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 February 21, 2008 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. 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 sysctl 8 ) . 236.It Dv IPV6_PORTRANGE_HIGH 237Use a high range (varies, see 238.Xr sysctl 8 ) . 239.It Dv IPV6_PORTRANGE_LOW 240Use a low, reserved range (600\-1023). 241.El 242.It Dv IPV6_PKTINFO Fa "int *" 243Get or set whether additional information about subsequent packets will 244be provided as ancillary data along with the payload in subsequent 245.Xr recvmsg 2 246calls. 247The information is stored in the following structure in the ancillary 248data returned: 249.Bd -literal 250struct in6_pktinfo { 251 struct in6_addr ipi6_addr; /* src/dst IPv6 address */ 252 unsigned int ipi6_ifindex; /* send/recv if index */ 253}; 254.Ed 255.It Dv IPV6_HOPLIMIT Fa "int *" 256Get or set whether the hop limit header field from subsequent packets 257will be provided as ancillary data along with the payload in subsequent 258.Xr recvmsg 2 259calls. 260The value is stored as an 261.Vt int 262in the ancillary data returned. 263.\" .It Dv IPV6_NEXTHOP Fa "int *" 264.\" Get or set whether the address of the next hop for subsequent 265.\" packets will be provided as ancillary data along with the payload in 266.\" subsequent 267.\" .Xr recvmsg 2 268.\" calls. 269.\" The option is stored as a 270.\" .Vt sockaddr 271.\" structure in the ancillary data returned. 272.\" .Pp 273.\" This option requires superuser privileges. 274.It Dv IPV6_HOPOPTS Fa "int *" 275Get or set whether the hop-by-hop options from subsequent packets will be 276provided as ancillary data along with the payload in subsequent 277.Xr recvmsg 2 278calls. 279The option is stored in the following structure in the ancillary data 280returned: 281.Bd -literal 282struct ip6_hbh { 283 u_int8_t ip6h_nxt; /* next header */ 284 u_int8_t ip6h_len; /* length in units of 8 octets */ 285/* followed by options */ 286} __packed; 287.Ed 288.Pp 289The 290.Fn inet6_option_space 291routine and family of routines may be used to manipulate this data. 292.Pp 293This option requires superuser privileges. 294.It Dv IPV6_DSTOPTS Fa "int *" 295Get or set whether the destination options from subsequent packets will 296be provided as ancillary data along with the payload in subsequent 297.Xr recvmsg 2 298calls. 299The option is stored in the following structure in the ancillary data 300returned: 301.Bd -literal 302struct ip6_dest { 303 u_int8_t ip6d_nxt; /* next header */ 304 u_int8_t ip6d_len; /* length in units of 8 octets */ 305/* followed by options */ 306} __packed; 307.Ed 308.Pp 309The 310.Fn inet6_option_space 311routine and family of routines may be used to manipulate this data. 312.Pp 313This option requires superuser privileges. 314.It Dv IPV6_TCLASS Fa "int *" 315Get or set the value of the traffic class field used for outgoing datagrams 316on this socket. 317The value must be between \-1 and 255. 318A value of \-1 resets to the default value. 319.It Dv IPV6_RECVTCLASS Fa "int *" 320Get or set the status of whether the traffic class header field will be 321provided as ancillary data along with the payload in subsequent 322.Xr recvmsg 2 323calls. 324The header field is stored as a single value of type 325.Vt int . 326.It Dv IPV6_RTHDR Fa "int *" 327Get or set whether the routing header from subsequent packets will be 328provided as ancillary data along with the payload in subsequent 329.Xr recvmsg 2 330calls. 