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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 60and 61.Tn i386 62these are word and byte reversed). 63The include file 64.In netinet/in.h 65defines this address 66as a discriminated union. 67.Pp 68Sockets bound to the Internet protocol family utilize 69the following addressing structure, 70.Bd -literal -offset indent 71struct sockaddr_in { 72 uint8_t sin_len; 73 sa_family_t sin_family; 74 in_port_t sin_port; 75 struct in_addr sin_addr; 76 char sin_zero[8]; 77}; 78.Ed 79.Pp 80Sockets may be created with the local address 81.Dv INADDR_ANY 82to affect 83.Dq wildcard 84matching on incoming messages. 85The address in a 86.Xr connect 2 87or 88.Xr sendto 2 89call may be given as 90.Dv INADDR_ANY 91to mean 92.Dq this host . 93The distinguished address 94.Dv INADDR_BROADCAST 95is allowed as a shorthand for the broadcast address on the primary 96network if the first network configured supports broadcast. 97.Sh PROTOCOLS 98The Internet protocol family is comprised of 99the 100.Tn IP 101network protocol, Internet Control 102Message Protocol 103.Pq Tn ICMP , 104Internet Group Management Protocol 105.Pq Tn IGMP , 106Transmission Control 107Protocol 108.Pq Tn TCP , 109and User Datagram Protocol 110.Pq Tn UDP . 111.Tn TCP 112is used to support the 113.Dv SOCK_STREAM 114abstraction while 115.Tn UDP 116is used to support the 117.Dv SOCK_DGRAM 118abstraction. 119A raw interface to 120.Tn IP 121is available 122by creating an Internet socket of type 123.Dv SOCK_RAW . 124The 125.Tn ICMP 126message protocol is accessible from a raw socket. 127.Pp 128The 129.Nm 130address on an interface consist of the address itself, the 131netmask, either broadcast address in case of a broadcast 132interface or peers address in case of point-to-point interface. 133The following 134.Xr ioctl 2 135commands are provided for a datagram socket in the Internet domain: 136.Pp 137.Bl -tag -width ".Dv SIOCGIFBRDADDR" -offset indent -compact 138.It Dv SIOCAIFADDR 139Add address to an interface. 140The command requires 141.Ft struct in_aliasreq 142as argument. 143.It Dv SIOCDIFADDR 144Delete address from an interface. 145The command requires 146.Ft struct ifreq 147as argument. 148.It Dv SIOCGIFADDR 149.It Dv SIOCGIFBRDADDR 150.It Dv SIOCGIFDSTADDR 151.It Dv SIOCGIFNETMASK 152Return address information from interface. The returned value 153is in 154.Ft struct ifreq . 155This way of address information retrieval is obsoleted, a 156preferred way is to use 157.Xr getifaddrs 3 158API. 159.El 160.Ss MIB Variables 161A number of variables are implemented in the net.inet branch of the 162.Xr sysctl 3 163MIB. 164In addition to the variables supported by the transport protocols 165(for which the respective manual pages may be consulted), 166the following general variables are defined: 167.Bl -tag -width IPCTL_FASTFORWARDING 168.It Dv IPCTL_FORWARDING 169.Pq ip.forwarding 170Boolean: enable/disable forwarding of IP packets. 171Defaults to off. 172.It Dv IPCTL_FASTFORWARDING 173.Pq ip.fastforwarding 174Boolean: enable/disable the use of 175.Tn fast IP forwarding 176code. 177Defaults to off. 178When 179.Tn fast IP forwarding 180is enabled, IP packets are forwarded directly to the appropriate network 181interface with direct processing to completion, which greatly improves 182the throughput. 183All packets for local IP addresses, non-unicast, or with IP options are 184handled by the normal IP input processing path. 185All features of the normal (slow) IP forwarding path are supported 186including firewall (through 187.Xr pfil 9 188hooks) checking, except 189.Xr ipsec 4 190tunnel brokering. 191The 192.Tn IP fastforwarding 193path does not generate ICMP redirect or source quench messages. 