c557ae16ce
a server process bound to a wildcard UDP socket to select the IP address from which outgoing packets are sent on a per-datagram basis. When combined with IP_RECVDSTADDR, such a server process can guarantee to reply to an incoming request using the same source IP address as the destination IP address of the request, without having to open one socket per server IP address. Discussed on: -net Approved by: re
451 lines
12 KiB
Groff
451 lines
12 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)ip.4 8.2 (Berkeley) 11/30/93
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.\" $FreeBSD$
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.\"
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.Dd March 3, 2001
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.Dt IP 4
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.Os
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.Sh NAME
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.Nm ip
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.Nd Internet Protocol
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/socket.h
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.In netinet/in.h
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.Ft int
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.Fn socket AF_INET SOCK_RAW proto
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.Sh DESCRIPTION
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.Tn IP
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is the transport layer protocol used
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by the Internet protocol family.
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Options may be set at the
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.Tn IP
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level
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when using higher-level protocols that are based on
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.Tn IP
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(such as
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.Tn TCP
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and
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.Tn UDP ) .
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It may also be accessed
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through a
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.Dq raw socket
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when developing new protocols, or
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special-purpose applications.
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.Pp
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There are several
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.Tn IP-level
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.Xr setsockopt 2
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and
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.Xr getsockopt 2
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options.
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.Dv IP_OPTIONS
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may be used to provide
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.Tn IP
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options to be transmitted in the
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.Tn IP
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header of each outgoing packet
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or to examine the header options on incoming packets.
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.Tn IP
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options may be used with any socket type in the Internet family.
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The format of
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.Tn IP
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options to be sent is that specified by the
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.Tn IP
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protocol specification (RFC-791), with one exception:
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the list of addresses for Source Route options must include the first-hop
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gateway at the beginning of the list of gateways.
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The first-hop gateway address will be extracted from the option list
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and the size adjusted accordingly before use.
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To disable previously specified options,
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use a zero-length buffer:
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.Bd -literal
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setsockopt(s, IPPROTO_IP, IP_OPTIONS, NULL, 0);
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.Ed
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.Pp
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.Dv IP_TOS
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and
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.Dv IP_TTL
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may be used to set the type-of-service and time-to-live
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fields in the
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.Tn IP
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header for
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.Dv SOCK_STREAM , SOCK_DGRAM ,
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and certain types of
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.Dv SOCK_RAW
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sockets.
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For example,
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.Bd -literal
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int tos = IPTOS_LOWDELAY; /* see <netinet/ip.h> */
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setsockopt(s, IPPROTO_IP, IP_TOS, &tos, sizeof(tos));
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int ttl = 60; /* max = 255 */
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setsockopt(s, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
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.Ed
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.Pp
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If the
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.Dv IP_RECVDSTADDR
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option is enabled on a
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.Dv SOCK_DGRAM
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socket,
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the
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.Xr recvmsg 2
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call will return the destination
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.Tn IP
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address for a
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.Tn UDP
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datagram.
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The msg_control field in the msghdr structure points to a buffer
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that contains a cmsghdr structure followed by the
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.Tn IP
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address.
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The cmsghdr fields have the following values:
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.Bd -literal
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cmsg_len = sizeof(struct in_addr)
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cmsg_level = IPPROTO_IP
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cmsg_type = IP_RECVDSTADDR
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.Ed
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.Pp
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The source address to be used for outgoing
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.Tn UDP
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datagrams on a socket that is not bound to a specific
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.Tn IP
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address can be specified as ancillary data with a type code of
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.Dv IP_SENDSRCADDR .
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The msg_control field in the msghdr structure should point to a buffer
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that contains a cmsghdr structure followed by the
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.Tn IP
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address.
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The cmsghdr fields should have the following values:
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.Bd -literal
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cmsg_len = sizeof(struct in_addr)
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cmsg_level = IPPROTO_IP
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cmsg_type = IP_SENDSRCADDR
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.Ed
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.Pp
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For convenience,
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.Dv IP_SENDSRCADDR
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is defined to have the same value as
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.Dv IP_RECVDSTADDR ,
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so the
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.Dv IP_RECVDSTADDR
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control message from
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.Xr recvmsg 2
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can be used directly as a control message for
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.Xr sendmsg 2 .
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.Pp
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.Dv IP_PORTRANGE
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may be used to set the port range used for selecting a local port number
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on a socket with an unspecified (zero) port number.
