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 September 29, 2006 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 u_int32_t ip6_un1_flow; /* 20 bits of flow ID */ 79 u_int16_t ip6_un1_plen; /* payload length */ 80 u_int8_t ip6_un1_nxt; /* next header */ 81 u_int8_t ip6_un1_hlim; /* hop limit */ 82 } ip6_un1; 83 u_int8_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 u_int8_t ip6e_nxt; 125 u_int8_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. 150A value of \-1 resets to the default value. 151.\" .It Dv IPV6_RECVOPTS Fa "int *" 152.\" Get or set the status of whether all header options will be 153.\" delivered along with the datagram when it is received. 154.\" .It Dv IPV6_RECVRETOPTS Fa "int *" 155.\" Get or set the status of whether header options will be delivered 156.\" for reply. 157.\" .It Dv IPV6_RECVDSTADDR Fa "int *" 158.\" Get or set the status of whether datagrams are received with 159.\" destination addresses. 160.\" .It Dv IPV6_RETOPTS 161.\" Get or set IPv6 options. 162.It Dv IPV6_MULTICAST_IF Fa "u_int *" 163Get or set the interface from which multicast packets will be sent. 164For hosts with multiple interfaces, each multicast transmission is sent 165from the primary network interface. 166The interface is specified as its index as provided by 167.Xr if_nametoindex 3 . 168A value of zero specifies the default interface. 169.It Dv IPV6_MULTICAST_HOPS Fa "int *" 170Get or set the default hop limit header field for outgoing multicast 171datagrams sent on this socket. 172This option controls the scope of multicast datagram transmissions. 173.Pp 174Datagrams with a hop limit of 1 are not forwarded beyond the local 175network. 176Multicast datagrams with a hop limit of zero will not be transmitted on 177any network but may be delivered locally if the sending host belongs to 178the destination group and if multicast loopback (see below) has not been 179disabled on the sending socket. 180Multicast datagrams with a hop limit greater than 1 may be forwarded to 181the other networks if a multicast router (such as 182.Xr mrouted 8 Pq Pa ports/net/mrouted ) 183is attached to the local network. 184.It Dv IPV6_MULTICAST_LOOP Fa "u_int *" 185Get or set the status of whether multicast datagrams will be looped back 186for local delivery when a multicast datagram is sent to a group to which 187the sending host belongs. 188.Pp 189This option improves performance for applications that may have no more 190than one instance on a single host (such as a router daemon) by 191eliminating the overhead of receiving their own transmissions. 192It should generally not be used by applications for which there may be 193more than one instance on a single host (such as a conferencing program) 194or for which the sender does not belong to the destination group 195(such as a time-querying program). 196.Pp 197A multicast datagram sent with an initial hop limit greater than 1 may 198be delivered to the sending host on a different interface from that on 199which it was sent if the host belongs to the destination group on that 200other interface. 201The multicast loopback control option has no effect on such delivery. 202.It Dv IPV6_JOIN_GROUP Fa "struct ipv6_mreq *" 203Join a multicast group. 204A host must become a member of a multicast group before it can receive 205datagrams sent to the group. 206.Bd -literal 207struct ipv6_mreq { 208 struct in6_addr ipv6mr_multiaddr; 209 unsigned int ipv6mr_interface; 210}; 211.Ed 212.Pp 213.Va ipv6mr_interface 214may be set to zeroes to choose the default multicast interface or to the 215index of a particular multicast-capable interface if the host is 216multihomed. 