331The header is stored in the following structure in the ancillary data 332returned: 333.Bd -literal 334struct ip6_rthdr { 335 u_int8_t ip6r_nxt; /* next header */ 336 u_int8_t ip6r_len; /* length in units of 8 octets */ 337 u_int8_t ip6r_type; /* routing type */ 338 u_int8_t ip6r_segleft; /* segments left */ 339/* followed by routing-type-specific data */ 340} __packed; 341.Ed 342.Pp 343The 344.Fn inet6_option_space 345routine and family of routines may be used to manipulate this data. 346.Pp 347This option requires superuser privileges. 348.It Dv IPV6_PKTOPTIONS Fa "struct cmsghdr *" 349Get or set all header options and extension headers at one time on the 350last packet sent or received on the socket. 351All options must fit within the size of an mbuf (see 352.Xr mbuf 9 ) . 353Options are specified as a series of 354.Vt cmsghdr 355structures followed by corresponding values. 356.Va cmsg_level 357is set to 358.Dv IPPROTO_IPV6 , 359.Va cmsg_type 360to one of the other values in this list, and trailing data to the option 361value. 362When setting options, if the length 363.Va optlen 364to 365.Xr setsockopt 2 366is zero, all header options will be reset to their default values. 367Otherwise, the length should specify the size the series of control 368messages consumes. 369.Pp 370Instead of using 371.Xr sendmsg 2 372to specify option values, the ancillary data used in these calls that 373correspond to the desired header options may be directly specified as 374the control message in the series of control messages provided as the 375argument to 376.Xr setsockopt 2 . 377.It Dv IPV6_CHECKSUM Fa "int *" 378Get or set the byte offset into a packet where the 16-bit checksum is 379located. 380When set, this byte offset is where incoming packets will be expected 381to have checksums of their data stored and where outgoing packets will 382have checksums of their data computed and stored by the kernel. 383A value of \-1 specifies that no checksums will be checked on incoming 384packets and that no checksums will be computed or stored on outgoing 385packets. 386The offset of the checksum for ICMPv6 sockets cannot be relocated or 387turned off. 388.It Dv IPV6_V6ONLY Fa "int *" 389Get or set whether only IPv6 connections can be made to this socket. 390For wildcard sockets, this can restrict connections to IPv6 only. 391.\"With 392.\".Ox 393.\"IPv6 sockets are always IPv6-only, so the socket option is read-only 394.\"(not modifiable). 395.It Dv IPV6_FAITH Fa "int *" 396Get or set the status of whether 397.Xr faith 4 398connections can be made to this socket. 399.It Dv IPV6_USE_MIN_MTU Fa "int *" 400Get or set whether the minimal IPv6 maximum transmission unit (MTU) size 401will be used to avoid fragmentation from occurring for subsequent 402outgoing datagrams. 403.It Dv IPV6_AUTH_LEVEL Fa "int *" 404Get or set the 405.Xr ipsec 4 406authentication level. 407.It Dv IPV6_ESP_TRANS_LEVEL Fa "int *" 408Get or set the ESP transport level. 409.It Dv IPV6_ESP_NETWORK_LEVEL Fa "int *" 410Get or set the ESP encapsulation level. 411.It Dv IPV6_IPCOMP_LEVEL Fa "int *" 412Get or set the 413.Xr ipcomp 4 414level. 415.El 416.Pp 417The 418.Dv IPV6_PKTINFO , 419.\" .Dv IPV6_NEXTHOP , 420.Dv IPV6_HOPLIMIT , 421.Dv IPV6_HOPOPTS , 422.Dv IPV6_DSTOPTS , 423and 424.Dv IPV6_RTHDR 425options will return ancillary data along with payload contents in subsequent 426.Xr recvmsg 2 427calls with 428.Va cmsg_level 429set to 430.Dv IPPROTO_IPV6 431and 432.Va cmsg_type 433set to respective option name value (e.g., 434.Dv IPV6_HOPTLIMIT ) . 435These options may also be used directly as ancillary 436.Va cmsg_type 437values in 438.Xr sendmsg 2 439to set options on the packet being transmitted by the call. 440The 441.Va cmsg_level 442value must be 443.Dv IPPROTO_IPV6 . 444For these options, the ancillary data object value format is the same 445as the value returned as explained for each when received with 446.Xr recvmsg 2 . 