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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 August 1, 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 loopback_prefixlen 190Integer: prefix length of the address space reserved for loopback purposes. 191The default is 8, meaning that 127.0.0.0/8 is reserved for loopback, 192and cannot be sent, received, or forwarded on a non-loopback interface. 193Use of other values is experimental. 194.It Va maxfragbucketsize 195Integer: maximum number of reassembly queues per bucket. 196Fragmented packets are hashed to buckets. 197Each bucket has a list of reassembly queues. 198The system must compare the incoming packets to the existing reassembly queues 199in the bucket to find a matching reassembly queue. 200To preserve system resources, the system limits the number of reassembly 201queues allowed in each bucket. 202This limit is recalculated when the number of mbuf clusters is changed or 203when the value of 204.Va maxfragpackets 205changes. 206This is a per-VNET limit. 207.It Va maxfragpackets 208Integer: maximum number of fragmented packets the host will accept and 209simultaneously hold in the reassembly queue for a particular VNET. 2100 means that the host will not accept any fragmented packets for that VNET. 211\-1 means that the host will not apply this limit for that VNET. 212This limit is recalculated when the number of mbuf clusters is changed. 213This is a per-VNET limit. 214.It Va maxfrags 215Integer: maximum number of fragments the host will accept and simultaneously 216hold across all reassembly queues in all VNETs. 217If set to 0, reassembly is disabled. 218If set to -1, this limit is not applied. 219This limit is recalculated when the number of mbuf clusters is changed. 220This is a global limit. 221.It Va maxfragsperpacket 222Integer: maximum number of fragments the host will accept and hold 223in the reassembly queue for a packet. 2240 means that the host will not accept any fragmented packets for the VNET. 225This is a per-VNET limit. 226.It Va mcast 227Variables under the 228.Va net.inet.ip.mcast 229node are documented in 230.Xr ip 4 . 231.It Va no_same_prefix 232Boolean: Refuse to create same prefixes on different interfaces. 233This is a per-VNET value. 234.It Va portrange 235Variables under the 236.Va net.inet.ip.portrange 237node control port ranges used by transport protocols; see 238.Xr ip 4 239for details. 240.It Va process_options 241Integer: control IP options processing. 242By setting this variable to 0, all IP options in the incoming packets 243will be ignored, and the packets will be passed unmodified. 244By setting to 1, IP options in the incoming packets will be processed 245accordingly. 246By setting to 2, an 247.Tn ICMP 248.Dq "prohibited by filter" 249message will be sent back in response to incoming packets with IP options. 250Default is 1. 251This 252.Xr sysctl 8 253variable affects packets destined for a local host as well as packets 254forwarded to some other host. 255.It Va random_id 256Boolean: control IP IDs generation behavior. 257Setting this 258.Xr sysctl 8 259to 1 causes the ID field in 260.Em non-atomic 261IP datagrams (or all IP datagrams, if 262.Va rfc6864 263is disabled) to be randomized instead of incremented by 1 with each packet 264generated. 265This closes a minor information leak which allows remote observers to 266determine the rate of packet generation on the machine by watching the 267counter. 268At the same time, on high-speed links, it can decrease the ID reuse 269cycle greatly. 270Default is 0 (sequential IP IDs). 271IPv6 flow IDs and fragment IDs are always random. 272.It Va random_id_collisions 273Integer: count of IP ID collisions (read-only, per-VNET). 274.It Va random_id_period 275Integer: size of the IP ID array, which is the number of previous packets 276for which the IDs are recorded. 277The number must be between 512 and 32768 inclusive. 278This is a per-VNET value. 279.It Va random_id_total 280Integer: count of IP IDs created (read-only, per-VNET). 281.It Va redirect 282Boolean: enable/disable sending of ICMP redirects in response to 283.Tn IP 284packets for which a better, and for the sender directly reachable, route 285and next hop is known. 286Defaults to on. 287.It Va rfc1122_strong_es 288Boolean: in non-forwarding mode 289.Pq forwarding is disabled 290partially implement the Strong End System model per RFC1122. 291If a packet with destination address that is local arrives on a different 292interface than the interface the address belongs to, the packet would be 293silently dropped. 294Enabling this option may break certain setups, e.g. having an alias address(es) 295on loopback that are expected to be reachable by outside traffic. 296Enabling some other network features, e.g. 297.Xr carp 4 298or destination address rewriting 299.Xr pfil 4 300filters may override and bypass this check. 301Disabled by default. 302.It Va rfc6864 303Boolean: control IP IDs generation behaviour. 304True value enables RFC6864 support, which specifies that IP ID field of 305.Em atomic 306datagrams can be set to any value. 307The 308.Fx implementation sets it to zero. 309Enabled by default. 310.It Va source_address_validation 311Boolean: perform source address validation for packets destined for the local 312host. 313Consider this as following Section 3.2 of RFC3704/BCP84, where we treat local 314host as our own infrastructure. 315Forwarded packets are unaffected by this 316and it should not be considered an anti-spoof feature for a router. 317Enabled by default. 318.It Va sourceroute 319Boolean: enable/disable forwarding of source-routed IP packets (default false). 320.It Va ttl 321Integer: default time-to-live 322.Pq Dq TTL 323to use for outgoing 324.Tn IP 325packets. 326.El 327.Sh SEE ALSO 328.Xr ioctl 2 , 329.Xr socket 2 , 330.Xr getifaddrs 3 , 331.Xr sysctl 3 , 332.Xr icmp 4 , 333.Xr intro 4 , 334.Xr ip 4 , 335.Xr ipfirewall 4 , 336.Xr route 4 , 337.Xr tcp 4 , 338.Xr udp 4 , 339.Xr sysctl 8 , 340.Xr pfil 9 341.Rs 342.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 343.%B PS1 344.%N 7 345.Re 346.Rs 347.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 348.%B PS1 349.%N 8 350.Re 351.Sh HISTORY 352The 353.Nm 354protocol interface appeared in 355.Bx 4.2 . 356The 357.Dq protocol cloning 358code appeared in 359.Fx 2.1 . 360.Sh CAVEATS 361The Internet protocol support is subject to change as 362the Internet protocols develop. 363Users should not depend 364on details of the current implementation, but rather 365the services exported. 366