217Membership is associated with a single interface; programs running on 218multihomed hosts may need to join the same group on more than one 219interface. 220.Pp 221If the multicast address is unspecified (i.e., all zeroes), messages 222from all multicast addresses will be accepted by this group. 223Note that setting to this value requires superuser privileges. 224.It Dv IPV6_LEAVE_GROUP Fa "struct ipv6_mreq *" 225Drop membership from the associated multicast group. 226Memberships are automatically dropped when the socket is closed or when 227the process exits. 228.It Dv IPV6_PORTRANGE Fa "int *" 229Get or set the allocation policy of ephemeral ports for when the kernel 230automatically binds a local address to this socket. 231The following values are available: 232.Pp 233.Bl -tag -width IPV6_PORTRANGE_DEFAULT -compact 234.It Dv IPV6_PORTRANGE_DEFAULT 235Use the regular range of non-reserved ports (varies, see 236.Xr sysctl 8 ) . 237.It Dv IPV6_PORTRANGE_HIGH 238Use a high range (varies, see 239.Xr sysctl 8 ) . 240.It Dv IPV6_PORTRANGE_LOW 241Use a low, reserved range (600\-1023). 242.El 243.It Dv IPV6_PKTINFO Fa "int *" 244Get or set whether additional information about subsequent packets will 245be provided as ancillary data along with the payload in subsequent 246.Xr recvmsg 2 247calls. 248The information is stored in the following structure in the ancillary 249data returned: 250.Bd -literal 251struct in6_pktinfo { 252 struct in6_addr ipi6_addr; /* src/dst IPv6 address */ 253 unsigned int ipi6_ifindex; /* send/recv if index */ 254}; 255.Ed 256.It Dv IPV6_HOPLIMIT Fa "int *" 257Get or set whether the hop limit header field from subsequent packets 258will be provided as ancillary data along with the payload in subsequent 259.Xr recvmsg 2 260calls. 261The value is stored as an 262.Vt int 263in the ancillary data returned. 264.\" .It Dv IPV6_NEXTHOP Fa "int *" 265.\" Get or set whether the address of the next hop for subsequent 266.\" packets will be provided as ancillary data along with the payload in 267.\" subsequent 268.\" .Xr recvmsg 2 269.\" calls. 270.\" The option is stored as a 271.\" .Vt sockaddr 272.\" structure in the ancillary data returned. 273.\" .Pp 274.\" This option requires superuser privileges. 275.It Dv IPV6_HOPOPTS Fa "int *" 276Get or set whether the hop-by-hop options from subsequent packets will be 277provided as ancillary data along with the payload in subsequent 278.Xr recvmsg 2 279calls. 280The option is stored in the following structure in the ancillary data 281returned: 282.Bd -literal 283struct ip6_hbh { 284 u_int8_t ip6h_nxt; /* next header */ 285 u_int8_t ip6h_len; /* length in units of 8 octets */ 286/* followed by options */ 287} __packed; 288.Ed 289.Pp 290The 291.Fn inet6_option_space 292routine and family of routines may be used to manipulate this data. 293.Pp 294This option requires superuser privileges. 295.It Dv IPV6_DSTOPTS Fa "int *" 296Get or set whether the destination options from subsequent packets will 297be provided as ancillary data along with the payload in subsequent 298.Xr recvmsg 2 299calls. 300The option is stored in the following structure in the ancillary data 301returned: 302.Bd -literal 303struct ip6_dest { 304 u_int8_t ip6d_nxt; /* next header */ 305 u_int8_t ip6d_len; /* length in units of 8 octets */ 306/* followed by options */ 307} __packed; 308.Ed 309.Pp 310The 311.Fn inet6_option_space 312routine and family of routines may be used to manipulate this data. 313.Pp 314This option requires superuser privileges. 315.It Dv IPV6_RTHDR Fa "int *" 316Get or set whether the routing header from subsequent packets will be 317provided as ancillary data along with the payload in subsequent 318.Xr recvmsg 2 319calls. 