447.Pp 448Note that using 449.Xr sendmsg 2 450to specify options on particular packets works only on UDP and raw sockets. 451To manipulate header options for packets on TCP sockets, only the socket 452options may be used. 453.Pp 454In some cases, there are multiple APIs defined for manipulating an IPv6 455header field. 456A good example is the outgoing interface for multicast datagrams, which 457can be set by the 458.Dv IPV6_MULTICAST_IF 459socket option, through the 460.Dv IPV6_PKTINFO 461option, and through the 462.Va sin6_scope_id 463field of the socket address passed to the 464.Xr sendto 2 465system call. 466.Pp 467Resolving these conflicts is implementation dependent. 468This implementation determines the value in the following way: 469options specified by using ancillary data (i.e., 470.Xr sendmsg 2 ) 471are considered first, 472options specified by using 473.Dv IPV6_PKTOPTIONS 474to set 475.Dq sticky 476options are considered second, 477options specified by using the individual, basic, and direct socket 478options (e.g., 479.Dv IPV6_UNICAST_HOPS ) 480are considered third, 481and options specified in the socket address supplied to 482.Xr sendto 2 483are the last choice. 484.Ss Multicasting 485IPv6 multicasting is supported only on 486.Dv AF_INET6 487sockets of type 488.Dv SOCK_DGRAM 489and 490.Dv SOCK_RAW , 491and only on networks where the interface driver supports 492multicasting. 493Socket options (see above) that manipulate membership of 494multicast groups and other multicast options include 495.Dv IPV6_MULTICAST_IF , 496.Dv IPV6_MULTICAST_HOPS , 497.Dv IPV6_MULTICAST_LOOP , 498.Dv IPV6_LEAVE_GROUP , 499and 500.Dv IPV6_JOIN_GROUP . 501.Ss Raw Sockets 502Raw IPv6 sockets are connectionless and are normally used with the 503.Xr sendto 2 504and 505.Xr recvfrom 2 506calls, although the 507.Xr connect 2 508call may be used to fix the destination address for future outgoing 509packets so that 510.Xr send 2 511may instead be used and the 512.Xr bind 2 513call may be used to fix the source address for future outgoing 514packets instead of having the kernel choose a source address. 515.Pp 516By using 517.Xr connect 2 518or 519.Xr bind 2 , 520raw socket input is constrained to only packets with their 521source address matching the socket destination address if 522.Xr connect 2 523was used and to packets with their destination address 524matching the socket source address if 525.Xr bind 2 526was used. 527.Pp 528If the 529.Ar proto 530argument to 531.Xr socket 2 532is zero, the default protocol 533.Pq Dv IPPROTO_RAW 534is used for outgoing packets. 535For incoming packets, protocols recognized by kernel are 536.Sy not 537passed to the application socket (e.g., 538.Xr tcp 4 539and 540.Xr udp 4 ) 541except for some ICMPv6 messages. 542The ICMPv6 messages not passed to raw sockets include echo, timestamp, 543and address mask requests. 544If 545.Ar proto 546is non-zero, only packets with this protocol will be passed to the 547socket. 548.Pp 549IPv6 fragments are also not passed to application sockets until 550they have been reassembled. 551If reception of all packets is desired, link-level access (such as 552.Xr bpf 4 ) 553must be used instead. 554.Pp 555Outgoing packets automatically have an IPv6 header prepended to them 556(based on the destination address and the protocol number the socket 557was created with). 558Incoming packets are received by an application without the IPv6 header 559or any extension headers. 560.Pp 561Outgoing packets will be fragmented automatically by the kernel if they 562are too large. 563Incoming packets will be reassembled before being sent to the raw socket, 564so packet fragments or fragment headers will never be seen on a raw socket. 