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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: src/share/man/man4/inet.4,v 1.11.2.6 2001/12/17 11:30:12 ru Exp $ 30.\" 31.Dd March 22, 2015 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 the 58.Tn VAX 59these are word and byte reversed). 60The include file 61.In netinet/in.h 62defines this address 63as a discriminated union. 64.Pp 65Sockets bound to the Internet protocol family utilize 66the following addressing structure, 67.Bd -literal -offset indent 68struct sockaddr_in { 69 u_char sin_len; 70 sa_family_t sin_family; 71 u_short sin_port; 72 struct in_addr sin_addr; 73 char sin_zero[8]; 74}; 75.Ed 76.Pp 77Sockets may be created with the local address 78.Dv INADDR_ANY 79to affect 80.Dq wildcard 81matching on incoming messages. 82The address in a 83.Xr connect 2 84or 85.Xr sendto 2 86call may be given as 87.Dv INADDR_ANY 88to mean 89.Dq this host . 90The distinguished address 91.Dv INADDR_BROADCAST 92is allowed as a shorthand for the broadcast address on the primary 93network if the first network configured supports broadcast. 94.Sh PROTOCOLS 95The Internet protocol family is comprised of 96the 97.Tn IP 98network protocol, Internet Control 99Message Protocol 100.Pq Tn ICMP , 101Internet Group Management Protocol 102.Pq Tn IGMP , 103Transmission Control 104Protocol 105.Pq Tn TCP , 106and User Datagram Protocol 107.Pq Tn UDP . 108.Tn TCP 109is used to support the 110.Dv SOCK_STREAM 111abstraction while 112.Tn UDP 113is used to support the 114.Dv SOCK_DGRAM 115abstraction. 116A raw interface to 117.Tn IP 118is available 119by creating an Internet socket of type 120.Dv SOCK_RAW . 121The 122.Tn ICMP 123message protocol is accessible from a raw socket. 124.Pp 125The 32-bit Internet address contains both network and host parts. 126However, direct examination of addresses is discouraged. 127For those 128programs which absolutely need to break addresses into their component 129parts, the following 130.Xr ioctl 2 131commands are provided for a datagram socket in the Internet domain; 132they have the same form as the 133.Dv SIOCSIFADDR 134and 135.Dv SIOCGIFADDR 136commands (see 137.Xr intro 4 ) . 138.Bl -tag -width ".Dv SIOCSIFNETMASK" 139.It Dv SIOCSIFNETMASK 140Set interface network mask. 141The network mask defines the network part of the address; 142if it contains more of the address than the address type would indicate, 143then subnets are in use. 144.It Dv SIOCGIFNETMASK 145Get interface network mask. 146.El 147.Sh ROUTING 148The current implementation of Internet protocols includes some routing-table 149adaptations to provide enhanced caching of certain end-to-end 150information necessary for Transaction TCP and Path MTU Discovery. 151The following changes are the most significant: 152.Bl -enum 153.It 154All IP routes, except those with the 155.Dv RTF_CLONING 156flag and those to multicast destinations, have the 157.Dv RTF_PRCLONING 158flag forcibly enabled (they are thus said to be 159.Dq "protocol cloning" ) . 160.It 161When the last reference to an IP route is dropped, the route is 162examined to determine if it was created by cloning such a route. 163If this is the case, the 164.Dv RTF_PROTO3 165flag is turned on, and the expiration timer is initialized to go off in 166.Va net.inet.ip.rtexpire 167seconds. 168If such a route is re-referenced, the 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 176.Va net.inet.ip.rtexpire 177if the number of cached routes grows too large. 178If after an expiration run there are still more than 179.Va net.inet.ip.rtmaxcache 180unreferenced routes remaining, the rtexpire 181value is multiplied by \(34, and any routes which have longer 182expiration times have those times adjusted. 183This process is damped somewhat by specification of a minimum rtexpire value 184.Va ( net.inet.ip.rtminexpire ) , 185and by restricting the reduction to once in a ten-minute period. 186.Pp 187If some external process deletes the original route from which a 188protocol-cloned route was generated, the ``child route'' is deleted. 189(This is actually a generic mechanism in the routing code support for 190protocol-requested cloning.) 191.Pp 192No attempt is made to manage routes which were not created by protocol 193cloning; these are assumed to be static, under the management of an 194external routing process, or under the management of a link layer 195(e.g., 196.Tn ARP 197for Ethernets). 198.Pp 199Only certain types of network activity will result in the cloning of a 200route using this mechanism. 201Specifically, those protocols (such as 202.Tn TCP 203and 204.Tn UDP ) 205which themselves cache a long-lasting reference to route for a destination 206will trigger the mechanism; whereas raw 207.Tn IP 208packets, whether locally-generated or forwarded, will not. 209.Ss MIB Variables 210A number of variables are implemented in the net.inet branch of the 211.Xr sysctl 3 212MIB. 213In addition to the variables supported by the transport protocols 214(for which the respective manual pages may be consulted), 215the following general variables are defined: 216.Bl -tag -width IPCTL_FASTFORWARDING 217.It Dv IPCTL_FORWARDING 218.Pq ip.forwarding 219Boolean: enable/disable forwarding of IP packets. 220Defaults to off. 221.It Dv IPCTL_FASTFORWARDING 222.Pq ip.fastforwarding 223Boolean: enable/disable the use of fast IP forwarding code. 224Defaults to off. 225When fast forwarding is enabled, IP packets are forwarded directly to 226the appropriate network interface with a minimal validity checking, which 227greatly improves the throughput. 228On the other hand, they bypass the 229standard procedures, such as IP option processing and 230.Xr ipfirewall 4 231checking. 232It is not guaranteed that every packet will be fast-forwarded. 233.It Dv IPCTL_SENDREDIRECTS 234.Pq ip.redirect 235Boolean: enable/disable sending of ICMP redirects in response to 236unforwardable 237.Tn IP 238packets. 239Defaults to on. 240.It Dv IPCTL_DEFTTL 241.Pq ip.ttl 242Integer: default time-to-live 243.Pq Dq TTL 244to use for outgoing 245.Tn IP 246packets. 247.It Dv IPCTL_SOURCEROUTE 248.Pq ip.sourceroute 249Boolean: enable/disable forwarding of source-routed IP packets (default false). 250.It Dv IPCTL_RTEXPIRE 251.Pq ip.rtexpire 252Integer: lifetime in seconds of protocol-cloned 253.Tn IP 254routes after the last reference drops (default one hour). 255This value varies dynamically as described above. 256.It Dv IPCTL_RTMINEXPIRE 257.Pq ip.rtminexpire 258Integer: minimum value of ip.rtexpire (default ten seconds). 259This value has no effect on user modifications, but restricts the dynamic 260adaptation described above. 261.It Dv IPCTL_RTMAXCACHE 262.Pq ip.rtmaxcache 263Integer: trigger level of cached, unreferenced, protocol-cloned routes 264which initiates dynamic adaptation (default 128). 265.El 266.Sh SEE ALSO 267.Xr ioctl 2 , 268.Xr socket 2 , 269.Xr sysctl 3 , 270.Xr icmp 4 , 271.Xr intro 4 , 272.Xr ip 4 , 273.Xr ipfirewall 4 , 274.Xr tcp 4 , 275.Xr udp 4 276.Rs 277.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 278.%B PS1 279.%N 7 280.Re 281.Rs 282.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 283.%B PS1 284.%N 8 285.Re 286.Sh CAVEATS 287The Internet protocol support is subject to change as 288the Internet protocols develop. 289Users should not depend on details of the current implementation, but rather 290the services exported. 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