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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: src/share/man/man4/inet.4,v 1.11.2.6 2001/12/17 11:30:12 ru Exp $ 34.\" 35.Dd February 14, 1995 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 the 62.Tn VAX 63these are word and byte 64reversed). The include file 65.Aq Pa 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 u_char sin_len; 74 u_char sin_family; 75 u_short 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. A 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 32-bit Internet address contains both network and host parts. 129However, direct examination of addresses is discouraged. For those 130programs which absolutely need to break addresses into their component 131parts, the following 132.Xr ioctl 2 133commands are provided for a datagram socket in the Internet domain; 134they have the same form as the 135.Dv SIOCIFADDR 136command (see 137.Xr intro 4 ) . 138.Pp 139.Bl -tag -width SIOCSIFNETMASK 140.It Dv SIOCSIFNETMASK 141Set interface network mask. 142The network mask defines the network part of the address; 143if it contains more of the address than the address type would indicate, 144then subnets are in use. 145.It Dv SIOCGIFNETMASK 146Get interface network mask. 147.El 148.Sh ROUTING 149The current implementation of Internet protocols includes some routing-table 150adaptations to provide enhanced caching of certain end-to-end 151information necessary for Transaction TCP and Path MTU Discovery. The 152following changes are the most significant: 153.Bl -enum 154.It 155All IP routes, except those with the 156.Dv RTF_CLONING 157flag and those to multicast destinations, have the 158.Dv RTF_PRCLONING 159flag forcibly enabled (they are thus said to be 160.Dq "protocol cloning" ) . 161.It 162When the last reference to an IP route is dropped, the route is 163examined to determine if it was created by cloning such a route. If 164this is the case, the 165.Dv RTF_PROTO3 166flag is turned on, and the expiration timer is initialized to go off 167in net.inet.ip.rtexpire seconds. If such a route is re-referenced, 168the flag and expiration timer are reset. 169.It 170A kernel timeout runs once every ten minutes, or sooner if there are 171soon-to-expire routes in the kernel routing table, and deletes the 172expired routes. 173.El 174.Pp 175A dynamic process is in place to modify the value of 176net.inet.ip.rtexpire if the number of cached routes grows too large. 177If after an expiration run there are still more than 178net.inet.ip.rtmaxcache unreferenced routes remaining, the rtexpire 179value is multiplied by 3/4, and any routes which have longer 180expiration times have those times adjusted. This process is damped 181somewhat by specification of a minimum rtexpire value 182(net.inet.ip.rtminexpire), and by restricting the reduction to once in 183a ten-minute period. 184.Pp 185If some external process deletes the original route from which a 186protocol-cloned route was generated, the ``child route'' is deleted. 187(This is actually a generic mechanism in the routing code support for 188protocol-requested cloning.) 189.Pp 190No attempt is made to manage routes which were not created by protocol 191cloning; these are assumed to be static, under the management of an 192external routing process, or under the management of a link layer 193(e.g., 194.Tn ARP 195for Ethernets). 196.Pp 197Only certain types of network activity will result in the cloning of a 198route using this mechanism. Specifically, those protocols (such as 199.Tn TCP 200and 201.Tn UDP ) 202which themselves cache a long-lasting reference to route for a destination 203will trigger the mechanism; whereas raw 204.Tn IP 205packets, whether locally-generated or forwarded, will not. 206.Ss MIB Variables 207A number of variables are implemented in the net.inet branch of the 208.Xr sysctl 3 209MIB. 210In addition to the variables supported by the transport protocols 211(for which the respective manual pages may be consulted), 212the following general variables are defined: 213.Bl -tag -width IPCTL_FASTFORWARDING 214.It Dv IPCTL_FORWARDING 215.Pq ip.forwarding 216Boolean: enable/disable forwarding of IP packets. 217Defaults to off. 218.It Dv IPCTL_FASTFORWARDING 219.Pq ip.fastforwarding 220Boolean: enable/disable the use of fast IP forwarding code. 221Defaults to off. 222When fast forwarding is enabled, IP packets are forwarded directly to 223the appropriate network interface with a minimal validity checking, which 224greatly improves the throughput. On the other hand, they bypass the 225standard procedures, such as IP option processing and 226.Xr ipfirewall 4 227checking. 228It is not guaranteed that every packet will be fast-forwarded. 229.It Dv IPCTL_SENDREDIRECTS 230.Pq ip.redirect 231Boolean: enable/disable sending of ICMP redirects in response to 232unforwardable 233.Tn IP 234packets. 235Defaults to on. 236.It Dv IPCTL_DEFTTL 237.Pq ip.ttl 238Integer: default time-to-live 239.Pq Dq TTL 240to use for outgoing 241.Tn IP 242packets. 243.It Dv IPCTL_SOURCEROUTE 244.Pq ip.sourceroute 245Boolean: enable/disable forwarding of source-routed IP packets (default false). 246.It Dv IPCTL_RTEXPIRE 247.Pq ip.rtexpire 248Integer: lifetime in seconds of protocol-cloned 249.Tn IP 250routes after the last reference drops (default one hour). This value 251varies dynamically as described above. 252.It Dv IPCTL_RTMINEXPIRE 253.Pq ip.rtminexpire 254Integer: minimum value of ip.rtexpire (default ten seconds). This 255value has no effect on user modifications, but restricts the dynamic 256adaptation described above. 257.It Dv IPCTL_RTMAXCACHE 258.Pq ip.rtmaxcache 259Integer: trigger level of cached, unreferenced, protocol-cloned routes 260which initiates dynamic adaptation (default 128). 261.El 262.Sh SEE ALSO 263.Xr ioctl 2 , 264.Xr socket 2 , 265.Xr sysctl 3 , 266.Xr icmp 4 , 267.Xr intro 4 , 268.Xr ip 4 , 269.Xr ipfirewall 4 , 270.Xr tcp 4 , 271.Xr ttcp 4 , 272.Xr udp 4 273.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 CAVEAT 284The Internet protocol support is subject to change as 285the Internet protocols develop. Users should not depend 286on details of the current implementation, but rather 287the services exported. 288.Sh HISTORY 289The 290.Nm 291protocol interface appeared in 292.Bx 4.2 . 293The 294.Dq protocol cloning 295code appeared in 296.Fx 2.1 . 297