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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.\" $DragonFly: src/share/man/man4/inet.4,v 1.8 2008/05/02 02:05:05 swildner Exp $ 31.\" 32.Dd February 14, 1995 33.Dt INET 4 34.Os 35.Sh NAME 36.Nm inet 37.Nd Internet protocol family 38.Sh SYNOPSIS 39.In sys/types.h 40.In netinet/in.h 41.Sh DESCRIPTION 42The Internet protocol family is a collection of protocols 43layered atop the 44.Em Internet Protocol 45.Pq Tn IP 46transport layer, and utilizing the Internet address format. 47The Internet family provides protocol support for the 48.Dv SOCK_STREAM , SOCK_DGRAM , 49and 50.Dv SOCK_RAW 51socket types; the 52.Dv SOCK_RAW 53interface provides access to the 54.Tn IP 55protocol. 56.Sh ADDRESSING 57Internet addresses are four byte quantities, stored in 58network standard format (on the 59.Tn VAX 60these are word and byte 61reversed). The include file 62.In netinet/in.h 63defines this address 64as a discriminated union. 65.Pp 66Sockets bound to the Internet protocol family utilize 67the following addressing structure, 68.Bd -literal -offset indent 69struct sockaddr_in { 70 u_char sin_len; 71 u_char sin_family; 72 u_short sin_port; 73 struct in_addr sin_addr; 74 char sin_zero[8]; 75}; 76.Ed 77.Pp 78Sockets may be created with the local address 79.Dv INADDR_ANY 80to affect 81.Dq wildcard 82matching on incoming messages. 83The address in a 84.Xr connect 2 85or 86.Xr sendto 2 87call may be given as 88.Dv INADDR_ANY 89to mean 90.Dq this host . 91The distinguished address 92.Dv INADDR_BROADCAST 93is allowed as a shorthand for the broadcast address on the primary 94network if the first network configured supports broadcast. 95.Sh PROTOCOLS 96The Internet protocol family is comprised of 97the 98.Tn IP 99network protocol, Internet Control 100Message Protocol 101.Pq Tn ICMP , 102Internet Group Management Protocol 103.Pq Tn IGMP , 104Transmission Control 105Protocol 106.Pq Tn TCP , 107and User Datagram Protocol 108.Pq Tn UDP . 109.Tn TCP 110is used to support the 111.Dv SOCK_STREAM 112abstraction while 113.Tn UDP 114is used to support the 115.Dv SOCK_DGRAM 116abstraction. A 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. For those 127programs which absolutely need to break addresses into their component 128parts, the following 129.Xr ioctl 2 130commands are provided for a datagram socket in the Internet domain; 131they have the same form as the 132.Dv SIOCSIFADDR 133and 134.Dv SIOCGIFADDR 135commands (see 136.Xr intro 4 ) . 137.Bl -tag -width ".Dv SIOCSIFNETMASK" 138.It Dv SIOCSIFNETMASK 139Set interface network mask. 140The network mask defines the network part of the address; 141if it contains more of the address than the address type would indicate, 142then subnets are in use. 143.It Dv SIOCGIFNETMASK 144Get interface network mask. 145.El 146.Sh ROUTING 147The current implementation of Internet protocols includes some routing-table 148adaptations to provide enhanced caching of certain end-to-end 149information necessary for Transaction TCP and Path MTU Discovery. The 150following changes are the most significant: 151.Bl -enum 152.It 153All IP routes, except those with the 154.Dv RTF_CLONING 155flag and those to multicast destinations, have the 156.Dv RTF_PRCLONING 157flag forcibly enabled (they are thus said to be 158.Dq "protocol cloning" ) . 159.It 160When the last reference to an IP route is dropped, the route is 161examined to determine if it was created by cloning such a route. If 162this is the case, the 163.Dv RTF_PROTO3 164flag is turned on, and the expiration timer is initialized to go off in 165.Va net.inet.ip.rtexpire 166seconds. 167If such a route is re-referenced, the flag and expiration timer are reset. 