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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.\" $DragonFly: src/share/man/man4/inet.4,v 1.8 2008/05/02 02:05:05 swildner Exp $ 35.\" 36.Dd February 14, 1995 37.Dt INET 4 38.Os 39.Sh NAME 40.Nm inet 41.Nd Internet protocol family 42.Sh SYNOPSIS 43.In sys/types.h 44.In netinet/in.h 45.Sh DESCRIPTION 46The Internet protocol family is a collection of protocols 47layered atop the 48.Em Internet Protocol 49.Pq Tn IP 50transport layer, and utilizing the Internet address format. 51The Internet family provides protocol support for the 52.Dv SOCK_STREAM , SOCK_DGRAM , 53and 54.Dv SOCK_RAW 55socket types; the 56.Dv SOCK_RAW 57interface provides access to the 58.Tn IP 59protocol. 60.Sh ADDRESSING 61Internet addresses are four byte quantities, stored in 62network standard format (on the 63.Tn VAX 64these are word and byte 65reversed). The include file 66.In netinet/in.h 67defines this address 68as a discriminated union. 69.Pp 70Sockets bound to the Internet protocol family utilize 71the following addressing structure, 72.Bd -literal -offset indent 73struct sockaddr_in { 74 u_char sin_len; 75 u_char sin_family; 76 u_short sin_port; 77 struct in_addr sin_addr; 78 char sin_zero[8]; 79}; 80.Ed 81.Pp 82Sockets may be created with the local address 83.Dv INADDR_ANY 84to affect 85.Dq wildcard 86matching on incoming messages. 87The address in a 88.Xr connect 2 89or 90.Xr sendto 2 91call may be given as 92.Dv INADDR_ANY 93to mean 94.Dq this host . 95The distinguished address 96.Dv INADDR_BROADCAST 97is allowed as a shorthand for the broadcast address on the primary 98network if the first network configured supports broadcast. 99.Sh PROTOCOLS 100The Internet protocol family is comprised of 101the 102.Tn IP 103network protocol, Internet Control 104Message Protocol 105.Pq Tn ICMP , 106Internet Group Management Protocol 107.Pq Tn IGMP , 108Transmission Control 109Protocol 110.Pq Tn TCP , 111and User Datagram Protocol 112.Pq Tn UDP . 113.Tn TCP 114is used to support the 115.Dv SOCK_STREAM 116abstraction while 117.Tn UDP 118is used to support the 119.Dv SOCK_DGRAM 120abstraction. A 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 32-bit Internet address contains both network and host parts. 130However, direct examination of addresses is discouraged. For those 131programs which absolutely need to break addresses into their component 132parts, the following 133.Xr ioctl 2 134commands are provided for a datagram socket in the Internet domain; 135they have the same form as the 136.Dv SIOCSIFADDR 137and 138.Dv SIOCGIFADDR 139commands (see 140.Xr intro 4 ) . 141.Bl -tag -width ".Dv SIOCSIFNETMASK" 142.It Dv SIOCSIFNETMASK 143Set interface network mask. 144The network mask defines the network part of the address; 145if it contains more of the address than the address type would indicate, 146then subnets are in use. 147.It Dv SIOCGIFNETMASK 148Get interface network mask. 149.El 150.Sh ROUTING 151The current implementation of Internet protocols includes some routing-table 152adaptations to provide enhanced caching of certain end-to-end 153information necessary for Transaction TCP and Path MTU Discovery. The 154following changes are the most significant: 155.Bl -enum 156.It 157All IP routes, except those with the 158.Dv RTF_CLONING 159flag and those to multicast destinations, have the 160.Dv RTF_PRCLONING 161flag forcibly enabled (they are thus said to be 162.Dq "protocol cloning" ) . 163.It 164When the last reference to an IP route is dropped, the route is 165examined to determine if it was created by cloning such a route. If 166this is the case, the 167.Dv RTF_PROTO3 168flag is turned on, and the expiration timer is initialized to go off in 169.Va net.inet.ip.rtexpire 170seconds. 171If such a route is re-referenced, the flag and expiration timer are reset. 172.It 173A kernel timeout runs once every ten minutes, or sooner if there are 174soon-to-expire routes in the kernel routing table, and deletes the 175expired routes. 176.El 177.Pp 178A dynamic process is in place to modify the value of 179.Va net.inet.ip.rtexpire 180if the number of cached routes grows too large. 