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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.\" 30.Dd September 8, 2022 31.Dt INET 4 32.Os 33.Sh NAME 34.Nm inet 35.Nd Internet protocol family 36.Sh SYNOPSIS 37.In sys/types.h 38.In netinet/in.h 39.Sh DESCRIPTION 40The Internet protocol family is a collection of protocols 41layered atop the 42.Em Internet Protocol 43.Pq Tn IP 44transport layer, and utilizing the Internet address format. 45The Internet family provides protocol support for the 46.Dv SOCK_STREAM , SOCK_DGRAM , 47and 48.Dv SOCK_RAW 49socket types; the 50.Dv SOCK_RAW 51interface provides access to the 52.Tn IP 53protocol. 54.Sh ADDRESSING 55Internet addresses are four byte quantities, stored in 56network standard format (on little endian machines, such as the 57.Tn alpha , 58.Tn amd64 59and 60.Tn i386 61these are word and byte reversed). 62The include file 63.In netinet/in.h 64defines this address 65as a discriminated union. 66.Pp 67Sockets bound to the Internet protocol family utilize 68the following addressing structure, 69.Bd -literal -offset indent 70struct sockaddr_in { 71 uint8_t sin_len; 72 sa_family_t sin_family; 73 in_port_t sin_port; 74 struct in_addr sin_addr; 75 char sin_zero[8]; 76}; 77.Ed 78.Pp 79Sockets may be created with the local address 80.Dv INADDR_ANY 81to affect 82.Dq wildcard 83matching on incoming messages. 84The address in a 85.Xr connect 2 86or 87.Xr sendto 2 88call may be given as 89.Dv INADDR_ANY 90to mean 91.Dq this host . 92The distinguished address 93.Dv INADDR_BROADCAST 94is allowed as a shorthand for the broadcast address on the primary 95network if the first network configured supports broadcast. 96.Sh PROTOCOLS 97The Internet protocol family is comprised of 98the 99.Tn IP 100network protocol, Internet Control 101Message Protocol 102.Pq Tn ICMP , 103Internet Group Management Protocol 104.Pq Tn IGMP , 105Transmission Control 106Protocol 107.Pq Tn TCP , 108and User Datagram Protocol 109.Pq Tn UDP . 110.Tn TCP 111is used to support the 112.Dv SOCK_STREAM 113abstraction while 114.Tn UDP 115is used to support the 116.Dv SOCK_DGRAM 117abstraction. 118A raw interface to 119.Tn IP 120is available 121by creating an Internet socket of type 122.Dv SOCK_RAW . 123The 124.Tn ICMP 125message protocol is accessible from a raw socket. 126.Pp 127The 128.Nm 129address on an interface consist of the address itself, the 130netmask, either broadcast address in case of a broadcast 131interface or peers address in case of point-to-point interface. 132The following 133.Xr ioctl 2 134commands are provided for a datagram socket in the Internet domain: 135.Pp 136.Bl -tag -width ".Dv SIOCGIFBRDADDR" -offset indent -compact 137.It Dv SIOCAIFADDR 138Add address to an interface. 139The command requires 140.Ft struct in_aliasreq 141as argument. 142.It Dv SIOCDIFADDR 143Delete address from an interface. 144The command requires 145.Ft struct ifreq 146as argument. 147.It Dv SIOCGIFADDR 148.It Dv SIOCGIFBRDADDR 149.It Dv SIOCGIFDSTADDR 150.It Dv SIOCGIFNETMASK 151Return address information from interface. 152The returned value is in 153.Ft struct ifreq . 154This way of address information retrieval is obsoleted, a 155preferred way is to use 156.Xr getifaddrs 3 157API. 158.El 159.Ss MIB (sysctl) Variables 160In addition to the variables supported by the transport protocols in 161.Va net.inet 162(for which the respective manual pages may be consulted), 163there are a number of general variables implemented in the 164.Va net.inet.ip 165branch of the 166.Xr sysctl 3 167MIB, which can be also read or modified with 168.Xr sysctl 8 . 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 curfrags 180Integer: Current number of IPv4 fragments across all reassembly queues 181in all VNETs (read-only). 182.It Va forwarding 183Boolean: enable/disable forwarding of IP packets. 184Defaults to off. 185.It Va fragpackets 186Integer: Current number of IPv4 fragment reassembly queue entries 187for the VNET (read-only). 188.It Va fragttl 189Integer: time to live for IPv4 packet fragments in the per-VNET reassemby queue. 190.It Va loopback_prefixlen 191Integer: prefix length of the address space reserved for loopback purposes. 192The default is 8, meaning that 127.0.0.0/8 is reserved for loopback, 193and cannot be sent, received, or forwarded on a non-loopback interface. 194Use of other values is experimental. 195.It Va maxfragbucketsize 196Integer: maximum number of reassembly queues per bucket. 197Fragmented packets are hashed to buckets. 198Each bucket has a list of reassembly queues. 199The system must compare the incoming packets to the existing reassembly queues 200in the bucket to find a matching reassembly queue. 201To preserve system resources, the system limits the number of reassembly 202queues allowed in each bucket. 203This limit is recalculated when the number of mbuf clusters is changed or 204when the value of 205.Va maxfragpackets 206changes. 207This is a per-VNET limit. 208.It Va maxfragpackets 209Integer: maximum number of fragmented packets the host will accept and 210simultaneously hold in the reassembly queue for a particular VNET. 2110 means that the host will not accept any fragmented packets for that VNET. 212\-1 means that the host will not apply this limit for that VNET. 213This limit is recalculated when the number of mbuf clusters is changed. 