transmit from the 61application, the buffer is not examined for an IPv6 header: 62the kernel always constructs the header. 63To directly access IPv6 headers from received packets and specify them 64as part of the buffer passed to the kernel, link-level access 65.Po 66.Xr bpf 4 , 67for example 68.Pc 69must instead be utilized. 70.Pp 71The header has the following definition: 72.Bd -literal -offset indent 73struct ip6_hdr { 74 union { 75 struct ip6_hdrctl { 76 u_int32_t ip6_un1_flow; /* 20 bits of flow ID */ 77 u_int16_t ip6_un1_plen; /* payload length */ 78 u_int8_t ip6_un1_nxt; /* next header */ 79 u_int8_t ip6_un1_hlim; /* hop limit */ 80 } ip6_un1; 81 u_int8_t ip6_un2_vfc; /* version and class */ 82 } ip6_ctlun; 83 struct in6_addr ip6_src; /* source address */ 84 struct in6_addr ip6_dst; /* destination address */ 85} __packed; 86 87#define ip6_vfc ip6_ctlun.ip6_un2_vfc 88#define ip6_flow ip6_ctlun.ip6_un1.ip6_un1_flow 89#define ip6_plen ip6_ctlun.ip6_un1.ip6_un1_plen 90#define ip6_nxt ip6_ctlun.ip6_un1.ip6_un1_nxt 91#define ip6_hlim ip6_ctlun.ip6_un1.ip6_un1_hlim 92#define ip6_hops ip6_ctlun.ip6_un1.ip6_un1_hlim 93.Ed 94.Pp 95All fields are in network-byte order. 96Any options specified (see 97.Sx Options 98below) must also be specified in network-byte order. 99.Pp 100.Va ip6_flow 101specifies the flow ID. 102.Va ip6_plen 103specifies the payload length. 104.Va ip6_nxt 105specifies the type of the next header. 106.Va ip6_hlim 107specifies the hop limit. 108.Pp 109The top 4 bits of 110.Va ip6_vfc 111specify the class and the bottom 4 bits specify the version. 112.Pp 113.Va ip6_src 114and 115.Va ip6_dst 116specify the source and destination addresses. 117.Pp 118The IPv6 header may be followed by any number of extension headers that start 119with the following generic definition: 120.Bd -literal -offset indent 121struct ip6_ext { 122 u_int8_t ip6e_nxt; 123 u_int8_t ip6e_len; 124} __packed; 125.Ed 126.Ss Options 127IPv6 allows header options on packets to manipulate the behavior of the 128protocol. 129These options and other control requests are accessed with the 130.Xr getsockopt 2 131and 132.Xr setsockopt 2 133system calls at level 134.Dv IPPROTO_IPV6 135and by using ancillary data in 136.Xr recvmsg 2 137and 138.Xr sendmsg 2 . 139They can be used to access most of the fields in the IPv6 header and 140extension headers. 141.Pp 142The following socket options are supported: 143.Bl -tag -width Ds 144.\" .It Dv IPV6_OPTIONS 145.It Dv IPV6_UNICAST_HOPS Fa "int *" 146Get or set the default hop limit header field for outgoing unicast 147datagrams sent on this socket. 148A value of \-1 resets to the default value. 149.\" .It Dv IPV6_RECVOPTS Fa "int *" 150.\" Get or set the status of whether all header options will be 151.\" delivered along with the datagram when it is received. 152.\" .It Dv IPV6_RECVRETOPTS Fa "int *" 153.\" Get or set the status of whether header options will be delivered 154.\" for reply. 155.\" .It Dv IPV6_RECVDSTADDR Fa "int *" 156.\" Get or set the status of whether datagrams are received with 157.\" destination addresses. 158.\" .It Dv IPV6_RETOPTS 159.\" Get or set IPv6 options. 160.It Dv IPV6_MULTICAST_IF Fa "u_int *" 161Get or set the interface from which multicast packets will be sent. 162For hosts with multiple interfaces, each multicast transmission is sent 163from the primary network interface. 164The interface is specified as its index as provided by 165.Xr if_nametoindex 3 . 166A value of zero specifies the default interface. 167.It Dv IPV6_MULTICAST_HOPS Fa "int *" 168Get or set the default hop limit header field for outgoing multicast 169datagrams sent on this socket. 170This option controls the scope of multicast datagram transmissions. 171.Pp 172Datagrams with a hop limit of 1 are not forwarded beyond the local 173network. 174Multicast datagrams with a hop limit of zero will not be transmitted on 175any network but may be delivered locally if the sending host belongs to 176the destination group and if multicast loopback (see below) has not been 177disabled on the sending socket. 