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.\" 32.Dd December 31, 2019 33.Dt IP6 4 34.Os 35.Sh NAME 36.Nm ip6 37.Nd Internet Protocol version 6 (IPv6) network layer 38.Sh SYNOPSIS 39.In sys/socket.h 40.In netinet/in.h 41.Ft int 42.Fn socket AF_INET6 SOCK_RAW proto 43.Sh DESCRIPTION 44The IPv6 network layer is used by the IPv6 protocol family for 45transporting data. 46IPv6 packets contain an IPv6 header that is not provided as part of the 47payload contents when passed to an application. 48IPv6 header options affect the behavior of this protocol and may be used 49by high-level protocols (such as the 50.Xr tcp 4 51and 52.Xr udp 4 53protocols) as well as directly by 54.Dq raw sockets , 55which process IPv6 messages at a lower-level and may be useful for 56developing new protocols and special-purpose applications. 57.Ss Header 58All IPv6 packets begin with an IPv6 header. 59When data received by the kernel are passed to the application, this 60header is not included in buffer, even when raw sockets are being used. 61Likewise, when data are sent to the kernel for transmit from the 62application, the buffer is not examined for an IPv6 header: 63the kernel always constructs the header. 64To directly access IPv6 headers from received packets and specify them 65as part of the buffer passed to the kernel, link-level access 66.Po 67.Xr bpf 4 , 68for example 69.Pc 70must instead be utilized. 71.Pp 72The header has the following definition: 73.Bd -literal -offset indent 74struct ip6_hdr { 75 union { 76 struct ip6_hdrctl { 77 u_int32_t ip6_un1_flow; /* 20 bits of flow ID */ 78 u_int16_t ip6_un1_plen; /* payload length */ 79 u_int8_t ip6_un1_nxt; /* next header */ 80 u_int8_t ip6_un1_hlim; /* hop limit */ 81 } ip6_un1; 82 u_int8_t ip6_un2_vfc; /* version and class */ 83 } ip6_ctlun; 84 struct in6_addr ip6_src; /* source address */ 85 struct in6_addr ip6_dst; /* destination address */ 86} __packed; 87 88#define ip6_vfc ip6_ctlun.ip6_un2_vfc 89#define ip6_flow ip6_ctlun.ip6_un1.ip6_un1_flow 90#define ip6_plen ip6_ctlun.ip6_un1.ip6_un1_plen 91#define ip6_nxt ip6_ctlun.ip6_un1.ip6_un1_nxt 92#define ip6_hlim ip6_ctlun.ip6_un1.ip6_un1_hlim 93#define ip6_hops ip6_ctlun.ip6_un1.ip6_un1_hlim 94.Ed 95.Pp 96All fields are in network-byte order. 97Any options specified (see 98.Sx Options 99below) must also be specified in network-byte order. 100.Pp 101.Va ip6_flow 102specifies the flow ID. 103.Va ip6_plen 104specifies the payload length. 105.Va ip6_nxt 106specifies the type of the next header. 107.Va ip6_hlim 108specifies the hop limit. 109.Pp 110The top 4 bits of 111.Va ip6_vfc 112specify the class and the bottom 4 bits specify the version. 113.Pp 114.Va ip6_src 115and 116.Va ip6_dst 117specify the source and destination addresses. 118.Pp 119The IPv6 header may be followed by any number of extension headers that start 120with the following generic definition: 121.Bd -literal -offset indent 122struct ip6_ext { 123 u_int8_t ip6e_nxt; 124 u_int8_t ip6e_len; 125} __packed; 126.Ed 127.Ss Options 128IPv6 allows header options on packets to manipulate the behavior of the 129protocol. 130These options and other control requests are accessed with the 131.Xr getsockopt 2 132and 133.Xr setsockopt 2 134system calls at level 135.Dv IPPROTO_IPV6 136and by using ancillary data in 137.Xr recvmsg 2 138and 139.Xr sendmsg 2 . 140They can be used to access most of the fields in the IPv6 header and 141extension headers. 142.Pp 143The following socket options are supported: 144.Bl -tag -width Ds 145.\" .It Dv IPV6_OPTIONS 146.It Dv IPV6_UNICAST_HOPS Fa "int *" 147Get or set the default hop limit header field for outgoing unicast 148datagrams sent on this socket. 149A value of \-1 resets to the default value. 