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It has the following
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possible values:
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.Bl -tag -width IP_PORTRANGE_DEFAULT
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.It Dv IP_PORTRANGE_DEFAULT
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use the default range of values, normally
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.Dv IPPORT_HIFIRSTAUTO
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through
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.Dv IPPORT_HILASTAUTO .
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This is adjustable through the sysctl setting:
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.Sy net.inet.ip.portrange.first
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and
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.Sy net.inet.ip.portrange.last .
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.It Dv IP_PORTRANGE_HIGH
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use a high range of values, normally
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.Dv IPPORT_HIFIRSTAUTO
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and
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.Dv IPPORT_HILASTAUTO .
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This is adjustable through the sysctl setting:
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.Sy net.inet.ip.portrange.hifirst
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and
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.Sy net.inet.ip.portrange.hilast .
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.It Dv IP_PORTRANGE_LOW
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use a low range of ports, which are normally restricted to
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privileged processes on
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.Ux
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systems. The range is normally from
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.Dv IPPORT_RESERVED - 1
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down to
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.Li IPPORT_RESERVEDSTART
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in descending order.
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This is adjustable through the sysctl setting:
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.Sy net.inet.ip.portrange.lowfirst
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and
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.Sy net.inet.ip.portrange.lowlast .
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.El
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.Ss "Multicast Options"
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.Pp
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.Tn IP
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multicasting is supported only on
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.Dv AF_INET
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sockets of type
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.Dv SOCK_DGRAM
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and
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.Dv SOCK_RAW ,
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and only on networks where the interface
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driver supports multicasting.
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.Pp
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The
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.Dv IP_MULTICAST_TTL
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option changes the time-to-live (TTL)
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for outgoing multicast datagrams
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in order to control the scope of the multicasts:
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.Bd -literal
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u_char ttl; /* range: 0 to 255, default = 1 */
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setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
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.Ed
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.Pp
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Datagrams with a TTL of 1 are not forwarded beyond the local network.
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Multicast datagrams with a TTL of 0 will not be transmitted on any network,
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but may be delivered locally if the sending host belongs to the destination
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group and if multicast loopback has not been disabled on the sending socket
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(see below). Multicast datagrams with TTL greater than 1 may be forwarded
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to other networks if a multicast router is attached to the local network.
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.Pp
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For hosts with multiple interfaces, each multicast transmission is
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sent from the primary network interface.
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The
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.Dv IP_MULTICAST_IF
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option overrides the default for
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subsequent transmissions from a given socket:
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.Bd -literal
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struct in_addr addr;
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setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF, &addr, sizeof(addr));
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.Ed
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.Pp
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where "addr" is the local
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.Tn IP
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address of the desired interface or
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.Dv INADDR_ANY
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to specify the default interface.
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An interface's local IP address and multicast capability can
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be obtained via the
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.Dv SIOCGIFCONF
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and
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.Dv SIOCGIFFLAGS
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ioctls.
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Normal applications should not need to use this option.
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.Pp
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If a multicast datagram is sent to a group to which the sending host itself
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belongs (on the outgoing interface), a copy of the datagram is, by default,
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looped back by the IP layer for local delivery.
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The
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.Dv IP_MULTICAST_LOOP
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option gives the sender explicit control
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over whether or not subsequent datagrams are looped back:
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.Bd -literal
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u_char loop; /* 0 = disable, 1 = enable (default) */
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setsockopt(s, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop));
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.Ed
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.Pp
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This option
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improves performance for applications that may have no more than one
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instance on a single host (such as a router daemon), by eliminating
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the overhead of receiving their own transmissions. It should generally not
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be used by applications for which there may be more than one instance on a
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single host (such as a conferencing program) or for which the sender does
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not belong to the destination group (such as a time querying program).
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.Pp
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A multicast datagram sent with an initial TTL greater than 1 may be delivered
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to the sending host on a different interface from that on which it was sent,
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if the host belongs to the destination group on that other interface. The
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loopback control option has no effect on such delivery.
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.Pp
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A host must become a member of a multicast group before it can receive
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datagrams sent to the group. To join a multicast group, use the
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.Dv IP_ADD_MEMBERSHIP
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option:
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.Bd -literal
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struct ip_mreq mreq;
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setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));
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.Ed
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.Pp
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where
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.Fa mreq
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is the following structure:
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.Bd -literal
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struct ip_mreq {
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struct in_addr imr_multiaddr; /* IP multicast address of group */
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struct in_addr imr_interface; /* local IP address of interface */
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}
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.Ed
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.Pp
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.Dv imr_interface
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should
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be
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.Dv INADDR_ANY
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to choose the default multicast interface,
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or the
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.Tn IP
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address of a particular multicast-capable interface if
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the host is multihomed.
