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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.\" From: @(#)inet.4 8.1 (Berkeley) 6/5/93 33.\" $FreeBSD$ 34.\" 35.Dd April 9, 2005 36.Dt INET 4 37.Os 38.Sh NAME 39.Nm inet 40.Nd Internet protocol family 41.Sh SYNOPSIS 42.In sys/types.h 43.In netinet/in.h 44.Sh DESCRIPTION 45The Internet protocol family is a collection of protocols 46layered atop the 47.Em Internet Protocol 48.Pq Tn IP 49transport layer, and utilizing the Internet address format. 50The Internet family provides protocol support for the 51.Dv SOCK_STREAM , SOCK_DGRAM , 52and 53.Dv SOCK_RAW 54socket types; the 55.Dv SOCK_RAW 56interface provides access to the 57.Tn IP 58protocol. 59.Sh ADDRESSING 60Internet addresses are four byte quantities, stored in 61network standard format (on little endian machines, such as the 62.Tn alpha , 63.Tn amd64 , 64.Tn i386 65and 66.Tn ia64 67these are word and byte reversed). 68The include file 69.In netinet/in.h 70defines this address 71as a discriminated union. 72.Pp 73Sockets bound to the Internet protocol family utilize 74the following addressing structure, 75.Bd -literal -offset indent 76struct sockaddr_in { 77 uint8_t sin_len; 78 sa_family_t sin_family; 79 in_port_t sin_port; 80 struct in_addr sin_addr; 81 char sin_zero[8]; 82}; 83.Ed 84.Pp 85Sockets may be created with the local address 86.Dv INADDR_ANY 87to affect 88.Dq wildcard 89matching on incoming messages. 90The address in a 91.Xr connect 2 92or 93.Xr sendto 2 94call may be given as 95.Dv INADDR_ANY 96to mean 97.Dq this host . 98The distinguished address 99.Dv INADDR_BROADCAST 100is allowed as a shorthand for the broadcast address on the primary 101network if the first network configured supports broadcast. 102.Sh PROTOCOLS 103The Internet protocol family is comprised of 104the 105.Tn IP 106network protocol, Internet Control 107Message Protocol 108.Pq Tn ICMP , 109Internet Group Management Protocol 110.Pq Tn IGMP , 111Transmission Control 112Protocol 113.Pq Tn TCP , 114and User Datagram Protocol 115.Pq Tn UDP . 116.Tn TCP 117is used to support the 118.Dv SOCK_STREAM 119abstraction while 120.Tn UDP 121is used to support the 122.Dv SOCK_DGRAM 123abstraction. 124A raw interface to 125.Tn IP 126is available 127by creating an Internet socket of type 128.Dv SOCK_RAW . 129The 130.Tn ICMP 131message protocol is accessible from a raw socket. 132.Pp 133The 32-bit Internet address contains both network and host parts. 134However, direct examination of addresses is discouraged. 135For those 136programs which absolutely need to break addresses into their component 137parts, the following 138.Xr ioctl 2 139commands are provided for a datagram socket in the Internet domain; 140they have the same form as the 141.Dv SIOCIFADDR 142command (see 143.Xr intro 4 ) . 144.Pp 145.Bl -tag -width SIOCSIFNETMASK 146.It Dv SIOCSIFNETMASK 147Set interface network mask. 148The network mask defines the network part of the address; 149if it contains more of the address than the address type would indicate, 150then subnets are in use. 151.It Dv SIOCGIFNETMASK 152Get interface network mask. 153.El 154.Ss MIB Variables 155A number of variables are implemented in the net.inet branch of the 156.Xr sysctl 3 157MIB. 158In addition to the variables supported by the transport protocols 159(for which the respective manual pages may be consulted), 160the following general variables are defined: 161.Bl -tag -width IPCTL_FASTFORWARDING 162.It Dv IPCTL_FORWARDING 163.Pq ip.forwarding 164Boolean: enable/disable forwarding of IP packets. 165Defaults to off. 166.It Dv IPCTL_FASTFORWARDING 167.Pq ip.fastforwarding 168Boolean: enable/disable the use of 169.Tn fast IP forwarding 170code. 171Defaults to off. 172When 173.Tn fast IP forwarding 174is enabled, IP packets are forwarded directly to the appropriate network 175interface with direct processing to completion, which greatly improves 176the throughput. 