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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.Dd September 8, 2022 29.Dt INET 4 30.Os 31.Sh NAME 32.Nm inet 33.Nd Internet protocol family 34.Sh SYNOPSIS 35.In sys/types.h 36.In netinet/in.h 37.Sh DESCRIPTION 38The Internet protocol family is a collection of protocols 39layered atop the 40.Em Internet Protocol 41.Pq Tn IP 42transport layer, and utilizing the Internet address format. 43The Internet family provides protocol support for the 44.Dv SOCK_STREAM , SOCK_DGRAM , 45and 46.Dv SOCK_RAW 47socket types; the 48.Dv SOCK_RAW 49interface provides access to the 50.Tn IP 51protocol. 52.Sh ADDRESSING 53Internet addresses are four byte quantities, stored in 54network standard format (on little endian machines, such as the 55.Tn alpha , 56.Tn amd64 57and 58.Tn i386 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 uint8_t sin_len; 70 sa_family_t sin_family; 71 in_port_t 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 126.Nm 127address on an interface consist of the address itself, the 128netmask, either broadcast address in case of a broadcast 129interface or peers address in case of point-to-point interface. 130The following 131.Xr ioctl 2 132commands are provided for a datagram socket in the Internet domain: 133.Pp 134.Bl -tag -width ".Dv SIOCGIFBRDADDR" -offset indent -compact 135.It Dv SIOCAIFADDR 136Add address to an interface. 137The command requires 138.Ft struct in_aliasreq 139as argument. 140.It Dv SIOCDIFADDR 141Delete address from an interface. 142The command requires 143.Ft struct ifreq 144as argument. 145.It Dv SIOCGIFADDR 146.It Dv SIOCGIFBRDADDR 147.It Dv SIOCGIFDSTADDR 148.It Dv SIOCGIFNETMASK 149Return address information from interface. 150The returned value is in 151.Ft struct ifreq . 152This way of address information retrieval is obsoleted, a 153preferred way is to use 154.Xr getifaddrs 3 155API. 156.El 157.Ss MIB (sysctl) Variables 158In addition to the variables supported by the transport protocols in 159.Va net.inet 160(for which the respective manual pages may be consulted), 161there are a number of general variables implemented in the 162.Va net.inet.ip 163branch of the 164.Xr sysctl 3 165MIB, which can be also read or modified with 166.Xr sysctl 8 . 167The following general variables are defined: 168.Bl -tag -width ".Va accept_sourceroute" 169.It Va accept_sourceroute 170Boolean: enable/disable accepting of source-routed IP packets (default false). 171.It Va allow_net0 172Boolean: allow experimental use of addresses in 0.0.0.0/8 as endpoints, 173and allow forwarding of packets with these addresses. 174.It Va allow_net240 175Boolean: allow experimental use of addresses in 240.0.0.0/4 as endpoints, 176and allow forwarding of packets with these addresses. 177.It Va curfrags 178Integer: Current number of IPv4 fragments across all reassembly queues 179in all VNETs (read-only). 180.It Va forwarding 181Boolean: enable/disable forwarding of IP packets. 182Defaults to off. 183.It Va fragpackets 184Integer: Current number of IPv4 fragment reassembly queue entries 185for the VNET (read-only). 186.It Va fragttl 187Integer: time to live for IPv4 packet fragments in the per-VNET reassemby queue. 188.It Va loopback_prefixlen 189Integer: prefix length of the address space reserved for loopback purposes. 190The default is 8, meaning that 127.0.0.0/8 is reserved for loopback, 191and cannot be sent, received, or forwarded on a non-loopback interface. 192Use of other values is experimental. 193.It Va maxfragbucketsize 194Integer: maximum number of reassembly queues per bucket. 195Fragmented packets are hashed to buckets. 196Each bucket has a list of reassembly queues. 197The system must compare the incoming packets to the existing reassembly queues 198in the bucket to find a matching reassembly queue. 199To preserve system resources, the system limits the number of reassembly 200queues allowed in each bucket. 201This limit is recalculated when the number of mbuf clusters is changed or 202when the value of 203.Va maxfragpackets 204changes. 205This is a per-VNET limit. 206.It Va maxfragpackets 207Integer: maximum number of fragmented packets the host will accept and 208simultaneously hold in the reassembly queue for a particular VNET. 2090 means that the host will not accept any fragmented packets for that VNET. 210\-1 means that the host will not apply this limit for that VNET. 211This limit is recalculated when the number of mbuf clusters is changed. 212This is a per-VNET limit. 213.It Va maxfrags 214Integer: maximum number of fragments the host will accept and simultaneously 215hold across all reassembly queues in all VNETs. 216If set to 0, reassembly is disabled. 217If set to -1, this limit is not applied. 218This limit is recalculated when the number of mbuf clusters is changed. 219This is a global limit. 