214This is a per-VNET limit. 215.It Va maxfrags 216Integer: maximum number of fragments the host will accept and simultaneously 217hold across all reassembly queues in all VNETs. 218If set to 0, reassembly is disabled. 219If set to -1, this limit is not applied. 220This limit is recalculated when the number of mbuf clusters is changed. 221This is a global limit. 222.It Va maxfragsperpacket 223Integer: maximum number of fragments the host will accept and hold 224in the reassembly queue for a packet. 2250 means that the host will not accept any fragmented packets for the VNET. 226This is a per-VNET limit. 227.It Va mcast 228Variables under the 229.Va net.inet.ip.mcast 230node are documented in 231.Xr ip 4 . 232.It Va no_same_prefix 233Boolean: Refuse to create same prefixes on different interfaces. 234This is a per-VNET value. 235.It Va portrange 236Variables under the 237.Va net.inet.ip.portrange 238node control port ranges used by transport protocols; see 239.Xr ip 4 240for details. 241.It Va process_options 242Integer: control IP options processing. 243By setting this variable to 0, all IP options in the incoming packets 244will be ignored, and the packets will be passed unmodified. 245By setting to 1, IP options in the incoming packets will be processed 246accordingly. 247By setting to 2, an 248.Tn ICMP 249.Dq "prohibited by filter" 250message will be sent back in response to incoming packets with IP options. 251Default is 1. 252This 253.Xr sysctl 8 254variable affects packets destined for a local host as well as packets 255forwarded to some other host. 256.It Va random_id 257Boolean: control IP IDs generation behavior. 258Setting this 259.Xr sysctl 8 260to 1 causes the ID field in 261.Em non-atomic 262IP datagrams (or all IP datagrams, if 263.Va rfc6864 264is disabled) to be randomized instead of incremented by 1 with each packet 265generated. 266This closes a minor information leak which allows remote observers to 267determine the rate of packet generation on the machine by watching the 268counter. 269At the same time, on high-speed links, it can decrease the ID reuse 270cycle greatly. 271Default is 0 (sequential IP IDs). 272IPv6 flow IDs and fragment IDs are always random. 273.It Va random_id_collisions 274Integer: count of IP ID collisions (read-only, per-VNET). 275.It Va random_id_period 276Integer: size of the IP ID array, which is the number of previous packets 277for which the IDs are recorded. 278The number must be between 512 and 32768 inclusive. 279This is a per-VNET value. 280.It Va random_id_total 281Integer: count of IP IDs created (read-only, per-VNET). 282.It Va reass_hashsize 283Number of hash slots in the IPv4 reassembly queue (loader tunable). 284.It Va redirect 285Boolean: enable/disable sending of ICMP redirects in response to 286.Tn IP 287packets for which a better, and for the sender directly reachable, route 288and next hop is known. 289Defaults to on. 290.It Va rfc1122_strong_es 291Boolean: in non-forwarding mode 292.Pq forwarding is disabled 293partially implement the Strong End System model per RFC1122. 294If a packet with destination address that is local arrives on a different 295interface than the interface the address belongs to, the packet would be 296silently dropped. 297Enabling this option may break certain setups, e.g. having an alias address(es) 298on loopback that are expected to be reachable by outside traffic. 299Enabling some other network features, e.g. 300.Xr carp 4 301or destination address rewriting 302.Xr pfil 4 303filters may override and bypass this check. 304Disabled by default. 305.It Va rfc6864 306Boolean: control IP IDs generation behaviour. 307True value enables RFC6864 support, which specifies that IP ID field of 308.Em atomic 309datagrams can be set to any value. 310The 311.Fx implementation sets it to zero. 312Enabled by default. 313.It Va source_address_validation 314Boolean: perform source address validation for packets destined for the local 315host. 316Consider this as following Section 3.2 of RFC3704/BCP84, where we treat local 317host as our own infrastructure. 318Forwarded packets are unaffected by this 319and it should not be considered an anti-spoof feature for a router. 320Enabled by default. 321.It Va sourceroute 322Boolean: enable/disable forwarding of source-routed IP packets (default false). 323.It Va ttl 324Integer: default time-to-live 325.Pq Dq TTL 326to use for outgoing 327.Tn IP 328packets. 329.El 330.Sh SEE ALSO 331.Xr ioctl 2 , 332.Xr socket 2 , 333.Xr getifaddrs 3 , 334.Xr sysctl 3 , 335.Xr icmp 4 , 336.Xr intro 4 , 337.Xr ip 4 , 338.Xr ipfirewall 4 , 339.Xr route 4 , 340.Xr tcp 4 , 341.Xr udp 4 , 342.Xr sysctl 8 , 343.Xr pfil 9 344.Rs 345.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 346.%B PS1 347.%N 7 348.Re 349.Rs 350.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 351.%B PS1 352.%N 8 353.Re 354.Sh HISTORY 355The 356.Nm 357protocol interface appeared in 358.Bx 4.2 . 359The 360.Dq protocol cloning 361code appeared in 362.Fx 2.1 . 363.Sh CAVEATS 364The Internet protocol support is subject to change as 365the Internet protocols develop. 366Users should not depend 367on details of the current implementation, but rather 368the services exported. 369