320The header is stored in the following structure in the ancillary data 321returned: 322.Bd -literal 323struct ip6_rthdr { 324 u_int8_t ip6r_nxt; /* next header */ 325 u_int8_t ip6r_len; /* length in units of 8 octets */ 326 u_int8_t ip6r_type; /* routing type */ 327 u_int8_t ip6r_segleft; /* segments left */ 328/* followed by routing-type-specific data */ 329} __packed; 330.Ed 331.Pp 332The 333.Fn inet6_option_space 334routine and family of routines may be used to manipulate this data. 335.Pp 336This option requires superuser privileges. 337.It Dv IPV6_PKTOPTIONS Fa "struct cmsghdr *" 338Get or set all header options and extension headers at one time on the 339last packet sent or received on the socket. 340All options must fit within the size of an mbuf (see 341.Xr mbuf 9 ) . 342Options are specified as a series of 343.Vt cmsghdr 344structures followed by corresponding values. 345.Va cmsg_level 346is set to 347.Dv IPPROTO_IPV6 , 348.Va cmsg_type 349to one of the other values in this list, and trailing data to the option 350value. 351When setting options, if the length 352.Va optlen 353to 354.Xr setsockopt 2 355is zero, all header options will be reset to their default values. 356Otherwise, the length should specify the size the series of control 357messages consumes. 358.Pp 359Instead of using 360.Xr sendmsg 2 361to specify option values, the ancillary data used in these calls that 362correspond to the desired header options may be directly specified as 363the control message in the series of control messages provided as the 364argument to 365.Xr setsockopt 2 . 366.It Dv IPV6_CHECKSUM Fa "int *" 367Get or set the byte offset into a packet where the 16-bit checksum is 368located. 369When set, this byte offset is where incoming packets will be expected 370to have checksums of their data stored and where outgoing packets will 371have checksums of their data computed and stored by the kernel. 372A value of \-1 specifies that no checksums will be checked on incoming 373packets and that no checksums will be computed or stored on outgoing 374packets. 375The offset of the checksum for ICMPv6 sockets cannot be relocated or 376turned off. 377.It Dv IPV6_V6ONLY Fa "int *" 378Get or set whether only IPv6 connections can be made to this socket. 379For wildcard sockets, this can restrict connections to IPv6 only. 380.\"With 381.\".Ox 382.\"IPv6 sockets are always IPv6-only, so the socket option is read-only 383.\"(not modifiable). 384.It Dv IPV6_FAITH Fa "int *" 385Get or set the status of whether 386.Xr faith 4 387connections can be made to this socket. 388.It Dv IPV6_USE_MIN_MTU Fa "int *" 389Get or set whether the minimal IPv6 maximum transmission unit (MTU) size 390will be used to avoid fragmentation from occurring for subsequent 391outgoing datagrams. 392.It Dv IPV6_AUTH_LEVEL Fa "int *" 393Get or set the 394.Xr ipsec 4 395authentication level. 396.It Dv IPV6_ESP_TRANS_LEVEL Fa "int *" 397Get or set the ESP transport level. 398.It Dv IPV6_ESP_NETWORK_LEVEL Fa "int *" 399Get or set the ESP encapsulation level. 400.It Dv IPV6_IPCOMP_LEVEL Fa "int *" 401Get or set the 402.Xr ipcomp 4 403level. 404.El 405.Pp 406The 407.Dv IPV6_PKTINFO , 408.\" .Dv IPV6_NEXTHOP , 409.Dv IPV6_HOPLIMIT , 410.Dv IPV6_HOPOPTS , 411.Dv IPV6_DSTOPTS , 412and 413.Dv IPV6_RTHDR 414options will return ancillary data along with payload contents in subsequent 415.Xr recvmsg 2 416calls with 417.Va cmsg_level 418set to 419.Dv IPPROTO_IPV6 420and 421.Va cmsg_type 422set to respective option name value (e.g., 423.Dv IPV6_HOPTLIMIT ) . 424These options may also be used directly as ancillary 425.Va cmsg_type 426values in 427.Xr sendmsg 2 428to set options on the packet being transmitted by the call. 429The 430.Va cmsg_level 431value must be 432.Dv IPPROTO_IPV6 . 