xref: /freebsd/share/man/man4/inet.4 (revision ee7b0571c2c18bdec848ed2044223cc88db29bd8)
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28.\"     From: @(#)inet.4	8.1 (Berkeley) 6/5/93
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31.Dd January 26, 2012
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. The returned value
153is 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_FASTFORWARDING
168.It Dv IPCTL_FORWARDING
169.Pq ip.forwarding
170Boolean: enable/disable forwarding of IP packets.
171Defaults to off.
172.It Dv IPCTL_FASTFORWARDING
173.Pq ip.fastforwarding
174Boolean: enable/disable the use of
175.Tn fast IP forwarding
176code.
177Defaults to off.
178When
179.Tn fast IP forwarding
180is enabled, IP packets are forwarded directly to the appropriate network
181interface with direct processing to completion, which greatly improves
182the throughput.
183All packets for local IP addresses, non-unicast, or with IP options are
184handled by the normal IP input processing path.
185All features of the normal (slow) IP forwarding path are supported
186including firewall (through
187.Xr pfil 9
188hooks) checking, except
189.Xr ipsec 4
190tunnel brokering.
191The
192.Tn IP fastforwarding
193path does not generate ICMP redirect or source quench messages.
194.It Dv IPCTL_SENDREDIRECTS
195.Pq ip.redirect
196Boolean: enable/disable sending of ICMP redirects in response to
197.Tn IP
198packets for which a better, and for the sender directly reachable, route
199and next hop is known.
200Defaults to on.
201.It Dv IPCTL_DEFTTL
202.Pq ip.ttl
203Integer: default time-to-live
204.Pq Dq TTL
205to use for outgoing
206.Tn IP
207packets.
208.It Dv IPCTL_ACCEPTSOURCEROUTE
209.Pq ip.accept_sourceroute
210Boolean: enable/disable accepting of source-routed IP packets (default false).
211.It Dv IPCTL_SOURCEROUTE
212.Pq ip.sourceroute
213Boolean: enable/disable forwarding of source-routed IP packets (default false).
214.It Dv IPCTL_RTEXPIRE
215.Pq ip.rtexpire
216Integer: lifetime in seconds of protocol-cloned
217.Tn IP
218routes after the last reference drops (default one hour).
219This value varies dynamically as described above.
220.It Dv IPCTL_RTMINEXPIRE
221.Pq ip.rtminexpire
222Integer: minimum value of ip.rtexpire (default ten seconds).
223This value has no effect on user modifications, but restricts the dynamic
224adaptation described above.
225.It Dv IPCTL_RTMAXCACHE
226.Pq ip.rtmaxcache
227Integer: trigger level of cached, unreferenced, protocol-cloned routes
228which initiates dynamic adaptation (default 128).
229.It Va ip.process_options
230Integer: control IP options processing.
231By setting this variable to 0, all IP options in the incoming packets
232will be ignored, and the packets will be passed unmodified.
233By setting to 1, IP options in the incoming packets will be processed
234accordingly.
235By setting to 2, an
236.Tn ICMP
237.Dq "prohibited by filter"
238message will be sent back in response to incoming packets with IP options.
239Default is 1.
240This
241.Xr sysctl 8
242variable affects packets destined for a local host as well as packets
243forwarded to some other host.
244.It Va ip.random_id
245Boolean: control IP IDs generation behaviour.
246Setting this
247.Xr sysctl 8
248to non-zero causes the ID field in IP packets to be randomized instead of
249incremented by 1 with each packet generated.
250This closes a minor information leak which allows remote observers to
251determine the rate of packet generation on the machine by watching the
252counter.
253In the same time, on high-speed links, it can decrease the ID reuse
254cycle greatly.
255Default is 0 (sequential IP IDs).
256IPv6 flow IDs and fragment IDs are always random.
257.It Va ip.maxfragpackets
258Integer: maximum number of fragmented packets the host will accept and hold
259in the reassembling queue simultaneously.
2600 means that the host will not accept any fragmented packets.
261\-1 means that the host will accept as many fragmented packets as it receives.
262.It Va ip.maxfragsperpacket
263Integer: maximum number of fragments the host will accept and hold
264in the reassembling queue for a packet.
2650 means that the host will not accept any fragmented packets.
266.El
267.Sh SEE ALSO
268.Xr ioctl 2 ,
269.Xr socket 2 ,
270.Xr getifaddrs 3 ,
271.Xr sysctl 3 ,
272.Xr icmp 4 ,
273.Xr intro 4 ,
274.Xr ip 4 ,
275.Xr ipfirewall 4 ,
276.Xr route 4 ,
277.Xr tcp 4 ,
278.Xr udp 4 ,
279.Xr pfil 9
280.Rs
281.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
282.%B PS1
283.%N 7
284.Re
285.Rs
286.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"
287.%B PS1
288.%N 8
289.Re
290.Sh HISTORY
291The
292.Nm
293protocol interface appeared in
294.Bx 4.2 .
295The
296.Dq protocol cloning
297code appeared in
298.Fx 2.1 .
299.Sh CAVEATS
300The Internet protocol support is subject to change as
301the Internet protocols develop.
302Users should not depend
303on details of the current implementation, but rather
304the services exported.
305