220.It Va maxfragsperpacket 221Integer: maximum number of fragments the host will accept and hold 222in the reassembly queue for a packet. 2230 means that the host will not accept any fragmented packets for the VNET. 224This is a per-VNET limit. 225.It Va mcast 226Variables under the 227.Va net.inet.ip.mcast 228node are documented in 229.Xr ip 4 . 230.It Va no_same_prefix 231Boolean: Refuse to create same prefixes on different interfaces. 232This is a per-VNET value. 233.It Va portrange 234Variables under the 235.Va net.inet.ip.portrange 236node control port ranges used by transport protocols; see 237.Xr ip 4 238for details. 239.It Va process_options 240Integer: control IP options processing. 241By setting this variable to 0, all IP options in the incoming packets 242will be ignored, and the packets will be passed unmodified. 243By setting to 1, IP options in the incoming packets will be processed 244accordingly. 245By setting to 2, an 246.Tn ICMP 247.Dq "prohibited by filter" 248message will be sent back in response to incoming packets with IP options. 249Default is 1. 250This 251.Xr sysctl 8 252variable affects packets destined for a local host as well as packets 253forwarded to some other host. 254.It Va random_id 255Boolean: control IP IDs generation behavior. 256Setting this 257.Xr sysctl 8 258to 1 causes the ID field in 259.Em non-atomic 260IP datagrams (or all IP datagrams, if 261.Va rfc6864 262is disabled) to be randomized instead of incremented by 1 with each packet 263generated. 264This closes a minor information leak which allows remote observers to 265determine the rate of packet generation on the machine by watching the 266counter. 267At the same time, on high-speed links, it can decrease the ID reuse 268cycle greatly. 269Default is 0 (sequential IP IDs). 270IPv6 flow IDs and fragment IDs are always random. 271.It Va random_id_collisions 272Integer: count of IP ID collisions (read-only, per-VNET). 273.It Va random_id_period 274Integer: size of the IP ID array, which is the number of previous packets 275for which the IDs are recorded. 276The number must be between 512 and 32768 inclusive. 277This is a per-VNET value. 278.It Va random_id_total 279Integer: count of IP IDs created (read-only, per-VNET). 280.It Va reass_hashsize 281Number of hash slots in the IPv4 reassembly queue (loader tunable). 282.It Va redirect 283Boolean: enable/disable sending of ICMP redirects in response to 284.Tn IP 285packets for which a better, and for the sender directly reachable, route 286and next hop is known. 287Defaults to on. 288.It Va rfc1122_strong_es 289Boolean: in non-forwarding mode 290.Pq forwarding is disabled 291partially implement the Strong End System model per RFC1122. 292If a packet with destination address that is local arrives on a different 293interface than the interface the address belongs to, the packet would be 294silently dropped. 295Enabling this option may break certain setups, e.g. having an alias address(es) 296on loopback that are expected to be reachable by outside traffic. 297Enabling some other network features, e.g. 298.Xr carp 4 299or destination address rewriting 300.Xr pfil 4 301filters may override and bypass this check. 302Disabled by default. 303.It Va rfc6864 304Boolean: control IP IDs generation behaviour. 305True value enables RFC6864 support, which specifies that IP ID field of 306.Em atomic 307datagrams can be set to any value. 308The 309.Fx implementation sets it to zero. 310Enabled by default. 311.It Va source_address_validation 312Boolean: perform source address validation for packets destined for the local 313host. 314Consider this as following Section 3.2 of RFC3704/BCP84, where we treat local 315host as our own infrastructure. 316Forwarded packets are unaffected by this 317and it should not be considered an anti-spoof feature for a router. 318Enabled by default. 319.It Va sourceroute 320Boolean: enable/disable forwarding of source-routed IP packets (default false). 321.It Va ttl 322Integer: default time-to-live 323.Pq Dq TTL 324to use for outgoing 325.Tn IP 326packets. 327.El 328.Sh SEE ALSO 329.Xr ioctl 2 , 330.Xr socket 2 , 331.Xr getifaddrs 3 , 332.Xr sysctl 3 , 333.Xr icmp 4 , 334.Xr intro 4 , 335.Xr ip 4 , 336.Xr ipfirewall 4 , 337.Xr route 4 , 338.Xr tcp 4 , 339.Xr udp 4 , 340.Xr sysctl 8 , 341.Xr pfil 9 342.Rs 343.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 344.%B PS1 345.%N 7 346.Re 347.Rs 348.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 349.%B PS1 350.%N 8 351.Re 352.Sh HISTORY 353The 354.Nm 355protocol interface appeared in 356.Bx 4.2 . 357The 358.Dq protocol cloning 359code appeared in 360.Fx 2.1 . 361.Sh CAVEATS 362The Internet protocol support is subject to change as 363the Internet protocols develop. 364Users should not depend 365on details of the current implementation, but rather 366the services exported. 367