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32 .\" From: @(#)inet.4 8.1 (Berkeley) 6/5/93
40 .Nd Internet protocol family
45 The Internet protocol family is a collection of protocols
49 transport layer, and utilizing the Internet address format.
50 The Internet family provides protocol support for the
51 .Dv SOCK_STREAM , SOCK_DGRAM ,
56 interface provides access to the
60 Internet addresses are four byte quantities, stored in
61 network standard format (on little endian machines, such as the
67 these are word and byte reversed).
71 as a discriminated union.
73 Sockets bound to the Internet protocol family utilize
74 the following addressing structure,
75 .Bd -literal -offset indent
78 sa_family_t sin_family;
80 struct in_addr sin_addr;
85 Sockets may be created with the local address
89 matching on incoming messages.
98 The distinguished address
100 is allowed as a shorthand for the broadcast address on the primary
101 network if the first network configured supports broadcast.
103 The Internet protocol family is comprised of
106 network protocol, Internet Control
109 Internet Group Management Protocol
114 and User Datagram Protocol
117 is used to support the
121 is used to support the
127 by creating an Internet socket of type
131 message protocol is accessible from a raw socket.
133 The 32-bit Internet address contains both network and host parts.
134 However, direct examination of addresses is discouraged.
136 programs which absolutely need to break addresses into their component
139 commands are provided for a datagram socket in the Internet domain;
140 they have the same form as the
144 .Bl -tag -width SIOCSIFNETMASK
145 .It Dv SIOCSIFNETMASK
146 Set interface network mask.
147 The network mask defines the network part of the address;
148 if it contains more of the address than the address type would indicate,
149 then subnets are in use.
150 .It Dv SIOCGIFNETMASK
151 Get interface network mask.
154 A number of variables are implemented in the net.inet branch of the
157 In addition to the variables supported by the transport protocols
158 (for which the respective manual pages may be consulted),
159 the following general variables are defined:
160 .Bl -tag -width IPCTL_FASTFORWARDING
161 .It Dv IPCTL_FORWARDING
163 Boolean: enable/disable forwarding of IP packets.
165 .It Dv IPCTL_FASTFORWARDING
166 .Pq ip.fastforwarding
167 Boolean: enable/disable the use of
168 .Tn fast IP forwarding
172 .Tn fast IP forwarding
173 is enabled, IP packets are forwarded directly to the appropriate network
174 interface with direct processing to completion, which greatly improves
176 All packets for local IP addresses, non-unicast, or with IP options are
177 handled by the normal IP input processing path.
178 All features of the normal (slow) IP forwarding path are supported
179 including firewall (through
181 hooks) checking, except
185 .Tn IP fastforwarding
186 path does not generate ICMP redirect or source quench messages.
187 .It Dv IPCTL_SENDREDIRECTS
189 Boolean: enable/disable sending of ICMP redirects in response to
191 packets for which a better, and for the sender directly reachable, route
192 and next hop is known.
196 Integer: default time-to-live
201 .It Dv IPCTL_ACCEPTSOURCEROUTE
202 .Pq ip.accept_sourceroute
203 Boolean: enable/disable accepting of source-routed IP packets (default false).
204 .It Dv IPCTL_SOURCEROUTE
206 Boolean: enable/disable forwarding of source-routed IP packets (default false).
207 .It Dv IPCTL_RTEXPIRE
209 Integer: lifetime in seconds of protocol-cloned
211 routes after the last reference drops (default one hour).
212 This value varies dynamically as described above.
213 .It Dv IPCTL_RTMINEXPIRE
215 Integer: minimum value of ip.rtexpire (default ten seconds).
216 This value has no effect on user modifications, but restricts the dynamic
217 adaptation described above.
218 .It Dv IPCTL_RTMAXCACHE
220 Integer: trigger level of cached, unreferenced, protocol-cloned routes
221 which initiates dynamic adaptation (default 128).
222 .It Va ip.process_options
223 Integer: control IP options processing.
224 By setting this variable to 0, all IP options in the incoming packets
225 will be ignored, and the packets will be passed unmodified.
226 By setting to 1, IP options in the incoming packets will be processed
230 .Dq "prohibited by filter"
231 message will be sent back in response to incoming packets with IP options.
235 variable affects packets destined for a local host as well as packets
236 forwarded to some other host.
238 Boolean: control IP IDs generation behaviour.
241 to non-zero causes the ID field in IP packets to be randomized instead of
242 incremented by 1 with each packet generated.
243 This closes a minor information leak which allows remote observers to
244 determine the rate of packet generation on the machine by watching the
246 In the same time, on high-speed links, it can decrease the ID reuse
248 Default is 0 (sequential IP IDs).
249 IPv6 flow IDs and fragment IDs are always random.
250 .It Va ip.maxfragpackets
251 Integer: maximum number of fragmented packets the host will accept and hold
252 in the reassembling queue simultaneously.
253 0 means that the host will not accept any fragmented packets.
254 \-1 means that the host will accept as many fragmented packets as it receives.
255 .It Va ip.maxfragsperpacket
256 Integer: maximum number of fragments the host will accept and hold
257 in the reassembling queue for a packet.
258 0 means that the host will not accept any fragmented packets.
273 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
278 .%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"
285 protocol interface appeared in
292 The Internet protocol support is subject to change as
293 the Internet protocols develop.
294 Users should not depend
295 on details of the current implementation, but rather
296 the services exported.