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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.
135 address on an interface consist of the address itself, the
136 netmask, either broadcast address in case of a broadcast
137 interface or peers address in case of point-to-point interface.
140 commands are provided for a datagram socket in the Internet domain:
142 .Bl -tag -width ".Dv SIOCGIFBRDADDR" -offset indent -compact
144 Add address to an interface.
146 .Ft struct in_aliasreq
149 Delete address from an interface.
154 .It Dv SIOCGIFBRDADDR
155 .It Dv SIOCGIFDSTADDR
156 .It Dv SIOCGIFNETMASK
157 Return address information from interface. The returned value
160 This way of address information retrieval is obsoleted, a
161 preferred way is to use
166 A number of variables are implemented in the net.inet branch of the
169 In addition to the variables supported by the transport protocols
170 (for which the respective manual pages may be consulted),
171 the following general variables are defined:
172 .Bl -tag -width IPCTL_FASTFORWARDING
173 .It Dv IPCTL_FORWARDING
175 Boolean: enable/disable forwarding of IP packets.
177 .It Dv IPCTL_FASTFORWARDING
178 .Pq ip.fastforwarding
179 Boolean: enable/disable the use of
180 .Tn fast IP forwarding
184 .Tn fast IP forwarding
185 is enabled, IP packets are forwarded directly to the appropriate network
186 interface with direct processing to completion, which greatly improves
188 All packets for local IP addresses, non-unicast, or with IP options are
189 handled by the normal IP input processing path.
190 All features of the normal (slow) IP forwarding path are supported
191 including firewall (through
193 hooks) checking, except
197 .Tn IP fastforwarding
198 path does not generate ICMP redirect or source quench messages.
199 .It Dv IPCTL_SENDREDIRECTS
201 Boolean: enable/disable sending of ICMP redirects in response to
203 packets for which a better, and for the sender directly reachable, route
204 and next hop is known.
208 Integer: default time-to-live
213 .It Dv IPCTL_ACCEPTSOURCEROUTE
214 .Pq ip.accept_sourceroute
215 Boolean: enable/disable accepting of source-routed IP packets (default false).
216 .It Dv IPCTL_SOURCEROUTE
218 Boolean: enable/disable forwarding of source-routed IP packets (default false).
219 .It Dv IPCTL_RTEXPIRE
221 Integer: lifetime in seconds of protocol-cloned
223 routes after the last reference drops (default one hour).
224 This value varies dynamically as described above.
225 .It Dv IPCTL_RTMINEXPIRE
227 Integer: minimum value of ip.rtexpire (default ten seconds).
228 This value has no effect on user modifications, but restricts the dynamic
229 adaptation described above.
230 .It Dv IPCTL_RTMAXCACHE
232 Integer: trigger level of cached, unreferenced, protocol-cloned routes
233 which initiates dynamic adaptation (default 128).
234 .It Va ip.process_options
235 Integer: control IP options processing.
236 By setting this variable to 0, all IP options in the incoming packets
237 will be ignored, and the packets will be passed unmodified.
238 By setting to 1, IP options in the incoming packets will be processed
242 .Dq "prohibited by filter"
243 message will be sent back in response to incoming packets with IP options.
247 variable affects packets destined for a local host as well as packets
248 forwarded to some other host.
250 Boolean: control IP IDs generation behaviour.
253 to non-zero causes the ID field in IP packets to be randomized instead of
254 incremented by 1 with each packet generated.
255 This closes a minor information leak which allows remote observers to
256 determine the rate of packet generation on the machine by watching the
258 In the same time, on high-speed links, it can decrease the ID reuse
260 Default is 0 (sequential IP IDs).
261 IPv6 flow IDs and fragment IDs are always random.
262 .It Va ip.maxfragpackets
263 Integer: maximum number of fragmented packets the host will accept and hold
264 in the reassembling queue simultaneously.
265 0 means that the host will not accept any fragmented packets.
266 \-1 means that the host will accept as many fragmented packets as it receives.
267 .It Va ip.maxfragsperpacket
268 Integer: maximum number of fragments the host will accept and hold
269 in the reassembling queue for a packet.
270 0 means that the host will not accept any fragmented packets.
286 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
291 .%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"
298 protocol interface appeared in
305 The Internet protocol support is subject to change as
306 the Internet protocols develop.
307 Users should not depend
308 on details of the current implementation, but rather
309 the services exported.