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_RETOPTS 160.\" Get or set IPv6 options. 161.It Dv IPV6_MULTICAST_IF Fa "u_int *" 162Get or set the interface from which multicast packets will be sent. 163For hosts with multiple interfaces, each multicast transmission is sent 164from the primary network interface. 165The interface is specified as its index as provided by 166.Xr if_nametoindex 3 . 167A value of zero specifies the default interface. 168.It Dv IPV6_MULTICAST_HOPS Fa "int *" 169Get or set the default hop limit header field for outgoing multicast 170datagrams sent on this socket. 171This option controls the scope of multicast datagram transmissions. 172.Pp 173Datagrams with a hop limit of 1 are not forwarded beyond the local 174network. 175Multicast datagrams with a hop limit of zero will not be transmitted on 176any network but may be delivered locally if the sending host belongs to 177the destination group and if multicast loopback (see below) has not been 178disabled on the sending socket. 179Multicast datagrams with a hop limit greater than 1 may be forwarded to 180the other networks if a multicast router (such as 181.Xr mrouted 8 Pq Pa ports/net/mrouted ) 182is attached to the local network. 183.It Dv IPV6_MULTICAST_LOOP Fa "u_int *" 184Get or set the status of whether multicast datagrams will be looped back 185for local delivery when a multicast datagram is sent to a group to which 186the sending host belongs. 187.Pp 188This option improves performance for applications that may have no more 189than one instance on a single host (such as a router daemon) by 190eliminating the overhead of receiving their own transmissions. 191It should generally not be used by applications for which there may be 192more than one instance on a single host (such as a conferencing program) 193or for which the sender does not belong to the destination group 194(such as a time-querying program). 195.Pp 196A multicast datagram sent with an initial hop limit greater than 1 may 197be delivered to the sending host on a different interface from that on 198which it was sent if the host belongs to the destination group on that 199other interface. 200The multicast loopback control option has no effect on such delivery. 201.It Dv IPV6_JOIN_GROUP Fa "struct ipv6_mreq *" 202Join a multicast group. 203A host must become a member of a multicast group before it can receive 204datagrams sent to the group. 205.Bd -literal 206struct ipv6_mreq { 207 struct in6_addr ipv6mr_multiaddr; 208 unsigned int ipv6mr_interface; 209}; 210.Ed 211.Pp 212.Va ipv6mr_interface 213may be set to zeroes to choose the default multicast interface or to the 214index of a particular multicast-capable interface if the host is 215multihomed. 216Membership is associated with a single interface; programs running on 217multihomed hosts may need to join the same group on more than one 218interface. 219.Pp 220If the multicast address is unspecified (i.e., all zeroes), messages 221from all multicast addresses will be accepted by this group. 222Note that setting to this value requires superuser privileges. 223.It Dv IPV6_LEAVE_GROUP Fa "struct ipv6_mreq *" 224Drop membership from the associated multicast group. 225Memberships are automatically dropped when the socket is closed or when 226the process exits. 227.It Dv IPV6_PORTRANGE Fa "int *" 228Get or set the allocation policy of ephemeral ports for when the kernel 229automatically binds a local address to this socket. 230The following values are available: 231.Pp 232.Bl -tag -width IPV6_PORTRANGE_DEFAULT -compact 233.It Dv IPV6_PORTRANGE_DEFAULT 234Use the regular range of non-reserved ports (varies, see 235.Xr ip 4 ) . 236.It Dv IPV6_PORTRANGE_HIGH 237Use a high range (varies, see 238.Xr ip 4 ) . 239.It Dv IPV6_PORTRANGE_LOW 240Use a low, reserved range (600\-1023, see 241.Xr ip 4 ) . 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 uint8_t ip6h_nxt; /* next header */ 285 uint8_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 uint8_t ip6d_nxt; /* next header */ 305 uint8_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_TCLASS Fa "int *" 316Get or set the value of the traffic class field used for outgoing datagrams 317on this socket. 318The value must be between \-1 and 255. 319A value of \-1 resets to the default value. 320.It Dv IPV6_RECVTCLASS Fa "int *" 321Get or set the status of whether the traffic class header field will be 322provided as ancillary data along with the payload in subsequent 323.Xr recvmsg 2 324calls. 325The header field is stored as a single value of type 326.Vt int . 