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Membership is associated with a single interface;
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programs running on multihomed hosts may need to
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join the same group on more than one interface.
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Up to
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.Dv IP_MAX_MEMBERSHIPS
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(currently 20) memberships may be added on a
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single socket.
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.Pp
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To drop a membership, use:
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.Bd -literal
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struct ip_mreq mreq;
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setsockopt(s, IPPROTO_IP, IP_DROP_MEMBERSHIP, &mreq, sizeof(mreq));
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.Ed
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.Pp
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where
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.Fa mreq
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contains the same values as used to add the membership.
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Memberships are dropped when the socket is closed or the process exits.
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.\"-----------------------
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.Ss "Raw IP Sockets"
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.Pp
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Raw
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.Tn IP
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sockets are connectionless,
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and are normally used with the
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.Xr sendto 2
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and
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.Xr recvfrom 2
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calls, though the
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.Xr connect 2
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call may also be used to fix the destination for future
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packets (in which case the
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.Xr read 2
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or
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.Xr recv 2
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and
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.Xr write 2
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or
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.Xr send 2
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system calls may be used).
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.Pp
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If
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.Fa proto
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is 0, the default protocol
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.Dv IPPROTO_RAW
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is used for outgoing
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packets, and only incoming packets destined for that protocol
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are received.
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If
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.Fa proto
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is non-zero, that protocol number will be used on outgoing packets
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and to filter incoming packets.
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.Pp
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Outgoing packets automatically have an
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.Tn IP
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header prepended to
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them (based on the destination address and the protocol
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number the socket is created with),
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unless the
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.Dv IP_HDRINCL
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option has been set.
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Incoming packets are received with
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.Tn IP
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header and options intact.
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.Pp
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.Dv IP_HDRINCL
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indicates the complete IP header is included with the data
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and may be used only with the
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.Dv SOCK_RAW
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type.
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.Bd -literal
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#include <netinet/in_systm.h>
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#include <netinet/ip.h>
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int hincl = 1; /* 1 = on, 0 = off */
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setsockopt(s, IPPROTO_IP, IP_HDRINCL, &hincl, sizeof(hincl));
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.Ed
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.Pp
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Unlike previous
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.Bx
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releases, the program must set all
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the fields of the IP header, including the following:
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.Bd -literal
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ip->ip_v = IPVERSION;
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ip->ip_hl = hlen >> 2;
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ip->ip_id = 0; /* 0 means kernel set appropriate value */
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ip->ip_off = offset;
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.Ed
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.Pp
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If the header source address is set to
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.Dv INADDR_ANY ,
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the kernel will choose an appropriate address.
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.Sh ERRORS
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A socket operation may fail with one of the following errors returned:
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.Bl -tag -width Er
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.It Bq Er EISCONN
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when trying to establish a connection on a socket which
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already has one, or when trying to send a datagram with the destination
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address specified and the socket is already connected;
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.It Bq Er ENOTCONN
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when trying to send a datagram, but
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no destination address is specified, and the socket hasn't been
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connected;
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.It Bq Er ENOBUFS
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when the system runs out of memory for
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an internal data structure;
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.It Bq Er EADDRNOTAVAIL
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when an attempt is made to create a
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socket with a network address for which no network interface
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exists.
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.It Bq Er EACCES
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when an attempt is made to create
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a raw IP socket by a non-privileged process.
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.El
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.Pp
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The following errors specific to
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.Tn IP
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may occur when setting or getting
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.Tn IP
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options:
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.Bl -tag -width EADDRNOTAVAILxx
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.It Bq Er EINVAL
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An unknown socket option name was given.
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.It Bq Er EINVAL
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The IP option field was improperly formed;
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an option field was shorter than the minimum value
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or longer than the option buffer provided.
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.El
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.Sh SEE ALSO
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.Xr getsockopt 2 ,
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.Xr recv 2 ,
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.Xr send 2 ,
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.Xr icmp 4 ,
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.Xr inet 4 ,
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.Xr intro 4
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.Sh HISTORY
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The
|
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.Nm
|
|
protocol appeared in
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|
.Bx 4.2 .
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