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 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_RTHDR Fa "int *" 315Get or set whether the routing header from subsequent packets will be 316provided as ancillary data along with the payload in subsequent 317.Xr recvmsg 2 318calls. 319The header is stored in the following structure in the ancillary data 320returned: 321.Bd -literal 322struct ip6_rthdr { 323 u_int8_t ip6r_nxt; /* next header */ 324 u_int8_t ip6r_len; /* length in units of 8 octets */ 325 u_int8_t ip6r_type; /* routing type */ 326 u_int8_t ip6r_segleft; /* segments left */ 327/* followed by routing-type-specific data */ 328} __packed; 329.Ed 330.Pp 331The 332.Fn inet6_option_space 333routine and family of routines may be used to manipulate this data. 334.Pp 335This option requires superuser privileges. 336.It Dv IPV6_PKTOPTIONS Fa "struct cmsghdr *" 337Get or set all header options and extension headers at one time on the 338last packet sent or received on the socket. 339All options must fit within the size of an mbuf (see 340.Xr mbuf 9 ) . 341Options are specified as a series of 342.Vt cmsghdr 343structures followed by corresponding values. 344.Va cmsg_level 345is set to 346.Dv IPPROTO_IPV6 , 347.Va cmsg_type 348to one of the other values in this list, and trailing data to the option 349value. 350When setting options, if the length 351.Va optlen 352to 353.Xr setsockopt 2 354is zero, all header options will be reset to their default values. 355Otherwise, the length should specify the size the series of control 356messages consumes. 357.Pp 358Instead of using 359.Xr sendmsg 2 360to specify option values, the ancillary data used in these calls that 361correspond to the desired header options may be directly specified as 362the control message in the series of control messages provided as the 363argument to 364.Xr setsockopt 2 . 365.It Dv IPV6_CHECKSUM Fa "int *" 366Get or set the byte offset into a packet where the 16-bit checksum is 367located. 368When set, this byte offset is where incoming packets will be expected 369to have checksums of their data stored and where outgoing packets will 370have checksums of their data computed and stored by the kernel. 371A value of \-1 specifies that no checksums will be checked on incoming 372packets and that no checksums will be computed or stored on outgoing 373packets. 374The offset of the checksum for ICMPv6 sockets cannot be relocated or 375turned off. 376.It Dv IPV6_V6ONLY Fa "int *" 377Setting this option disallows ipv6<->ipv4 mappings. Clearing this 378option allows such mappings. However, 379.Dx 380no longer implements ipv6<->ipv4 mappings. The value set by this option 381will be ignored and the socketopt will succeed in both cases. 382.Xr getsockopt 2 383for this option will always return a value of 1, indicating that ipv6 384sockets only operate with ipv6 and will not map ipv4. 385.It Dv IPV6_USE_MIN_MTU Fa "int *" 386Get or set whether the minimal IPv6 maximum transmission unit (MTU) size 387will be used to avoid fragmentation from occurring for subsequent 388outgoing datagrams. 389.El 390.Pp 391The 392.Dv IPV6_PKTINFO , 393.\" .Dv IPV6_NEXTHOP , 394.Dv IPV6_HOPLIMIT , 395.Dv IPV6_HOPOPTS , 396.Dv IPV6_DSTOPTS , 397and 398.Dv IPV6_RTHDR 399options will return ancillary data along with payload contents in subsequent 400.Xr recvmsg 2 401calls with 402.Va cmsg_level 403set to 404.Dv IPPROTO_IPV6 405and 406.Va cmsg_type 407set to respective option name value (e.g., 408.Dv IPV6_HOPLIMIT ) . 409These options may also be used directly as ancillary 410.Va cmsg_type 411values in 412.Xr sendmsg 2 413to set options on the packet being transmitted by the call. 414The 415.Va cmsg_level 416value must be 417.Dv IPPROTO_IPV6 . 