327.It Dv IPV6_RTHDR Fa "int *" 328Get or set whether the routing header from subsequent packets will be 329provided as ancillary data along with the payload in subsequent 330.Xr recvmsg 2 331calls. 332The header is stored in the following structure in the ancillary data 333returned: 334.Bd -literal 335struct ip6_rthdr { 336 uint8_t ip6r_nxt; /* next header */ 337 uint8_t ip6r_len; /* length in units of 8 octets */ 338 uint8_t ip6r_type; /* routing type */ 339 uint8_t ip6r_segleft; /* segments left */ 340/* followed by routing-type-specific data */ 341} __packed; 342.Ed 343.Pp 344The 345.Fn inet6_option_space 346routine and family of routines may be used to manipulate this data. 347.Pp 348This option requires superuser privileges. 349.It Dv IPV6_PKTOPTIONS Fa "struct cmsghdr *" 350Get or set all header options and extension headers at one time on the 351last packet sent or received on the socket. 352All options must fit within the size of an mbuf (see 353.Xr mbuf 9 ) . 354Options are specified as a series of 355.Vt cmsghdr 356structures followed by corresponding values. 357.Va cmsg_level 358is set to 359.Dv IPPROTO_IPV6 , 360.Va cmsg_type 361to one of the other values in this list, and trailing data to the option 362value. 363When setting options, if the length 364.Va optlen 365to 366.Xr setsockopt 2 367is zero, all header options will be reset to their default values. 368Otherwise, the length should specify the size the series of control 369messages consumes. 370.Pp 371Instead of using 372.Xr sendmsg 2 373to specify option values, the ancillary data used in these calls that 374correspond to the desired header options may be directly specified as 375the control message in the series of control messages provided as the 376argument to 377.Xr setsockopt 2 . 378.It Dv IPV6_CHECKSUM Fa "int *" 379Get or set the byte offset into a packet where the 16-bit checksum is 380located. 381When set, this byte offset is where incoming packets will be expected 382to have checksums of their data stored and where outgoing packets will 383have checksums of their data computed and stored by the kernel. 384A value of \-1 specifies that no checksums will be checked on incoming 385packets and that no checksums will be computed or stored on outgoing 386packets. 387The offset of the checksum for ICMPv6 sockets cannot be relocated or 388turned off. 389.It Dv IPV6_V6ONLY Fa "int *" 390Get or set whether only IPv6 connections can be made to this socket. 391For wildcard sockets, this can restrict connections to IPv6 only. 392.\"With 393.\".Ox 394.\"IPv6 sockets are always IPv6-only, so the socket option is read-only 395.\"(not modifiable). 396.It Dv IPV6_USE_MIN_MTU Fa "int *" 397Get or set whether the minimal IPv6 maximum transmission unit (MTU) size 398will be used to avoid fragmentation from occurring for subsequent 399outgoing datagrams. 400.It Dv IPV6_AUTH_LEVEL Fa "int *" 401Get or set the 402.Xr ipsec 4 403authentication level. 404.It Dv IPV6_ESP_TRANS_LEVEL Fa "int *" 405Get or set the ESP transport level. 406.It Dv IPV6_ESP_NETWORK_LEVEL Fa "int *" 407Get or set the ESP encapsulation level. 408.It Dv IPV6_IPCOMP_LEVEL Fa "int *" 409Get or set the 410.Xr ipcomp 4 411level. 412.El 413.Pp 414The 415.Dv IPV6_PKTINFO , 416.\" .Dv IPV6_NEXTHOP , 417.Dv IPV6_HOPLIMIT , 418.Dv IPV6_HOPOPTS , 419.Dv IPV6_DSTOPTS , 420and 421.Dv IPV6_RTHDR 422options will return ancillary data along with payload contents in subsequent 423.Xr recvmsg 2 424calls with 425.Va cmsg_level 426set to 427.Dv IPPROTO_IPV6 428and 429.Va cmsg_type 430set to respective option name value (e.g., 431.Dv IPV6_HOPTLIMIT ) . 432These options may also be used directly as ancillary 433.Va cmsg_type 434values in 435.Xr sendmsg 2 436to set options on the packet being transmitted by the call. 437The 438.Va cmsg_level 439value must be 440.Dv IPPROTO_IPV6 . 441For these options, the ancillary data object value format is the same 442as the value returned as explained for each when received with 443.Xr recvmsg 2 . 444.Pp 445Note that using 446.Xr sendmsg 2 447to specify options on particular packets works only on UDP and raw sockets. 448To manipulate header options for packets on TCP sockets, only the socket 449options may be used. 450.Pp 451In some cases, there are multiple APIs defined for manipulating an IPv6 452header field. 453A good example is the outgoing interface for multicast datagrams, which 454can be set by the 455.Dv IPV6_MULTICAST_IF 456socket option, through the 457.Dv IPV6_PKTINFO 458option, and through the 459.Va sin6_scope_id 460field of the socket address passed to the 461.Xr sendto 2 462system call. 463.Pp 464Resolving these conflicts is implementation dependent. 