178Multicast datagrams with a hop limit greater than 1 may be forwarded to 179the other networks if a multicast router (such as 180.Xr mrouted 8 ) 181is attached to the local network. 182.It Dv IPV6_MULTICAST_LOOP Fa "u_int *" 183Get or set the status of whether multicast datagrams will be looped back 184for local delivery when a multicast datagram is sent to a group to which 185the sending host belongs. 186.Pp 187This option improves performance for applications that may have no more 188than one instance on a single host (such as a router daemon) by 189eliminating the overhead of receiving their own transmissions. 190It should generally not be used by applications for which there may be 191more than one instance on a single host (such as a conferencing program) 192or for which the sender does not belong to the destination group 193(such as a time-querying program). 194.Pp 195A multicast datagram sent with an initial hop limit greater than 1 may 196be delivered to the sending host on a different interface from that on 197which it was sent if the host belongs to the destination group on that 198other interface. 199The multicast loopback control option has no effect on such delivery. 200.It Dv IPV6_JOIN_GROUP Fa "struct ipv6_mreq *" 201Join a multicast group. 202A host must become a member of a multicast group before it can receive 203datagrams sent to the group. 204.Bd -literal 205struct ipv6_mreq { 206 struct in6_addr ipv6mr_multiaddr; 207 unsigned int ipv6mr_interface; 208}; 209.Ed 210.Pp 211.Va ipv6mr_interface 212may be set to zeroes to choose the default multicast interface or to the 213index of a particular multicast-capable interface if the host is 214multihomed. 215Membership is associated with a single interface; programs running on 216multihomed hosts may need to join the same group on more than one 217interface. 218.Pp 219If the multicast address is unspecified (i.e., all zeroes), messages 220from all multicast addresses will be accepted by this group. 221Note that setting to this value requires superuser privileges. 222.It Dv IPV6_LEAVE_GROUP Fa "struct ipv6_mreq *" 223Drop membership from the associated multicast group. 224Memberships are automatically dropped when the socket is closed or when 225the process exits. 226.It Dv IPV6_PORTRANGE Fa "int *" 227Get or set the allocation policy of ephemeral ports for when the kernel 228automatically binds a local address to this socket. 229The following values are available: 230.Pp 231.Bl -tag -width IPV6_PORTRANGE_DEFAULT -compact 232.It Dv IPV6_PORTRANGE_DEFAULT 233Use the regular range of non-reserved ports (varies, see 234.Xr sysctl 8 ) . 235.It Dv IPV6_PORTRANGE_HIGH 236Use a high range (varies, see 237.Xr sysctl 8 ) . 238.It Dv IPV6_PORTRANGE_LOW 239Use a low, reserved range (600\-1023). 240.El 241.It Dv IPV6_PKTINFO Fa "int *" 242Get or set whether additional information about subsequent packets will 243be provided as ancillary data along with the payload in subsequent 244.Xr recvmsg 2 245calls. 246The information is stored in the following structure in the ancillary 247data returned: 248.Bd -literal 249struct in6_pktinfo { 250 struct in6_addr ipi6_addr; /* src/dst IPv6 address */ 251 unsigned int ipi6_ifindex; /* send/recv if index */ 252}; 253.Ed 254.It Dv IPV6_HOPLIMIT Fa "int *" 255Get or set whether the hop limit header field from subsequent packets 256will be provided as ancillary data along with the payload in subsequent 257.Xr recvmsg 2 258calls. 259The value is stored as an 260.Vt int 261in the ancillary data returned. 262.\" .It Dv IPV6_NEXTHOP Fa "int *" 263.\" Get or set whether the address of the next hop for subsequent 264.\" packets will be provided as ancillary data along with the payload in 265.\" subsequent 266.\" .Xr recvmsg 2 267.\" calls. 268.\" The option is stored as a 269.\" .Vt sockaddr 270.\" structure in the ancillary data returned. 271.\" .Pp 272.\" This option requires superuser privileges. 273.It Dv IPV6_HOPOPTS Fa "int *" 274Get or set whether the hop-by-hop options from subsequent packets will be 275provided as ancillary data along with the payload in subsequent 276.Xr recvmsg 2 277calls. 