418For these options, the ancillary data object value format is the same 419as the value returned as explained for each when received with 420.Xr recvmsg 2 . 421.Pp 422Note that using 423.Xr sendmsg 2 424to specify options on particular packets works only on UDP and raw sockets. 425To manipulate header options for packets on TCP sockets, only the socket 426options may be used. 427.Pp 428In some cases, there are multiple APIs defined for manipulating an IPv6 429header field. 430A good example is the outgoing interface for multicast datagrams, which 431can be set by the 432.Dv IPV6_MULTICAST_IF 433socket option, through the 434.Dv IPV6_PKTINFO 435option, and through the 436.Va sin6_scope_id 437field of the socket address passed to the 438.Xr sendto 2 439system call. 440.Pp 441Resolving these conflicts is implementation dependent. 442This implementation determines the value in the following way: 443options specified by using ancillary data (i.e., 444.Xr sendmsg 2 ) 445are considered first, 446options specified by using 447.Dv IPV6_PKTOPTIONS 448to set 449.Dq sticky 450options are considered second, 451options specified by using the individual, basic, and direct socket 452options (e.g., 453.Dv IPV6_UNICAST_HOPS ) 454are considered third, 455and options specified in the socket address supplied to 456.Xr sendto 2 457are the last choice. 458.Ss Multicasting 459IPv6 multicasting is supported only on 460.Dv AF_INET6 461sockets of type 462.Dv SOCK_DGRAM 463and 464.Dv SOCK_RAW , 465and only on networks where the interface driver supports 466multicasting. 467Socket options (see above) that manipulate membership of 468multicast groups and other multicast options include 469.Dv IPV6_MULTICAST_IF , 470.Dv IPV6_MULTICAST_HOPS , 471.Dv IPV6_MULTICAST_LOOP , 472.Dv IPV6_LEAVE_GROUP , 473and 474.Dv IPV6_JOIN_GROUP . 475.Ss Raw Sockets 476Raw IPv6 sockets are connectionless and are normally used with the 477.Xr sendto 2 478and 479.Xr recvfrom 2 480calls, although the 481.Xr connect 2 482call may be used to fix the destination address for future outgoing 483packets so that 484.Xr send 2 485may instead be used and the 486.Xr bind 2 487call may be used to fix the source address for future outgoing 488packets instead of having the kernel choose a source address. 489.Pp 490By using 491.Xr connect 2 492or 493.Xr bind 2 , 494raw socket input is constrained to only packets with their 495source address matching the socket destination address if 496.Xr connect 2 497was used and to packets with their destination address 498matching the socket source address if 499.Xr bind 2 500was used. 501.Pp 502If the 503.Ar proto 504argument to 505.Xr socket 2 506is zero, the default protocol 507.Pq Dv IPPROTO_RAW 508is used for outgoing packets. 509For incoming packets, protocols recognized by kernel are 510.Sy not 511passed to the application socket (e.g., 512.Xr tcp 4 513and 514.Xr udp 4 ) 515except for some ICMPv6 messages. 516The ICMPv6 messages not passed to raw sockets include echo, timestamp, 517and address mask requests. 518If 519.Ar proto 520is non-zero, only packets with this protocol will be passed to the 521socket. 522.Pp 523IPv6 fragments are also not passed to application sockets until 524they have been reassembled. 525If reception of all packets is desired, link-level access (such as 526.Xr bpf 4 ) 527must be used instead. 528.Pp 529Outgoing packets automatically have an IPv6 header prepended to them 530(based on the destination address and the protocol number the socket 531was created with). 532Incoming packets are received by an application without the IPv6 header 533or any extension headers. 534.Pp 535Outgoing packets will be fragmented automatically by the kernel if they 536are too large. 