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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 July 20, 2022 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. 153The returned value is 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 161In addition to the variables supported by the transport protocols in 162.Va net.inet 163(for which the respective manual pages may be consulted), 164there are a number of general variables implemented in the 165.Va net.inet.ip 166branch of the 167.Xr sysctl 3 168MIB. 169The following general variables are defined: 170.Bl -tag -width ".Va accept_sourceroute" 171.It Va accept_sourceroute 172Boolean: enable/disable accepting of source-routed IP packets (default false). 173.It Va allow_net0 174Boolean: allow experimental use of addresses in 0.0.0.0/8 as endpoints, 175and allow forwarding of packets with these addresses. 176.It Va allow_net240 177Boolean: allow experimental use of addresses in 240.0.0.0/4 as endpoints, 178and allow forwarding of packets with these addresses. 179.It Va forwarding 180Boolean: enable/disable forwarding of IP packets. 181Defaults to off. 182.It Va loopback_prefixlen 183Integer: prefix length of the address space reserved for loopback purposes. 184The default is 8, meaning that 127.0.0.0/8 is reserved for loopback, 185and cannot be sent, received, or forwarded on a non-loopback interface. 186Use of other values is experimental. 187.It Va maxfragbucketsize 188Integer: maximum number of reassembly queues per bucket. 189Fragmented packets are hashed to buckets. 190Each bucket has a list of reassembly queues. 191The system must compare the incoming packets to the existing reassembly queues 192in the bucket to find a matching reassembly queue. 193To preserve system resources, the system limits the number of reassembly 194queues allowed in each bucket. 195This limit is recalculated when the number of mbuf clusters is changed or 196when the value of 197.Va maxfragpackets 198changes. 199This is a per-VNET limit. 200.It Va maxfragpackets 201Integer: maximum number of fragmented packets the host will accept and 202simultaneously hold in the reassembly queue for a particular VNET. 2030 means that the host will not accept any fragmented packets for that VNET. 204\-1 means that the host will not apply this limit for that VNET. 205This limit is recalculated when the number of mbuf clusters is changed. 206This is a per-VNET limit. 207.It Va maxfrags 208Integer: maximum number of fragments the host will accept and simultaneously 209hold across all reassembly queues in all VNETs. 210If set to 0, reassembly is disabled. 211If set to -1, this limit is not applied. 212This limit is recalculated when the number of mbuf clusters is changed. 213This is a global limit. 214.It Va maxfragsperpacket 215Integer: maximum number of fragments the host will accept and hold 216in the reassembly queue for a packet. 2170 means that the host will not accept any fragmented packets for the VNET. 218This is a per-VNET limit. 219.It Va process_options 220Integer: control IP options processing. 221By setting this variable to 0, all IP options in the incoming packets 222will be ignored, and the packets will be passed unmodified. 223By setting to 1, IP options in the incoming packets will be processed 224accordingly. 225By setting to 2, an 226.Tn ICMP 227.Dq "prohibited by filter" 228message will be sent back in response to incoming packets with IP options. 229Default is 1. 230This 231.Xr sysctl 8 232variable affects packets destined for a local host as well as packets 233forwarded to some other host. 234.It Va random_id 235Boolean: control IP IDs generation behavior. 236Setting this 237.Xr sysctl 8 238to 1 causes the ID field in 239.Em non-atomic 240IP datagrams (or all IP datagrams, if 241.Va rfc6864 242is disabled) to be randomized instead of incremented by 1 with each packet 243generated. 244This closes a minor information leak which allows remote observers to 245determine the rate of packet generation on the machine by watching the 246counter. 247At the same time, on high-speed links, it can decrease the ID reuse 248cycle greatly. 249Default is 0 (sequential IP IDs). 250IPv6 flow IDs and fragment IDs are always random. 251.It Va redirect 252Boolean: enable/disable sending of ICMP redirects in response to 253.Tn IP 254packets for which a better, and for the sender directly reachable, route 255and next hop is known. 256Defaults to on. 257.It Va rfc1122_strong_es 258Boolean: in non-forwarding mode 259.Pq forwarding is disabled 260partially implement the Strong End System model per RFC1122. 261If a packet with destination address that is local arrives on a different 262interface than the interface the address belongs to, the packet would be 263silently dropped. 264Enabling this option may break certain setups, e.g. having an alias address(es) 265on loopback that are expected to be reachable by outside traffic. 266Enabling some other network features, e.g. 267.Xr carp 4 268or destination address rewriting 269.Xr pfil 4 270filters may override and bypass this check. 271Disabled by default. 272.It Va rfc6864 273Boolean: control IP IDs generation behaviour. 274True value enables RFC6864 support, which specifies that IP ID field of 275.Em atomic 276datagrams can be set to any value. 277The 278.Fx implementation sets it to zero. 279Enabled by default. 280.It Va source_address_validation 281Boolean: perform source address validation for packets destined for the local 282host. 283Consider this as following Section 3.2 of RFC3704/BCP84, where we treat local 284host as our own infrastructure. 285Forwarded packets are unaffected by this 286and it should not be considered an anti-spoof feature for a router. 287Enabled by default. 288.It Va sourceroute 289Boolean: enable/disable forwarding of source-routed IP packets (default false). 290.It Va ttl 291Integer: default time-to-live 292.Pq Dq TTL 293to use for outgoing 294.Tn IP 295packets. 296.El 297.Sh SEE ALSO 298.Xr ioctl 2 , 299.Xr socket 2 , 300.Xr getifaddrs 3 , 301.Xr sysctl 3 , 302.Xr icmp 4 , 303.Xr intro 4 , 304.Xr ip 4 , 305.Xr ipfirewall 4 , 306.Xr route 4 , 307.Xr tcp 4 , 308.Xr udp 4 , 309.Xr pfil 9 310.Rs 311.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 312.%B PS1 313.%N 7 314.Re 315.Rs 316.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 317.%B PS1 318.%N 8 319.Re 320.Sh HISTORY 321The 322.Nm 323protocol interface appeared in 324.Bx 4.2 . 325The 326.Dq protocol cloning 327code appeared in 328.Fx 2.1 . 329.Sh CAVEATS 330The Internet protocol support is subject to change as 331the Internet protocols develop. 332Users should not depend 333on details of the current implementation, but rather 334the services exported. 335