278The option is stored in the following structure in the ancillary data 279returned: 280.Bd -literal 281struct ip6_hbh { 282 u_int8_t ip6h_nxt; /* next header */ 283 u_int8_t ip6h_len; /* length in units of 8 octets */ 284/* followed by options */ 285} __packed; 286.Ed 287.Pp 288The 289.Fn inet6_option_space 290routine and family of routines may be used to manipulate this data. 291.Pp 292This option requires superuser privileges. 293.It Dv IPV6_DSTOPTS Fa "int *" 294Get or set whether the destination options from subsequent packets will 295be provided as ancillary data along with the payload in subsequent 296.Xr recvmsg 2 297calls. 298The option is stored in the following structure in the ancillary data 299returned: 300.Bd -literal 301struct ip6_dest { 302 u_int8_t ip6d_nxt; /* next header */ 303 u_int8_t ip6d_len; /* length in units of 8 octets */ 304/* followed by options */ 305} __packed; 306.Ed 307.Pp 308The 309.Fn inet6_option_space 310routine and family of routines may be used to manipulate this data. 311.Pp 312This option requires superuser privileges. 313.It Dv IPV6_RTHDR Fa "int *" 314Get or set whether the routing header from subsequent packets will be 315provided as ancillary data along with the payload in subsequent 316.Xr recvmsg 2 317calls. 318The header is stored in the following structure in the ancillary data 319returned: 320.Bd -literal 321struct ip6_rthdr { 322 u_int8_t ip6r_nxt; /* next header */ 323 u_int8_t ip6r_len; /* length in units of 8 octets */ 324 u_int8_t ip6r_type; /* routing type */ 325 u_int8_t ip6r_segleft; /* segments left */ 326/* followed by routing-type-specific data */ 327} __packed; 328.Ed 329.Pp 330The 331.Fn inet6_option_space 332routine and family of routines may be used to manipulate this data. 333.Pp 334This option requires superuser privileges. 335.It Dv IPV6_PKTOPTIONS Fa "struct cmsghdr *" 336Get or set all header options and extension headers at one time on the 337last packet sent or received on the socket. 338All options must fit within the size of an mbuf (see 339.Xr mbuf 9 ) . 340Options are specified as a series of 341.Vt cmsghdr 342structures followed by corresponding values. 343.Va cmsg_level 344is set to 345.Dv IPPROTO_IPV6 , 346.Va cmsg_type 347to one of the other values in this list, and trailing data to the option 348value. 349When setting options, if the length 350.Va optlen 351to 352.Xr setsockopt 2 353is zero, all header options will be reset to their default values. 354Otherwise, the length should specify the size the series of control 355messages consumes. 356.Pp 357Instead of using 358.Xr sendmsg 2 359to specify option values, the ancillary data used in these calls that 360correspond to the desired header options may be directly specified as 361the control message in the series of control messages provided as the 362argument to 363.Xr setsockopt 2 . 364.It Dv IPV6_CHECKSUM Fa "int *" 365Get or set the byte offset into a packet where the 16-bit checksum is 366located. 367When set, this byte offset is where incoming packets will be expected 368to have checksums of their data stored and where outgoing packets will 369have checksums of their data computed and stored by the kernel. 370A value of \-1 specifies that no checksums will be checked on incoming 371packets and that no checksums will be computed or stored on outgoing 372packets. 373The offset of the checksum for ICMPv6 sockets cannot be relocated or 374turned off. 375.It Dv IPV6_V6ONLY Fa "int *" 376Get or set whether only IPv6 connections can be made to this socket. 377For wildcard sockets, this can restrict connections to IPv6 only. 378With 379.Dx , 380the socket option cannot be set to 0 (which will result in returning 381.Er EOPNOTSUPP ) . 382.It Dv IPV6_FAITH Fa "int *" 383Get or set the status of whether 384.Xr faith 4 385connections can be made to this socket. 386.It Dv IPV6_USE_MIN_MTU Fa "int *" 387Get or set whether the minimal IPv6 maximum transmission unit (MTU) size 388will be used to avoid fragmentation from occurring for subsequent 389outgoing datagrams. 390.It Dv IPV6_AUTH_LEVEL Fa "int *" 391Get or set the 392.Xr ipsec 4 393authentication level. 394.It Dv IPV6_ESP_TRANS_LEVEL Fa "int *" 395Get or set the ESP transport level. 