537Incoming packets will be reassembled before being sent to the raw socket, 538so packet fragments or fragment headers will never be seen on a raw socket. 539.Sh EXAMPLES 540The following determines the hop limit on the next packet received: 541.Bd -literal 542struct iovec iov[2]; 543u_char buf[BUFSIZ]; 544struct cmsghdr *cm; 545struct msghdr m; 546int found, optval; 547u_char data[2048]; 548 549/* Create socket. */ 550 551(void)memset(&m, 0, sizeof(m)); 552(void)memset(&iov, 0, sizeof(iov)); 553 554iov[0].iov_base = data; /* buffer for packet payload */ 555iov[0].iov_len = sizeof(data); /* expected packet length */ 556 557m.msg_name = &from; /* sockaddr_in6 of peer */ 558m.msg_namelen = sizeof(from); 559m.msg_iov = iov; 560m.msg_iovlen = 1; 561m.msg_control = (caddr_t)buf; /* buffer for control messages */ 562m.msg_controllen = sizeof(buf); 563 564/* 565 * Enable the hop limit value from received packets to be 566 * returned along with the payload. 567 */ 568optval = 1; 569if (setsockopt(s, IPPROTO_IPV6, IPV6_HOPLIMIT, &optval, 570 sizeof(optval)) == -1) 571 err(1, "setsockopt"); 572 573found = 0; 574while (!found) { 575 if (recvmsg(s, &m, 0) == -1) 576 err(1, "recvmsg"); 577 for (cm = CMSG_FIRSTHDR(&m); cm != NULL; 578 cm = CMSG_NXTHDR(&m, cm)) { 579 if (cm->cmsg_level == IPPROTO_IPV6 && 580 cm->cmsg_type == IPV6_HOPLIMIT && 581 cm->cmsg_len == CMSG_LEN(sizeof(int))) { 582 found = 1; 583 (void)printf("hop limit: %d\en", 584 *(int *)CMSG_DATA(cm)); 585 break; 586 } 587 } 588} 589.Ed 590.Sh DIAGNOSTICS 591A socket operation may fail with one of the following errors returned: 592.Bl -tag -width EADDRNOTAVAILxx 593.It Bq Er EISCONN 594when trying to establish a connection on a socket which 595already has one or when trying to send a datagram with the destination 596address specified and the socket is already connected. 597.It Bq Er ENOTCONN 598when trying to send a datagram, but 599no destination address is specified, and the socket hasn't been 600connected. 601.It Bq Er ENOBUFS 602when the system runs out of memory for 603an internal data structure. 604.It Bq Er EADDRNOTAVAIL 605when an attempt is made to create a 606socket with a network address for which no network interface 607exists. 608.It Bq Er EACCES 609when an attempt is made to create 610a raw IPv6 socket by a non-privileged process. 611.El 612.Pp 613The following errors specific to IPv6 may occur when setting or getting 614header options: 615.Bl -tag -width EADDRNOTAVAILxx 616.It Bq Er EINVAL 617An unknown socket option name was given. 618.It Bq Er EINVAL 619An ancillary data object was improperly formed. 620.El 621.Sh SEE ALSO 622.Xr getsockopt 2 , 623.Xr recv 2 , 624.Xr send 2 , 625.Xr setsockopt 2 , 626.Xr socket 2 , 627.\" .Xr inet6_option_space 3 , 628.\" .Xr inet6_rthdr_space 3 , 629.Xr if_nametoindex 3 , 630.Xr bpf 4 , 631.Xr icmp6 4 , 632.Xr inet6 4 , 633.Xr netintro 4 , 634.Xr tcp 4 , 635.Xr udp 4 636.Rs 637.%A W. Stevens 638.%A M. Thomas 639.%T Advanced Sockets API for IPv6 640.%R RFC 2292 641.%D February 1998 642.Re 643.Rs 644.%A S. Deering 645.%A R. Hinden 646.%T Internet Protocol, Version 6 (IPv6) Specification 647.%R RFC 2460 648.%D December 1998 649.Re 650.Rs 651.%A R. Gilligan 652.%A S. Thomson 653.%A J. Bound 654.%A W. Stevens 655.%T Basic Socket Interface Extensions for IPv6 656.%R RFC 2553 657.%D March 1999 658.Re 659.Rs 660.%A W. Stevens 661.%A B. Fenner 662.%A A. Rudoff 663.%T UNIX Network Programming, third edition 664.Re 665.Sh STANDARDS 666Most of the socket options are defined in RFC 2292 or RFC 2553. 667The 668.Dv IPV6_V6ONLY 669socket option is defined in RFC 3542. 670The 671.Dv IPV6_PORTRANGE 672socket option and the conflict resolution rule are not defined in the 673RFCs and should be considered implementation dependent. 674