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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 November 12, 2021 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 161A number of variables are implemented in the net.inet branch of the 162.Xr sysctl 3 163MIB. 164In addition to the variables supported by the transport protocols 165(for which the respective manual pages may be consulted), 166the following general variables are defined: 167.Bl -tag -width IPCTL_ACCEPTSOURCEROUTE 168.It Dv IPCTL_FORWARDING 169.Pq ip.forwarding 170Boolean: enable/disable forwarding of IP packets. 171Defaults to off. 172.It Dv IPCTL_SENDREDIRECTS 173.Pq ip.redirect 174Boolean: enable/disable sending of ICMP redirects in response to 175.Tn IP 176packets for which a better, and for the sender directly reachable, route 177and next hop is known. 178Defaults to on. 179.It Dv IPCTL_DEFTTL 180.Pq ip.ttl 181Integer: default time-to-live 182.Pq Dq TTL 183to use for outgoing 184.Tn IP 185packets. 186.It Dv IPCTL_ACCEPTSOURCEROUTE 187.Pq ip.accept_sourceroute 188Boolean: enable/disable accepting of source-routed IP packets (default false). 189.It Dv IPCTL_SOURCEROUTE 190.Pq ip.sourceroute 191Boolean: enable/disable forwarding of source-routed IP packets (default false). 192.It Va ip.process_options 193Integer: control IP options processing. 194By setting this variable to 0, all IP options in the incoming packets 195will be ignored, and the packets will be passed unmodified. 196By setting to 1, IP options in the incoming packets will be processed 197accordingly. 198By setting to 2, an 199.Tn ICMP 200.Dq "prohibited by filter" 201message will be sent back in response to incoming packets with IP options. 202Default is 1. 203This 204.Xr sysctl 8 205variable affects packets destined for a local host as well as packets 206forwarded to some other host. 207.It Va ip.rfc1122_strong_es 208Boolean: in non-forwarding mode 209.Pq ip.forwarding is disabled 210partially implement the Strong End System model per RFC1122. 211If a packet with destination address that is local arrives on a different 212interface than the interface the address belongs to, the packet would be 213silently dropped. 214Enabling this option may break certain setups, e.g. having an alias address(es) 215on loopback that are expected to be reachable by outside traffic. 216Enabling some other network features, e.g. 217.Xr carp 4 218or destination address rewriting 219.Xr pfil 4 220filters may override and bypass this check. 221Disabled by default. 222.It Va ip.source_address_validation 223Boolean: perform source address validation for packets destined for the local 224host. 225Consider this as following Section 3.2 of RFC3704/BCP84, where we treat local 226host as our own infrastructure. 227This has no effect on packets to be forwarded, so don't consider it as 228anti-spoof feature for a router. 229Enabled by default. 230.It Va ip.rfc6864 231Boolean: control IP IDs generation behaviour. 232True value enables RFC6864 support, which specifies that IP ID field of 233.Em atomic 234datagrams can be set to any value. 235The 236.Fx implementation sets it to zero. 237Enabled by default. 238.It Va ip.random_id 239Boolean: control IP IDs generation behaviour. 240Setting this 241.Xr sysctl 8 242to 1 causes the ID field in 243.Em non-atomic 244IP datagrams (or all IP datagrams, if 245.Va ip.rfc6864 246is disabled) to be randomized instead of incremented by 1 with each packet 247generated. 248This closes a minor information leak which allows remote observers to 249determine the rate of packet generation on the machine by watching the 250counter. 251At the same time, on high-speed links, it can decrease the ID reuse 252cycle greatly. 253Default is 0 (sequential IP IDs). 254IPv6 flow IDs and fragment IDs are always random. 255.It Va ip.maxfrags 256Integer: maximum number of fragments the host will accept and simultaneously 257hold across all reassembly queues in all VNETs. 258If set to 0, reassembly is disabled. 259If set to -1, this limit is not applied. 260This limit is recalculated when the number of mbuf clusters is changed. 261This is a global limit. 262.It Va ip.maxfragpackets 263Integer: maximum number of fragmented packets the host will accept and 264simultaneously hold in the reassembly queue for a particular VNET. 2650 means that the host will not accept any fragmented packets for that VNET. 266\-1 means that the host will not apply this limit for that VNET. 267This limit is recalculated when the number of mbuf clusters is changed. 268This is a per-VNET limit. 269.It Va ip.maxfragbucketsize 270Integer: maximum number of reassembly queues per bucket. 271Fragmented packets are hashed to buckets. 272Each bucket has a list of reassembly queues. 273The system must compare the incoming packets to the existing reassembly queues 274in the bucket to find a matching reassembly queue. 275To preserve system resources, the system limits the number of reassembly 276queues allowed in each bucket. 277This limit is recalculated when the number of mbuf clusters is changed or 278when the value of 279.Va ip.maxfragpackets 280changes. 281This is a per-VNET limit. 282.It Va ip.maxfragsperpacket 283Integer: maximum number of fragments the host will accept and hold 284in the reassembly queue for a packet. 2850 means that the host will not accept any fragmented packets for the VNET. 286This is a per-VNET limit. 287.El 288.Sh SEE ALSO 289.Xr ioctl 2 , 290.Xr socket 2 , 291.Xr getifaddrs 3 , 292.Xr sysctl 3 , 293.Xr icmp 4 , 294.Xr intro 4 , 295.Xr ip 4 , 296.Xr ipfirewall 4 , 297.Xr route 4 , 298.Xr tcp 4 , 299.Xr udp 4 , 300.Xr pfil 9 301.Rs 302.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 303.%B PS1 304.%N 7 305.Re 306.Rs 307.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 308.%B PS1 309.%N 8 310.Re 311.Sh HISTORY 312The 313.Nm 314protocol interface appeared in 315.Bx 4.2 . 316The 317.Dq protocol cloning 318code appeared in 319.Fx 2.1 . 320.Sh CAVEATS 321The Internet protocol support is subject to change as 322the Internet protocols develop. 323Users should not depend 324on details of the current implementation, but rather 325the services exported. 326