181If after an expiration run there are still more than 182.Va net.inet.ip.rtmaxcache 183unreferenced routes remaining, the rtexpire 184value is multiplied by \(34, and any routes which have longer 185expiration times have those times adjusted. This process is damped 186somewhat by specification of a minimum rtexpire value 187.Va ( net.inet.ip.rtminexpire ) , 188and by restricting the reduction to once in a ten-minute period. 189.Pp 190If some external process deletes the original route from which a 191protocol-cloned route was generated, the ``child route'' is deleted. 192(This is actually a generic mechanism in the routing code support for 193protocol-requested cloning.) 194.Pp 195No attempt is made to manage routes which were not created by protocol 196cloning; these are assumed to be static, under the management of an 197external routing process, or under the management of a link layer 198(e.g., 199.Tn ARP 200for Ethernets). 201.Pp 202Only certain types of network activity will result in the cloning of a 203route using this mechanism. Specifically, those protocols (such as 204.Tn TCP 205and 206.Tn UDP ) 207which themselves cache a long-lasting reference to route for a destination 208will trigger the mechanism; whereas raw 209.Tn IP 210packets, whether locally-generated or forwarded, will not. 211.Ss MIB Variables 212A number of variables are implemented in the net.inet branch of the 213.Xr sysctl 3 214MIB. 215In addition to the variables supported by the transport protocols 216(for which the respective manual pages may be consulted), 217the following general variables are defined: 218.Bl -tag -width IPCTL_FASTFORWARDING 219.It Dv IPCTL_FORWARDING 220.Pq ip.forwarding 221Boolean: enable/disable forwarding of IP packets. 222Defaults to off. 223.It Dv IPCTL_FASTFORWARDING 224.Pq ip.fastforwarding 225Boolean: enable/disable the use of fast IP forwarding code. 226Defaults to off. 227When fast forwarding is enabled, IP packets are forwarded directly to 228the appropriate network interface with a minimal validity checking, which 229greatly improves the throughput. On the other hand, they bypass the 230standard procedures, such as IP option processing and 231.Xr ipfirewall 4 232checking. 233It is not guaranteed that every packet will be fast-forwarded. 234.It Dv IPCTL_SENDREDIRECTS 235.Pq ip.redirect 236Boolean: enable/disable sending of ICMP redirects in response to 237unforwardable 238.Tn IP 239packets. 240Defaults to on. 241.It Dv IPCTL_DEFTTL 242.Pq ip.ttl 243Integer: default time-to-live 244.Pq Dq TTL 245to use for outgoing 246.Tn IP 247packets. 248.It Dv IPCTL_SOURCEROUTE 249.Pq ip.sourceroute 250Boolean: enable/disable forwarding of source-routed IP packets (default false). 251.It Dv IPCTL_RTEXPIRE 252.Pq ip.rtexpire 253Integer: lifetime in seconds of protocol-cloned 254.Tn IP 255routes after the last reference drops (default one hour). This value 256varies dynamically as described above. 257.It Dv IPCTL_RTMINEXPIRE 258.Pq ip.rtminexpire 259Integer: minimum value of ip.rtexpire (default ten seconds). This 260value has no effect on user modifications, but restricts the dynamic 261adaptation described above. 262.It Dv IPCTL_RTMAXCACHE 263.Pq ip.rtmaxcache 264Integer: trigger level of cached, unreferenced, protocol-cloned routes 265which initiates dynamic adaptation (default 128). 266.El 267.Sh SEE ALSO 268.Xr ioctl 2 , 269.Xr socket 2 , 270.Xr sysctl 3 , 271.Xr icmp 4 , 272.Xr intro 4 , 273.Xr ip 4 , 274.Xr ipfirewall 4 , 275.Xr tcp 4 , 276.Xr ttcp 4 , 277.Xr udp 4 278.Rs 279.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 280.%B PS1 281.%N 7 282.Re 283.Rs 284.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 285.%B PS1 286.%N 8 287.Re 288.Sh CAVEAT 289The Internet protocol support is subject to change as 290the Internet protocols develop. Users should not depend 291on details of the current implementation, but rather 292the services exported. 293.Sh HISTORY 294The 295.Nm 296protocol interface appeared in 297.Bx 4.2 . 298The 299.Dq protocol cloning 300code appeared in 301.Fx 2.1 . 302