433For these options, the ancillary data object value format is the same 434as the value returned as explained for each when received with 435.Xr recvmsg 2 . 436.Pp 437Note that using 438.Xr sendmsg 2 439to specify options on particular packets works only on UDP and raw sockets. 440To manipulate header options for packets on TCP sockets, only the socket 441options may be used. 442.Pp 443In some cases, there are multiple APIs defined for manipulating an IPv6 444header field. 445A good example is the outgoing interface for multicast datagrams, which 446can be set by the 447.Dv IPV6_MULTICAST_IF 448socket option, through the 449.Dv IPV6_PKTINFO 450option, and through the 451.Va sin6_scope_id 452field of the socket address passed to the 453.Xr sendto 2 454system call. 455.Pp 456Resolving these conflicts is implementation dependent. 457This implementation determines the value in the following way: 458options specified by using ancillary data (i.e., 459.Xr sendmsg 2 ) 460are considered first, 461options specified by using 462.Dv IPV6_PKTOPTIONS 463to set 464.Dq sticky 465options are considered second, 466options specified by using the individual, basic, and direct socket 467options (e.g., 468.Dv IPV6_UNICAST_HOPS ) 469are considered third, 470and options specified in the socket address supplied to 471.Xr sendto 2 472are the last choice. 473.Ss Multicasting 474IPv6 multicasting is supported only on 475.Dv AF_INET6 476sockets of type 477.Dv SOCK_DGRAM 478and 479.Dv SOCK_RAW , 480and only on networks where the interface driver supports 481multicasting. 482Socket options (see above) that manipulate membership of 483multicast groups and other multicast options include 484.Dv IPV6_MULTICAST_IF , 485.Dv IPV6_MULTICAST_HOPS , 486.Dv IPV6_MULTICAST_LOOP , 487.Dv IPV6_LEAVE_GROUP , 488and 489.Dv IPV6_JOIN_GROUP . 490.Ss Raw Sockets 491Raw IPv6 sockets are connectionless and are normally used with the 492.Xr sendto 2 493and 494.Xr recvfrom 2 495calls, although the 496.Xr connect 2 497call may be used to fix the destination address for future outgoing 498packets so that 499.Xr send 2 500may instead be used and the 501.Xr bind 2 502call may be used to fix the source address for future outgoing 503packets instead of having the kernel choose a source address. 504.Pp 505By using 506.Xr connect 2 507or 508.Xr bind 2 , 509raw socket input is constrained to only packets with their 510source address matching the socket destination address if 511.Xr connect 2 512was used and to packets with their destination address 513matching the socket source address if 514.Xr bind 2 515was used. 516.Pp 517If the 518.Ar proto 519argument to 520.Xr socket 2 521is zero, the default protocol 522.Pq Dv IPPROTO_RAW 523is used for outgoing packets. 524For incoming packets, protocols recognized by kernel are 525.Sy not 526passed to the application socket (e.g., 527.Xr tcp 4 528and 529.Xr udp 4 ) 530except for some ICMPv6 messages. 531The ICMPv6 messages not passed to raw sockets include echo, timestamp, 532and address mask requests. 533If 534.Ar proto 535is non-zero, only packets with this protocol will be passed to the 536socket. 537.Pp 538IPv6 fragments are also not passed to application sockets until 539they have been reassembled. 540If reception of all packets is desired, link-level access (such as 541.Xr bpf 4 ) 542must be used instead. 543.Pp 544Outgoing packets automatically have an IPv6 header prepended to them 545(based on the destination address and the protocol number the socket 546was created with). 547Incoming packets are received by an application without the IPv6 header 548or any extension headers. 549.Pp 550Outgoing packets will be fragmented automatically by the kernel if they 551are too large. 