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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" From: @(#)inet.4 8.1 (Berkeley) 6/5/93 29.\" $FreeBSD$ 30.\" 31.Dd January 26, 2012 32.Dt INET 4 33.Os 34.Sh NAME 35.Nm inet 36.Nd Internet protocol family 37.Sh SYNOPSIS 38.In sys/types.h 39.In netinet/in.h 40.Sh DESCRIPTION 41The Internet protocol family is a collection of protocols 42layered atop the 43.Em Internet Protocol 44.Pq Tn IP 45transport layer, and utilizing the Internet address format. 46The Internet family provides protocol support for the 47.Dv SOCK_STREAM , SOCK_DGRAM , 48and 49.Dv SOCK_RAW 50socket types; the 51.Dv SOCK_RAW 52interface provides access to the 53.Tn IP 54protocol. 55.Sh ADDRESSING 56Internet addresses are four byte quantities, stored in 57network standard format (on little endian machines, such as the 58.Tn alpha , 59.Tn amd64 , 60.Tn i386 61and 62.Tn ia64 63these are word and byte reversed). 64The include file 65.In netinet/in.h 66defines this address 67as a discriminated union. 68.Pp 69Sockets bound to the Internet protocol family utilize 70the following addressing structure, 71.Bd -literal -offset indent 72struct sockaddr_in { 73 uint8_t sin_len; 74 sa_family_t sin_family; 75 in_port_t sin_port; 76 struct in_addr sin_addr; 77 char sin_zero[8]; 78}; 79.Ed 80.Pp 81Sockets may be created with the local address 82.Dv INADDR_ANY 83to affect 84.Dq wildcard 85matching on incoming messages. 86The address in a 87.Xr connect 2 88or 89.Xr sendto 2 90call may be given as 91.Dv INADDR_ANY 92to mean 93.Dq this host . 94The distinguished address 95.Dv INADDR_BROADCAST 96is allowed as a shorthand for the broadcast address on the primary 97network if the first network configured supports broadcast. 98.Sh PROTOCOLS 99The Internet protocol family is comprised of 100the 101.Tn IP 102network protocol, Internet Control 103Message Protocol 104.Pq Tn ICMP , 105Internet Group Management Protocol 106.Pq Tn IGMP , 107Transmission Control 108Protocol 109.Pq Tn TCP , 110and User Datagram Protocol 111.Pq Tn UDP . 112.Tn TCP 113is used to support the 114.Dv SOCK_STREAM 115abstraction while 116.Tn UDP 117is used to support the 118.Dv SOCK_DGRAM 119abstraction. 120A raw interface to 121.Tn IP 122is available 123by creating an Internet socket of type 124.Dv SOCK_RAW . 125The 126.Tn ICMP 127message protocol is accessible from a raw socket. 128.Pp 129The 130.Nm 131address on an interface consist of the address itself, the 132netmask, either broadcast address in case of a broadcast 133interface or peers address in case of point-to-point interface. 134The following 135.Xr ioctl 2 136commands are provided for a datagram socket in the Internet domain: 137.Pp 138.Bl -tag -width ".Dv SIOCGIFBRDADDR" -offset indent -compact 139.It Dv SIOCAIFADDR 140Add address to an interface. 141The command requires 142.Ft struct in_aliasreq 143as argument. 144.It Dv SIOCDIFADDR 145Delete address from an interface. 146The command requires 147.Ft struct ifreq 148as argument. 149.It Dv SIOCGIFADDR 150.It Dv SIOCGIFBRDADDR 151.It Dv SIOCGIFDSTADDR 152.It Dv SIOCGIFNETMASK 153Return address information from interface. The returned value 154is in 155.Ft struct ifreq . 156This way of address information retrieval is obsoleted, a 157preferred way is to use 158.Xr getifaddrs 3 159API. 160.El 161.Ss MIB Variables 162A number of variables are implemented in the net.inet branch of the 163.Xr sysctl 3 164MIB. 165In addition to the variables supported by the transport protocols 166(for which the respective manual pages may be consulted), 167the following general variables are defined: 168.Bl -tag -width IPCTL_FASTFORWARDING 169.It Dv IPCTL_FORWARDING 170.Pq ip.forwarding 171Boolean: enable/disable forwarding of IP packets. 172Defaults to off. 173.It Dv IPCTL_FASTFORWARDING 174.Pq ip.fastforwarding 175Boolean: enable/disable the use of 176.Tn fast IP forwarding 177code. 178Defaults to off. 179When 180.Tn fast IP forwarding 181is enabled, IP packets are forwarded directly to the appropriate network 182interface with direct processing to completion, which greatly improves 183the throughput. 