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28 .\" From: @(#)inet.4 8.1 (Berkeley) 6/5/93
36 .Nd Internet protocol family
41 The Internet protocol family is a collection of protocols
45 transport layer, and utilizing the Internet address format.
46 The Internet family provides protocol support for the
47 .Dv SOCK_STREAM , SOCK_DGRAM ,
52 interface provides access to the
56 Internet addresses are four byte quantities, stored in
57 network standard format (on little endian machines, such as the
63 these are word and byte reversed).
67 as a discriminated union.
69 Sockets bound to the Internet protocol family utilize
70 the following addressing structure,
71 .Bd -literal -offset indent
74 sa_family_t sin_family;
76 struct in_addr sin_addr;
81 Sockets may be created with the local address
85 matching on incoming messages.
94 The distinguished address
96 is allowed as a shorthand for the broadcast address on the primary
97 network if the first network configured supports broadcast.
99 The Internet protocol family is comprised of
102 network protocol, Internet Control
105 Internet Group Management Protocol
110 and User Datagram Protocol
113 is used to support the
117 is used to support the
123 by creating an Internet socket of type
127 message protocol is accessible from a raw socket.
131 address on an interface consist of the address itself, the
132 netmask, either broadcast address in case of a broadcast
133 interface or peers address in case of point-to-point interface.
136 commands are provided for a datagram socket in the Internet domain:
138 .Bl -tag -width ".Dv SIOCGIFBRDADDR" -offset indent -compact
140 Add address to an interface.
142 .Ft struct in_aliasreq
145 Delete address from an interface.
150 .It Dv SIOCGIFBRDADDR
151 .It Dv SIOCGIFDSTADDR
152 .It Dv SIOCGIFNETMASK
153 Return address information from interface. The returned value
156 This way of address information retrieval is obsoleted, a
157 preferred way is to use
162 A number of variables are implemented in the net.inet branch of the
165 In addition to the variables supported by the transport protocols
166 (for which the respective manual pages may be consulted),
167 the following general variables are defined:
168 .Bl -tag -width IPCTL_FASTFORWARDING
169 .It Dv IPCTL_FORWARDING
171 Boolean: enable/disable forwarding of IP packets.
173 .It Dv IPCTL_FASTFORWARDING
174 .Pq ip.fastforwarding
175 Boolean: enable/disable the use of
176 .Tn fast IP forwarding
180 .Tn fast IP forwarding
181 is enabled, IP packets are forwarded directly to the appropriate network
182 interface with direct processing to completion, which greatly improves
184 All packets for local IP addresses, non-unicast, or with IP options are
185 handled by the normal IP input processing path.
186 All features of the normal (slow) IP forwarding path are supported
187 including firewall (through
189 hooks) checking, except
193 .Tn IP fastforwarding
194 path does not generate ICMP redirect or source quench messages.
195 .It Dv IPCTL_SENDREDIRECTS
197 Boolean: enable/disable sending of ICMP redirects in response to
199 packets for which a better, and for the sender directly reachable, route
200 and next hop is known.
204 Integer: default time-to-live
209 .It Dv IPCTL_ACCEPTSOURCEROUTE
210 .Pq ip.accept_sourceroute
211 Boolean: enable/disable accepting of source-routed IP packets (default false).
212 .It Dv IPCTL_SOURCEROUTE
214 Boolean: enable/disable forwarding of source-routed IP packets (default false).
215 .It Dv IPCTL_RTEXPIRE
217 Integer: lifetime in seconds of protocol-cloned
219 routes after the last reference drops (default one hour).
220 This value varies dynamically as described above.
221 .It Dv IPCTL_RTMINEXPIRE
223 Integer: minimum value of ip.rtexpire (default ten seconds).
224 This value has no effect on user modifications, but restricts the dynamic
225 adaptation described above.
226 .It Dv IPCTL_RTMAXCACHE
228 Integer: trigger level of cached, unreferenced, protocol-cloned routes
229 which initiates dynamic adaptation (default 128).
230 .It Va ip.process_options
231 Integer: control IP options processing.
232 By setting this variable to 0, all IP options in the incoming packets
233 will be ignored, and the packets will be passed unmodified.
234 By setting to 1, IP options in the incoming packets will be processed
238 .Dq "prohibited by filter"
239 message will be sent back in response to incoming packets with IP options.
243 variable affects packets destined for a local host as well as packets
244 forwarded to some other host.
246 Boolean: control IP IDs generation behaviour.
249 to non-zero causes the ID field in IP packets to be randomized instead of
250 incremented by 1 with each packet generated.
251 This closes a minor information leak which allows remote observers to
252 determine the rate of packet generation on the machine by watching the
254 In the same time, on high-speed links, it can decrease the ID reuse
256 Default is 0 (sequential IP IDs).
257 IPv6 flow IDs and fragment IDs are always random.
258 .It Va ip.maxfragpackets
259 Integer: maximum number of fragmented packets the host will accept and hold
260 in the reassembling queue simultaneously.
261 0 means that the host will not accept any fragmented packets.
262 \-1 means that the host will accept as many fragmented packets as it receives.
263 .It Va ip.maxfragsperpacket
264 Integer: maximum number of fragments the host will accept and hold
265 in the reassembling queue for a packet.
266 0 means that the host will not accept any fragmented packets.
282 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
287 .%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"
294 protocol interface appeared in
301 The Internet protocol support is subject to change as
302 the Internet protocols develop.
303 Users should not depend
304 on details of the current implementation, but rather
305 the services exported.