177All packets for local IP addresses, non-unicast, or with IP options are 178handled by the normal IP input processing path. 179All features of the normal (slow) IP forwarding path are supported 180including firewall (through 181.Xr pfil 9 182hooks) checking, except 183.Xr ipsec 4 184tunnel brokering. 185The 186.Tn IP fastforwarding 187path does not generate ICMP redirect or source quench messages. 188.It Dv IPCTL_SENDREDIRECTS 189.Pq ip.redirect 190Boolean: enable/disable sending of ICMP redirects in response to 191.Tn IP 192packets for which a better, and for the sender directly reachable, route 193and next hop is known. 194Defaults to on. 195.It Dv IPCTL_DEFTTL 196.Pq ip.ttl 197Integer: default time-to-live 198.Pq Dq TTL 199to use for outgoing 200.Tn IP 201packets. 202.It Dv IPCTL_ACCEPTSOURCEROUTE 203.Pq ip.accept_sourceroute 204Boolean: enable/disable accepting of source-routed IP packets (default false). 205.It Dv IPCTL_SOURCEROUTE 206.Pq ip.sourceroute 207Boolean: enable/disable forwarding of source-routed IP packets (default false). 208.It Dv IPCTL_RTEXPIRE 209.Pq ip.rtexpire 210Integer: lifetime in seconds of protocol-cloned 211.Tn IP 212routes after the last reference drops (default one hour). 213This value varies dynamically as described above. 214.It Dv IPCTL_RTMINEXPIRE 215.Pq ip.rtminexpire 216Integer: minimum value of ip.rtexpire (default ten seconds). 217This value has no effect on user modifications, but restricts the dynamic 218adaptation described above. 219.It Dv IPCTL_RTMAXCACHE 220.Pq ip.rtmaxcache 221Integer: trigger level of cached, unreferenced, protocol-cloned routes 222which initiates dynamic adaptation (default 128). 223.It Va ip.process_options 224Integer: control IP options processing. 225By setting this variable to 0, all IP options in the incoming packets 226will be ignored, and the packets will be passed unmodified. 227By setting to 1, IP options in the incoming packets will be processed 228accordingly. 229By setting to 2, an 230.Tn ICMP 231.Dq "prohibited by filter" 232message will be sent back in response to incoming packets with IP options. 233Default is 1. 234This 235.Xr sysctl 8 236variable affects packets destined for a local host as well as packets 237forwarded to some other host. 238.It Va ip.random_id 239Boolean: control IP IDs generation behaviour. 240Setting this 241.Xr sysctl 8 242to non-zero causes the ID field in IP packets to be randomized instead of 243incremented by 1 with each packet generated. 244This closes a minor information leak which allows remote observers to 245determine the rate of packet generation on the machine by watching the 246counter. 247In the same time, on high-speed links, it can decrease the ID reuse 248cycle greatly. 249Default is 0 (sequential IP IDs). 250IPv6 flow IDs and fragment IDs are always random. 251.It Va ip.maxfragpackets 252Integer: maximum number of fragmented packets the host will accept and hold 253in the reassembling queue simultaneously. 2540 means that the host will not accept any fragmented packets. 255\-1 means that the host will accept as many fragmented packets as it receives. 256.It Va ip.maxfragsperpacket 257Integer: maximum number of fragments the host will accept and hold 258in the reassembling queue for a packet. 2590 means that the host will not accept any fragmented packets. 260.El 261.Sh SEE ALSO 262.Xr ioctl 2 , 263.Xr socket 2 , 264.Xr sysctl 3 , 265.Xr icmp 4 , 266.Xr intro 4 , 267.Xr ip 4 , 268.Xr ipfirewall 4 , 269.Xr route 4 , 270.Xr tcp 4 , 271.Xr udp 4 , 272.Xr pfil 9 273.Rs 274.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 275.%B PS1 276.%N 7 277.Re 278.Rs 279.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 280.%B PS1 281.%N 8 282.Re 283.Sh HISTORY 284The 285.Nm 286protocol interface appeared in 287.Bx 4.2 . 288The 289.Dq protocol cloning 290code appeared in 291.Fx 2.1 . 292.Sh CAVEATS 293The Internet protocol support is subject to change as 294the Internet protocols develop. 295Users should not depend 296on details of the current implementation, but rather 297the services exported. 298