184All packets for local IP addresses, non-unicast, or with IP options are 185handled by the normal IP input processing path. 186All features of the normal (slow) IP forwarding path are supported 187including firewall (through 188.Xr pfil 9 189hooks) checking, except 190.Xr ipsec 4 191tunnel brokering. 192The 193.Tn IP fastforwarding 194path does not generate ICMP redirect or source quench messages. 195.It Dv IPCTL_SENDREDIRECTS 196.Pq ip.redirect 197Boolean: enable/disable sending of ICMP redirects in response to 198.Tn IP 199packets for which a better, and for the sender directly reachable, route 200and next hop is known. 201Defaults to on. 202.It Dv IPCTL_DEFTTL 203.Pq ip.ttl 204Integer: default time-to-live 205.Pq Dq TTL 206to use for outgoing 207.Tn IP 208packets. 209.It Dv IPCTL_ACCEPTSOURCEROUTE 210.Pq ip.accept_sourceroute 211Boolean: enable/disable accepting of source-routed IP packets (default false). 212.It Dv IPCTL_SOURCEROUTE 213.Pq ip.sourceroute 214Boolean: enable/disable forwarding of source-routed IP packets (default false). 215.It Dv IPCTL_RTEXPIRE 216.Pq ip.rtexpire 217Integer: lifetime in seconds of protocol-cloned 218.Tn IP 219routes after the last reference drops (default one hour). 220This value varies dynamically as described above. 221.It Dv IPCTL_RTMINEXPIRE 222.Pq ip.rtminexpire 223Integer: minimum value of ip.rtexpire (default ten seconds). 224This value has no effect on user modifications, but restricts the dynamic 225adaptation described above. 226.It Dv IPCTL_RTMAXCACHE 227.Pq ip.rtmaxcache 228Integer: trigger level of cached, unreferenced, protocol-cloned routes 229which initiates dynamic adaptation (default 128). 230.It Va ip.process_options 231Integer: control IP options processing. 232By setting this variable to 0, all IP options in the incoming packets 233will be ignored, and the packets will be passed unmodified. 234By setting to 1, IP options in the incoming packets will be processed 235accordingly. 236By setting to 2, an 237.Tn ICMP 238.Dq "prohibited by filter" 239message will be sent back in response to incoming packets with IP options. 240Default is 1. 241This 242.Xr sysctl 8 243variable affects packets destined for a local host as well as packets 244forwarded to some other host. 245.It Va ip.random_id 246Boolean: control IP IDs generation behaviour. 247Setting this 248.Xr sysctl 8 249to non-zero causes the ID field in IP packets to be randomized instead of 250incremented by 1 with each packet generated. 251This closes a minor information leak which allows remote observers to 252determine the rate of packet generation on the machine by watching the 253counter. 254In the same time, on high-speed links, it can decrease the ID reuse 255cycle greatly. 256Default is 0 (sequential IP IDs). 257IPv6 flow IDs and fragment IDs are always random. 258.It Va ip.maxfragpackets 259Integer: maximum number of fragmented packets the host will accept and hold 260in the reassembling queue simultaneously. 2610 means that the host will not accept any fragmented packets. 262\-1 means that the host will accept as many fragmented packets as it receives. 263.It Va ip.maxfragsperpacket 264Integer: maximum number of fragments the host will accept and hold 265in the reassembling queue for a packet. 2660 means that the host will not accept any fragmented packets. 267.El 268.Sh SEE ALSO 269.Xr ioctl 2 , 270.Xr socket 2 , 271.Xr getifaddrs 3 , 272.Xr sysctl 3 , 273.Xr icmp 4 , 274.Xr intro 4 , 275.Xr ip 4 , 276.Xr ipfirewall 4 , 277.Xr route 4 , 278.Xr tcp 4 , 279.Xr udp 4 , 280.Xr pfil 9 281.Rs 282.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 283.%B PS1 284.%N 7 285.Re 286.Rs 287.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 288.%B PS1 289.%N 8 290.Re 291.Sh HISTORY 292The 293.Nm 294protocol interface appeared in 295.Bx 4.2 . 296The 297.Dq protocol cloning 298code appeared in 299.Fx 2.1 . 300.Sh CAVEATS 301The Internet protocol support is subject to change as 302the Internet protocols develop. 303Users should not depend 304on details of the current implementation, but rather 305the services exported. 306