465This implementation determines the value in the following way: 466options specified by using ancillary data (i.e., 467.Xr sendmsg 2 ) 468are considered first, 469options specified by using 470.Dv IPV6_PKTOPTIONS 471to set 472.Dq sticky 473options are considered second, 474options specified by using the individual, basic, and direct socket 475options (e.g., 476.Dv IPV6_UNICAST_HOPS ) 477are considered third, 478and options specified in the socket address supplied to 479.Xr sendto 2 480are the last choice. 481.Ss Multicasting 482IPv6 multicasting is supported only on 483.Dv AF_INET6 484sockets of type 485.Dv SOCK_DGRAM 486and 487.Dv SOCK_RAW , 488and only on networks where the interface driver supports 489multicasting. 490Socket options (see above) that manipulate membership of 491multicast groups and other multicast options include 492.Dv IPV6_MULTICAST_IF , 493.Dv IPV6_MULTICAST_HOPS , 494.Dv IPV6_MULTICAST_LOOP , 495.Dv IPV6_LEAVE_GROUP , 496and 497.Dv IPV6_JOIN_GROUP . 498.Ss Raw Sockets 499Raw IPv6 sockets are connectionless and are normally used with the 500.Xr sendto 2 501and 502.Xr recvfrom 2 503calls, although the 504.Xr connect 2 505call may be used to fix the destination address for future outgoing 506packets so that 507.Xr send 2 508may instead be used and the 509.Xr bind 2 510call may be used to fix the source address for future outgoing 511packets instead of having the kernel choose a source address. 512.Pp 513By using 514.Xr connect 2 515or 516.Xr bind 2 , 517raw socket input is constrained to only packets with their 518source address matching the socket destination address if 519.Xr connect 2 520was used and to packets with their destination address 521matching the socket source address if 522.Xr bind 2 523was used. 524.Pp 525If the 526.Ar proto 527argument to 528.Xr socket 2 529is zero, the default protocol 530.Pq Dv IPPROTO_RAW 531is used for outgoing packets. 532For incoming packets, protocols recognized by kernel are 533.Sy not 534passed to the application socket (e.g., 535.Xr tcp 4 536and 537.Xr udp 4 ) 538except for some ICMPv6 messages. 539The ICMPv6 messages not passed to raw sockets include echo, timestamp, 540and address mask requests. 541If 542.Ar proto 543is non-zero, only packets with this protocol will be passed to the 544socket. 545.Pp 546IPv6 fragments are also not passed to application sockets until 547they have been reassembled. 548If reception of all packets is desired, link-level access (such as 549.Xr bpf 4 ) 550must be used instead. 551.Pp 552Outgoing packets automatically have an IPv6 header prepended to them 553(based on the destination address and the protocol number the socket 554was created with). 555Incoming packets are received by an application without the IPv6 header 556or any extension headers. 557.Pp 558Outgoing packets will be fragmented automatically by the kernel if they 559are too large. 560Incoming packets will be reassembled before being sent to the raw socket, 561so packet fragments or fragment headers will never be seen on a raw socket. 562.Sh EXAMPLES 563The following determines the hop limit on the next packet received: 564.Bd -literal 565struct iovec iov[2]; 566u_char buf[BUFSIZ]; 567struct cmsghdr *cm; 568struct msghdr m; 569int optval; 570bool found; 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 = false; 598do { 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 = true; 607 (void)printf("hop limit: %d\en", 608 *(int *)CMSG_DATA(cm)); 609 break; 610 } 611 } 612} while (!found); 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 has not 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 ip 4 , 658.Xr netintro 4 , 659.Xr tcp 4 , 660.Xr udp 4 661.Rs 662.%A W. Stevens 663.%A M. Thomas 664.%T Advanced Sockets API for IPv6 665.%R RFC 2292 666.%D February 1998 667.Re 668.Rs 669.%A S. Deering 670.%A R. Hinden 671.%T Internet Protocol, Version 6 (IPv6) Specification 672.%R RFC 2460 673.%D December 1998 674.Re 675.Rs 676.%A R. Gilligan 677.%A S. Thomson 678.%A J. Bound 679.%A W. Stevens 680.%T Basic Socket Interface Extensions for IPv6 681.%R RFC 2553 682.%D March 1999 683.Re 684.Rs 685.%A W. Stevens 686.%A B. Fenner 687.%A A. Rudoff 688.%T UNIX Network Programming, third edition 689.Re 690.Sh STANDARDS 691Most of the socket options are defined in RFC 2292 or RFC 2553. 692The 693.Dv IPV6_V6ONLY 694socket option is defined in RFC 3493 Section 5.3. 695The 696.Dv IPV6_PORTRANGE 697socket option and the conflict resolution rule are not defined in the 698RFCs and should be considered implementation dependent. 699