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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 September 8, 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 (sysctl) 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, which can be also read or modified with 169.Xr sysctl 8 . 170The following general variables are defined: 171.Bl -tag -width ".Va accept_sourceroute" 172.It Va accept_sourceroute 173Boolean: enable/disable accepting of source-routed IP packets (default false). 174.It Va allow_net0 175Boolean: allow experimental use of addresses in 0.0.0.0/8 as endpoints, 176and allow forwarding of packets with these addresses. 177.It Va allow_net240 178Boolean: allow experimental use of addresses in 240.0.0.0/4 as endpoints, 179and allow forwarding of packets with these addresses. 180.It Va curfrags 181Integer: Current number of IPv4 fragments across all reassembly queues 182in all VNETs (read-only). 183.It Va forwarding 184Boolean: enable/disable forwarding of IP packets. 185Defaults to off. 186.It Va fragpackets 187Integer: Current number of IPv4 fragment reassembly queue entries 188for the VNET (read-only). 189.It Va fragttl 190Integer: time to live for IPv4 packet fragments in the per-VNET reassemby queue. 191.It Va loopback_prefixlen 192Integer: prefix length of the address space reserved for loopback purposes. 193The default is 8, meaning that 127.0.0.0/8 is reserved for loopback, 194and cannot be sent, received, or forwarded on a non-loopback interface. 195Use of other values is experimental. 196.It Va maxfragbucketsize 197Integer: maximum number of reassembly queues per bucket. 198Fragmented packets are hashed to buckets. 199Each bucket has a list of reassembly queues. 200The system must compare the incoming packets to the existing reassembly queues 201in the bucket to find a matching reassembly queue. 202To preserve system resources, the system limits the number of reassembly 203queues allowed in each bucket. 204This limit is recalculated when the number of mbuf clusters is changed or 205when the value of 206.Va maxfragpackets 207changes. 208This is a per-VNET limit. 209.It Va maxfragpackets 210Integer: maximum number of fragmented packets the host will accept and 211simultaneously hold in the reassembly queue for a particular VNET. 2120 means that the host will not accept any fragmented packets for that VNET. 213\-1 means that the host will not apply this limit for that VNET. 214This limit is recalculated when the number of mbuf clusters is changed. 215This is a per-VNET limit. 216.It Va maxfrags 217Integer: maximum number of fragments the host will accept and simultaneously 218hold across all reassembly queues in all VNETs. 219If set to 0, reassembly is disabled. 220If set to -1, this limit is not applied. 221This limit is recalculated when the number of mbuf clusters is changed. 222This is a global limit. 223.It Va maxfragsperpacket 224Integer: maximum number of fragments the host will accept and hold 225in the reassembly queue for a packet. 2260 means that the host will not accept any fragmented packets for the VNET. 227This is a per-VNET limit. 228.It Va mcast 229Variables under the 230.Va net.inet.ip.mcast 231node are documented in 232.Xr ip 4 . 233.It Va no_same_prefix 234Boolean: Refuse to create same prefixes on different interfaces. 235This is a per-VNET value. 236.It Va portrange 237Variables under the 238.Va net.inet.ip.portrange 239node control port ranges used by transport protocols; see 240.Xr ip 4 241for details. 242.It Va process_options 243Integer: control IP options processing. 244By setting this variable to 0, all IP options in the incoming packets 245will be ignored, and the packets will be passed unmodified. 246By setting to 1, IP options in the incoming packets will be processed 247accordingly. 248By setting to 2, an 249.Tn ICMP 250.Dq "prohibited by filter" 251message will be sent back in response to incoming packets with IP options. 252Default is 1. 253This 254.Xr sysctl 8 255variable affects packets destined for a local host as well as packets 256forwarded to some other host. 257.It Va random_id 258Boolean: control IP IDs generation behavior. 259Setting this 260.Xr sysctl 8 261to 1 causes the ID field in 262.Em non-atomic 263IP datagrams (or all IP datagrams, if 264.Va rfc6864 265is disabled) to be randomized instead of incremented by 1 with each packet 266generated. 267This closes a minor information leak which allows remote observers to 268determine the rate of packet generation on the machine by watching the 269counter. 270At the same time, on high-speed links, it can decrease the ID reuse 271cycle greatly. 272Default is 0 (sequential IP IDs). 273IPv6 flow IDs and fragment IDs are always random. 274.It Va random_id_collisions 275Integer: count of IP ID collisions (read-only, per-VNET). 276.It Va random_id_period 277Integer: size of the IP ID array, which is the number of previous packets 278for which the IDs are recorded. 279The number must be between 512 and 32768 inclusive. 280This is a per-VNET value. 281.It Va random_id_total 282Integer: count of IP IDs created (read-only, per-VNET). 283.It Va reass_hashsize 284Number of hash slots in the IPv4 reassembly queue (loader tunable). 285.It Va redirect 286Boolean: enable/disable sending of ICMP redirects in response to 287.Tn IP 288packets for which a better, and for the sender directly reachable, route 289and next hop is known. 290Defaults to on. 291.It Va rfc1122_strong_es 292Boolean: in non-forwarding mode 293.Pq forwarding is disabled 294partially implement the Strong End System model per RFC1122. 295If a packet with destination address that is local arrives on a different 296interface than the interface the address belongs to, the packet would be 297silently dropped. 298Enabling this option may break certain setups, e.g. having an alias address(es) 299on loopback that are expected to be reachable by outside traffic. 300Enabling some other network features, e.g. 301.Xr carp 4 302or destination address rewriting 303.Xr pfil 4 304filters may override and bypass this check. 305Disabled by default. 306.It Va rfc6864 307Boolean: control IP IDs generation behaviour. 308True value enables RFC6864 support, which specifies that IP ID field of 309.Em atomic 310datagrams can be set to any value. 311The 312.Fx implementation sets it to zero. 313Enabled by default. 314.It Va source_address_validation 315Boolean: perform source address validation for packets destined for the local 316host. 317Consider this as following Section 3.2 of RFC3704/BCP84, where we treat local 318host as our own infrastructure. 319Forwarded packets are unaffected by this 320and it should not be considered an anti-spoof feature for a router. 321Enabled by default. 322.It Va sourceroute 323Boolean: enable/disable forwarding of source-routed IP packets (default false). 324.It Va ttl 325Integer: default time-to-live 326.Pq Dq TTL 327to use for outgoing 328.Tn IP 329packets. 330.El 331.Sh SEE ALSO 332.Xr ioctl 2 , 333.Xr socket 2 , 334.Xr getifaddrs 3 , 335.Xr sysctl 3 , 336.Xr icmp 4 , 337.Xr intro 4 , 338.Xr ip 4 , 339.Xr ipfirewall 4 , 340.Xr route 4 , 341.Xr tcp 4 , 342.Xr udp 4 , 343.Xr sysctl 8 , 344.Xr pfil 9 345.Rs 346.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 347.%B PS1 348.%N 7 349.Re 350.Rs 351.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 352.%B PS1 353.%N 8 354.Re 355.Sh HISTORY 356The 357.Nm 358protocol interface appeared in 359.Bx 4.2 . 360The 361.Dq protocol cloning 362code appeared in 363.Fx 2.1 . 364.Sh CAVEATS 365The Internet protocol support is subject to change as 366the Internet protocols develop. 367Users should not depend 368on details of the current implementation, but rather 369the services exported. 370