194.It Dv IPCTL_SENDREDIRECTS 195.Pq ip.redirect 196Boolean: enable/disable sending of ICMP redirects in response to 197.Tn IP 198packets for which a better, and for the sender directly reachable, route 199and next hop is known. 200Defaults to on. 201.It Dv IPCTL_DEFTTL 202.Pq ip.ttl 203Integer: default time-to-live 204.Pq Dq TTL 205to use for outgoing 206.Tn IP 207packets. 208.It Dv IPCTL_ACCEPTSOURCEROUTE 209.Pq ip.accept_sourceroute 210Boolean: enable/disable accepting of source-routed IP packets (default false). 211.It Dv IPCTL_SOURCEROUTE 212.Pq ip.sourceroute 213Boolean: enable/disable forwarding of source-routed IP packets (default false). 214.It Dv IPCTL_RTEXPIRE 215.Pq ip.rtexpire 216Integer: lifetime in seconds of protocol-cloned 217.Tn IP 218routes after the last reference drops (default one hour). 219This value varies dynamically as described above. 220.It Dv IPCTL_RTMINEXPIRE 221.Pq ip.rtminexpire 222Integer: minimum value of ip.rtexpire (default ten seconds). 223This value has no effect on user modifications, but restricts the dynamic 224adaptation described above. 225.It Dv IPCTL_RTMAXCACHE 226.Pq ip.rtmaxcache 227Integer: trigger level of cached, unreferenced, protocol-cloned routes 228which initiates dynamic adaptation (default 128). 229.It Va ip.process_options 230Integer: control IP options processing. 231By setting this variable to 0, all IP options in the incoming packets 232will be ignored, and the packets will be passed unmodified. 233By setting to 1, IP options in the incoming packets will be processed 234accordingly. 235By setting to 2, an 236.Tn ICMP 237.Dq "prohibited by filter" 238message will be sent back in response to incoming packets with IP options. 239Default is 1. 240This 241.Xr sysctl 8 242variable affects packets destined for a local host as well as packets 243forwarded to some other host. 244.It Va ip.random_id 245Boolean: control IP IDs generation behaviour. 246Setting this 247.Xr sysctl 8 248to non-zero causes the ID field in IP packets to be randomized instead of 249incremented by 1 with each packet generated. 250This closes a minor information leak which allows remote observers to 251determine the rate of packet generation on the machine by watching the 252counter. 253In the same time, on high-speed links, it can decrease the ID reuse 254cycle greatly. 255Default is 0 (sequential IP IDs). 256IPv6 flow IDs and fragment IDs are always random. 257.It Va ip.maxfragpackets 258Integer: maximum number of fragmented packets the host will accept and hold 259in the reassembling queue simultaneously. 2600 means that the host will not accept any fragmented packets. 261\-1 means that the host will accept as many fragmented packets as it receives. 262.It Va ip.maxfragsperpacket 263Integer: maximum number of fragments the host will accept and hold 264in the reassembling queue for a packet. 2650 means that the host will not accept any fragmented packets. 266.El 267.Sh SEE ALSO 268.Xr ioctl 2 , 269.Xr socket 2 , 270.Xr getifaddrs 3 , 271.Xr sysctl 3 , 272.Xr icmp 4 , 273.Xr intro 4 , 274.Xr ip 4 , 275.Xr ipfirewall 4 , 276.Xr route 4 , 277.Xr tcp 4 , 278.Xr udp 4 , 279.Xr pfil 9 280.Rs 281.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 282.%B PS1 283.%N 7 284.Re 285.Rs 286.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 287.%B PS1 288.%N 8 289.Re 290.Sh HISTORY 291The 292.Nm 293protocol interface appeared in 294.Bx 4.2 . 295The 296.Dq protocol cloning 297code appeared in 298.Fx 2.1 . 299.Sh CAVEATS 300The Internet protocol support is subject to change as 301the Internet protocols develop. 302Users should not depend 303on details of the current implementation, but rather 304the services exported. 305