565.Sh EXAMPLES 566The following determines the hop limit on the next packet received: 567.Bd -literal 568struct iovec iov[2]; 569u_char buf[BUFSIZ]; 570struct cmsghdr *cm; 571struct msghdr m; 572int found, optval; 573u_char data[2048]; 574 575/* Create socket. */ 576 577(void)memset(&m, 0, sizeof(m)); 578(void)memset(&iov, 0, sizeof(iov)); 579 580iov[0].iov_base = data; /* buffer for packet payload */ 581iov[0].iov_len = sizeof(data); /* expected packet length */ 582 583m.msg_name = &from; /* sockaddr_in6 of peer */ 584m.msg_namelen = sizeof(from); 585m.msg_iov = iov; 586m.msg_iovlen = 1; 587m.msg_control = (caddr_t)buf; /* buffer for control messages */ 588m.msg_controllen = sizeof(buf); 589 590/* 591 * Enable the hop limit value from received packets to be 592 * returned along with the payload. 593 */ 594optval = 1; 595if (setsockopt(s, IPPROTO_IPV6, IPV6_HOPLIMIT, &optval, 596 sizeof(optval)) == -1) 597 err(1, "setsockopt"); 598 599found = 0; 600while (!found) { 601 if (recvmsg(s, &m, 0) == -1) 602 err(1, "recvmsg"); 603 for (cm = CMSG_FIRSTHDR(&m); cm != NULL; 604 cm = CMSG_NXTHDR(&m, cm)) { 605 if (cm->cmsg_level == IPPROTO_IPV6 && 606 cm->cmsg_type == IPV6_HOPLIMIT && 607 cm->cmsg_len == CMSG_LEN(sizeof(int))) { 608 found = 1; 609 (void)printf("hop limit: %d\en", 610 *(int *)CMSG_DATA(cm)); 611 break; 612 } 613 } 614} 615.Ed 616.Sh DIAGNOSTICS 617A socket operation may fail with one of the following errors returned: 618.Bl -tag -width EADDRNOTAVAILxx 619.It Bq Er EISCONN 620when trying to establish a connection on a socket which 621already has one or when trying to send a datagram with the destination 622address specified and the socket is already connected. 623.It Bq Er ENOTCONN 624when trying to send a datagram, but 625no destination address is specified, and the socket has not been 626connected. 627.It Bq Er ENOBUFS 628when the system runs out of memory for 629an internal data structure. 630.It Bq Er EADDRNOTAVAIL 631when an attempt is made to create a 632socket with a network address for which no network interface 633exists. 634.It Bq Er EACCES 635when an attempt is made to create 636a raw IPv6 socket by a non-privileged process. 637.El 638.Pp 639The following errors specific to IPv6 may occur when setting or getting 640header options: 641.Bl -tag -width EADDRNOTAVAILxx 642.It Bq Er EINVAL 643An unknown socket option name was given. 644.It Bq Er EINVAL 645An ancillary data object was improperly formed. 646.El 647.Sh SEE ALSO 648.Xr getsockopt 2 , 649.Xr recv 2 , 650.Xr send 2 , 651.Xr setsockopt 2 , 652.Xr socket 2 , 653.\" .Xr inet6_option_space 3 , 654.\" .Xr inet6_rthdr_space 3 , 655.Xr if_nametoindex 3 , 656.Xr bpf 4 , 657.Xr icmp6 4 , 658.Xr inet6 4 , 659.Xr netintro 4 , 660.Xr tcp 4 , 661.Xr udp 4 662.Rs 663.%A W. Stevens 664.%A M. Thomas 665.%T Advanced Sockets API for IPv6 666.%R RFC 2292 667.%D February 1998 668.Re 669.Rs 670.%A S. Deering 671.%A R. Hinden 672.%T Internet Protocol, Version 6 (IPv6) Specification 673.%R RFC 2460 674.%D December 1998 675.Re 676.Rs 677.%A R. Gilligan 678.%A S. Thomson 679.%A J. Bound 680.%A W. Stevens 681.%T Basic Socket Interface Extensions for IPv6 682.%R RFC 2553 683.%D March 1999 684.Re 685.Rs 686.%A W. Stevens 687.%A B. Fenner 688.%A A. Rudoff 689.%T UNIX Network Programming, third edition 690.Re 691.Sh STANDARDS 692Most of the socket options are defined in RFC 2292 or RFC 2553. 693The 694.Dv IPV6_V6ONLY 695socket option is defined in RFC 3493 Section 5.3. 696The 697.Dv IPV6_PORTRANGE 698socket option and the conflict resolution rule are not defined in the 699RFCs and should be considered implementation dependent. 700