396.It Dv IPV6_ESP_NETWORK_LEVEL Fa "int *" 397Get or set the ESP encapsulation level. 398.It Dv IPV6_IPCOMP_LEVEL Fa "int *" 399Get or set the 400.Xr ipcomp 4 401level. 402.El 403.Pp 404The 405.Dv IPV6_PKTINFO , 406.\" .Dv IPV6_NEXTHOP , 407.Dv IPV6_HOPLIMIT , 408.Dv IPV6_HOPOPTS , 409.Dv IPV6_DSTOPTS , 410and 411.Dv IPV6_RTHDR 412options will return ancillary data along with payload contents in subsequent 413.Xr recvmsg 2 414calls with 415.Va cmsg_level 416set to 417.Dv IPPROTO_IPV6 418and 419.Va cmsg_type 420set to respective option name value (e.g., 421.Dv IPV6_HOPTLIMIT ) . 422These options may also be used directly as ancillary 423.Va cmsg_type 424values in 425.Xr sendmsg 2 426to set options on the packet being transmitted by the call. 427The 428.Va cmsg_level 429value must be 430.Dv IPPROTO_IPV6 . 431For these options, the ancillary data object value format is the same 432as the value returned as explained for each when received with 433.Xr recvmsg 2 . 434.Pp 435Note that using 436.Xr sendmsg 2 437to specify options on particular packets works only on UDP and raw sockets. 438To manipulate header options for packets on TCP sockets, only the socket 439options may be used. 440.Pp 441In some cases, there are multiple APIs defined for manipulating an IPv6 442header field. 443A good example is the outgoing interface for multicast datagrams, which 444can be set by the 445.Dv IPV6_MULTICAST_IF 446socket option, through the 447.Dv IPV6_PKTINFO 448option, and through the 449.Va sin6_scope_id 450field of the socket address passed to the 451.Xr sendto 2 452system call. 453.Pp 454Resolving these conflicts is implementation dependent. 455This implementation determines the value in the following way: 456options specified by using ancillary data (i.e., 457.Xr sendmsg 2 ) 458are considered first, 459options specified by using 460.Dv IPV6_PKTOPTIONS 461to set 462.Dq sticky 463options are considered second, 464options specified by using the individual, basic, and direct socket 465options (e.g., 466.Dv IPV6_UNICAST_HOPS ) 467are considered third, 468and options specified in the socket address supplied to 469.Xr sendto 2 470are the last choice. 471.Ss Multicasting 472IPv6 multicasting is supported only on 473.Dv AF_INET6 474sockets of type 475.Dv SOCK_DGRAM 476and 477.Dv SOCK_RAW , 478and only on networks where the interface driver supports 479multicasting. 480Socket options (see above) that manipulate membership of 481multicast groups and other multicast options include 482.Dv IPV6_MULTICAST_IF , 483.Dv IPV6_MULTICAST_HOPS , 484.Dv IPV6_MULTICAST_LOOP , 485.Dv IPV6_LEAVE_GROUP , 486and 487.Dv IPV6_JOIN_GROUP . 488.Ss Raw Sockets 489Raw IPv6 sockets are connectionless and are normally used with the 490.Xr sendto 2 491and 492.Xr recvfrom 2 493calls, although the 494.Xr connect 2 495call may be used to fix the destination address for future outgoing 496packets so that 497.Xr send 2 498may instead be used and the 499.Xr bind 2 500call may be used to fix the source address for future outgoing 501packets instead of having the kernel choose a source address. 502.Pp 503By using 504.Xr connect 2 505or 506.Xr bind 2 , 507raw socket input is constrained to only packets with their 508source address matching the socket destination address if 509.Xr connect 2 510was used and to packets with their destination address 511matching the socket source address if 512.Xr bind 2 513was used. 514.Pp 515If the 516.Ar proto 517argument to 518.Xr socket 2 519is zero, the default protocol 520.Pq Dv IPPROTO_RAW 521is used for outgoing packets. 522For incoming packets, protocols recognized by kernel are 523.Sy not 524passed to the application socket (e.g., 525.Xr tcp 4 526and 527.Xr udp 4 ) 528except for some ICMPv6 messages. 529The ICMPv6 messages not passed to raw sockets include echo, timestamp, 530and address mask requests. 531If 532.Ar proto 533is non-zero, only packets with this protocol will be passed to the 534socket. 535.Pp 536IPv6 fragments are also not passed to application sockets until 537they have been reassembled. 538If reception of all packets is desired, link-level access (such as 539.Xr bpf 4 ) 540must be used instead. 