552Incoming packets will be reassembled before being sent to the raw socket, 553so packet fragments or fragment headers will never be seen on a raw socket. 554.Sh EXAMPLES 555The following determines the hop limit on the next packet received: 556.Bd -literal 557struct iovec iov[2]; 558u_char buf[BUFSIZ]; 559struct cmsghdr *cm; 560struct msghdr m; 561int found, optval; 562u_char data[2048]; 563 564/* Create socket. */ 565 566(void)memset(&m, 0, sizeof(m)); 567(void)memset(&iov, 0, sizeof(iov)); 568 569iov[0].iov_base = data; /* buffer for packet payload */ 570iov[0].iov_len = sizeof(data); /* expected packet length */ 571 572m.msg_name = &from; /* sockaddr_in6 of peer */ 573m.msg_namelen = sizeof(from); 574m.msg_iov = iov; 575m.msg_iovlen = 1; 576m.msg_control = (caddr_t)buf; /* buffer for control messages */ 577m.msg_controllen = sizeof(buf); 578 579/* 580 * Enable the hop limit value from received packets to be 581 * returned along with the payload. 582 */ 583optval = 1; 584if (setsockopt(s, IPPROTO_IPV6, IPV6_HOPLIMIT, &optval, 585 sizeof(optval)) == -1) 586 err(1, "setsockopt"); 587 588found = 0; 589while (!found) { 590 if (recvmsg(s, &m, 0) == -1) 591 err(1, "recvmsg"); 592 for (cm = CMSG_FIRSTHDR(&m); cm != NULL; 593 cm = CMSG_NXTHDR(&m, cm)) { 594 if (cm->cmsg_level == IPPROTO_IPV6 && 595 cm->cmsg_type == IPV6_HOPLIMIT && 596 cm->cmsg_len == CMSG_LEN(sizeof(int))) { 597 found = 1; 598 (void)printf("hop limit: %d\en", 599 *(int *)CMSG_DATA(cm)); 600 break; 601 } 602 } 603} 604.Ed 605.Sh DIAGNOSTICS 606A socket operation may fail with one of the following errors returned: 607.Bl -tag -width EADDRNOTAVAILxx 608.It Bq Er EISCONN 609when trying to establish a connection on a socket which 610already has one or when trying to send a datagram with the destination 611address specified and the socket is already connected. 612.It Bq Er ENOTCONN 613when trying to send a datagram, but 614no destination address is specified, and the socket has not been 615connected. 616.It Bq Er ENOBUFS 617when the system runs out of memory for 618an internal data structure. 619.It Bq Er EADDRNOTAVAIL 620when an attempt is made to create a 621socket with a network address for which no network interface 622exists. 623.It Bq Er EACCES 624when an attempt is made to create 625a raw IPv6 socket by a non-privileged process. 626.El 627.Pp 628The following errors specific to IPv6 may occur when setting or getting 629header options: 630.Bl -tag -width EADDRNOTAVAILxx 631.It Bq Er EINVAL 632An unknown socket option name was given. 633.It Bq Er EINVAL 634An ancillary data object was improperly formed. 635.El 636.Sh SEE ALSO 637.Xr getsockopt 2 , 638.Xr recv 2 , 639.Xr send 2 , 640.Xr setsockopt 2 , 641.Xr socket 2 , 642.\" .Xr inet6_option_space 3 , 643.\" .Xr inet6_rthdr_space 3 , 644.Xr if_nametoindex 3 , 645.Xr bpf 4 , 646.Xr icmp6 4 , 647.Xr inet6 4 , 648.Xr netintro 4 , 649.Xr tcp 4 , 650.Xr udp 4 651.Rs 652.%A W. Stevens 653.%A M. Thomas 654.%T Advanced Sockets API for IPv6 655.%R RFC 2292 656.%D February 1998 657.Re 658.Rs 659.%A S. Deering 660.%A R. Hinden 661.%T Internet Protocol, Version 6 (IPv6) Specification 662.%R RFC 2460 663.%D December 1998 664.Re 665.Rs 666.%A R. Gilligan 667.%A S. Thomson 668.%A J. Bound 669.%A W. Stevens 670.%T Basic Socket Interface Extensions for IPv6 671.%R RFC 2553 672.%D March 1999 673.Re 674.Rs 675.%A W. Stevens 676.%A B. Fenner 677.%A A. Rudoff 678.%T UNIX Network Programming, third edition 679.Re 680.Sh STANDARDS 681Most of the socket options are defined in RFC 2292 or RFC 2553. 682The 683.Dv IPV6_V6ONLY 684socket option is defined in RFC 3542. 685The 686.Dv IPV6_PORTRANGE 687socket option and the conflict resolution rule are not defined in the 688RFCs and should be considered implementation dependent. 689