168.It 169A kernel timeout runs once every ten minutes, or sooner if there are 170soon-to-expire routes in the kernel routing table, and deletes the 171expired routes. 172.El 173.Pp 174A dynamic process is in place to modify the value of 175.Va net.inet.ip.rtexpire 176if the number of cached routes grows too large. 177If after an expiration run there are still more than 178.Va net.inet.ip.rtmaxcache 179unreferenced routes remaining, the rtexpire 180value is multiplied by \(34, and any routes which have longer 181expiration times have those times adjusted. This process is damped 182somewhat by specification of a minimum rtexpire value 183.Va ( net.inet.ip.rtminexpire ) , 184and by restricting the reduction to once in a ten-minute period. 185.Pp 186If some external process deletes the original route from which a 187protocol-cloned route was generated, the ``child route'' is deleted. 188(This is actually a generic mechanism in the routing code support for 189protocol-requested cloning.) 190.Pp 191No attempt is made to manage routes which were not created by protocol 192cloning; these are assumed to be static, under the management of an 193external routing process, or under the management of a link layer 194(e.g., 195.Tn ARP 196for Ethernets). 197.Pp 198Only certain types of network activity will result in the cloning of a 199route using this mechanism. Specifically, those protocols (such as 200.Tn TCP 201and 202.Tn UDP ) 203which themselves cache a long-lasting reference to route for a destination 204will trigger the mechanism; whereas raw 205.Tn IP 206packets, whether locally-generated or forwarded, will not. 207.Ss MIB Variables 208A number of variables are implemented in the net.inet branch of the 209.Xr sysctl 3 210MIB. 211In addition to the variables supported by the transport protocols 212(for which the respective manual pages may be consulted), 213the following general variables are defined: 214.Bl -tag -width IPCTL_FASTFORWARDING 215.It Dv IPCTL_FORWARDING 216.Pq ip.forwarding 217Boolean: enable/disable forwarding of IP packets. 218Defaults to off. 219.It Dv IPCTL_FASTFORWARDING 220.Pq ip.fastforwarding 221Boolean: enable/disable the use of fast IP forwarding code. 222Defaults to off. 223When fast forwarding is enabled, IP packets are forwarded directly to 224the appropriate network interface with a minimal validity checking, which 225greatly improves the throughput. On the other hand, they bypass the 226standard procedures, such as IP option processing and 227.Xr ipfirewall 4 228checking. 229It is not guaranteed that every packet will be fast-forwarded. 230.It Dv IPCTL_SENDREDIRECTS 231.Pq ip.redirect 232Boolean: enable/disable sending of ICMP redirects in response to 233unforwardable 234.Tn IP 235packets. 236Defaults to on. 237.It Dv IPCTL_DEFTTL 238.Pq ip.ttl 239Integer: default time-to-live 240.Pq Dq TTL 241to use for outgoing 242.Tn IP 243packets. 244.It Dv IPCTL_SOURCEROUTE 245.Pq ip.sourceroute 246Boolean: enable/disable forwarding of source-routed IP packets (default false). 247.It Dv IPCTL_RTEXPIRE 248.Pq ip.rtexpire 249Integer: lifetime in seconds of protocol-cloned 250.Tn IP 251routes after the last reference drops (default one hour). This value 252varies dynamically as described above. 253.It Dv IPCTL_RTMINEXPIRE 254.Pq ip.rtminexpire 255Integer: minimum value of ip.rtexpire (default ten seconds). This 256value has no effect on user modifications, but restricts the dynamic 257adaptation described above. 258.It Dv IPCTL_RTMAXCACHE 259.Pq ip.rtmaxcache 260Integer: trigger level of cached, unreferenced, protocol-cloned routes 261which initiates dynamic adaptation (default 128). 262.El 263.Sh SEE ALSO 264.Xr ioctl 2 , 265.Xr socket 2 , 266.Xr sysctl 3 , 267.Xr icmp 4 , 268.Xr intro 4 , 269.Xr ip 4 , 270.Xr ipfirewall 4 , 271.Xr tcp 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