541.Pp 542Outgoing packets automatically have an IPv6 header prepended to them 543(based on the destination address and the protocol number the socket 544was created with). 545Incoming packets are received by an application without the IPv6 header 546or any extension headers. 547.Pp 548Outgoing packets will be fragmented automatically by the kernel if they 549are too large. 550Incoming packets will be reassembled before being sent to the raw socket, 551so packet fragments or fragment headers will never be seen on a raw socket. 552.Sh EXAMPLES 553The following determines the hop limit on the next packet received: 554.Bd -literal 555struct iovec iov[2]; 556u_char buf[BUFSIZ]; 557struct cmsghdr *cm; 558struct msghdr m; 559int found, optval; 560u_char data[2048]; 561 562/* Create socket. */ 563 564(void)memset(&m, 0, sizeof(m)); 565(void)memset(&iov, 0, sizeof(iov)); 566 567iov[0].iov_base = data; /* buffer for packet payload */ 568iov[0].iov_len = sizeof(data); /* expected packet length */ 569 570m.msg_name = &from; /* sockaddr_in6 of peer */ 571m.msg_namelen = sizeof(from); 572m.msg_iov = iov; 573m.msg_iovlen = 1; 574m.msg_control = (caddr_t)buf; /* buffer for control messages */ 575m.msg_controllen = sizeof(buf); 576 577/* 578 * Enable the hop limit value from received packets to be 579 * returned along with the payload. 580 */ 581optval = 1; 582if (setsockopt(s, IPPROTO_IPV6, IPV6_HOPLIMIT, &optval, 583 sizeof(optval)) == -1) 584 err(1, "setsockopt"); 585 586found = 0; 587while (!found) { 588 if (recvmsg(s, &m, 0) == -1) 589 err(1, "recvmsg"); 590 for (cm = CMSG_FIRSTHDR(&m); cm != NULL; 591 cm = CMSG_NXTHDR(&m, cm)) { 592 if (cm->cmsg_level == IPPROTO_IPV6 && 593 cm->cmsg_type == IPV6_HOPLIMIT && 594 cm->cmsg_len == CMSG_LEN(sizeof(int))) { 595 found = 1; 596 (void)printf("hop limit: %d\en", 597 *(int *)CMSG_DATA(cm)); 598 break; 599 } 600 } 601} 602.Ed 603.Sh DIAGNOSTICS 604A socket operation may fail with one of the following errors returned: 605.Bl -tag -width EADDRNOTAVAILxx 606.It Bq Er EISCONN 607when trying to establish a connection on a socket which 608already has one or when trying to send a datagram with the destination 609address specified and the socket is already connected. 610.It Bq Er ENOTCONN 611when trying to send a datagram, but 612no destination address is specified, and the socket hasn't been 613connected. 614.It Bq Er ENOBUFS 615when the system runs out of memory for 616an internal data structure. 617.It Bq Er EADDRNOTAVAIL 618when an attempt is made to create a 619socket with a network address for which no network interface 620exists. 621.It Bq Er EACCES 622when an attempt is made to create 623a raw IPv6 socket by a non-privileged process. 624.El 625.Pp 626The following errors specific to IPv6 may occur when setting or getting 627header options: 628.Bl -tag -width EADDRNOTAVAILxx 629.It Bq Er EINVAL 630An unknown socket option name was given. 631.It Bq Er EINVAL 632An ancillary data object was improperly formed. 633.El 634.Sh SEE ALSO 635.Xr getsockopt 2 , 636.Xr recv 2 , 637.Xr send 2 , 638.Xr setsockopt 2 , 639.Xr socket 2 , 640.\" .Xr inet6_option_space 3 , 641.\" .Xr inet6_rthdr_space 3 , 642.Xr if_nametoindex 3 , 643.Xr bpf 4 , 644.Xr icmp6 4 , 645.Xr inet6 4 , 646.Xr netintro 4 , 647.Xr tcp 4 , 648.Xr udp 4 649.Rs 650.%A W. Stevens 651.%A M. Thomas 652.%T Advanced Sockets API for IPv6 653.%R RFC 2292 654.%D February 1998 655.Re 656.Rs 657.%A S. Deering 658.%A R. Hinden 659.%T Internet Protocol, Version 6 (IPv6) Specification 660.%R RFC 2460 661.%D December 1998 662.Re 663.Rs 664.%A R. Gilligan 665.%A S. Thomson 666.%A J. Bound 667.%A W. Stevens 668.%T Basic Socket Interface Extensions for IPv6 669.%R RFC 2553 670.%D March 1999 671.Re 672.Rs 673.%A W. Stevens 674.%A B. Fenner 675.%A A. Rudoff 676.%T UNIX Network Programming, third edition 677.Re 678.Sh STANDARDS 679Most of the socket options are defined in RFC 2292 or RFC 2553. 680The 681.Dv IPV6_V6ONLY 682socket option is defined in RFC 3542. 683The 684.Dv IPV6_PORTRANGE 685socket option and the conflict resolution rule are not defined in the 686RFCs and should be considered implementation dependent. 687