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32 .\" From: @(#)inet.4 8.1 (Berkeley) 6/5/93
33 .\" $FreeBSD: src/share/man/man4/inet.4,v 1.11.2.6 2001/12/17 11:30:12 ru Exp $
34 .\" $DragonFly: src/share/man/man4/inet.4,v 1.6 2007/11/04 19:04:42 swildner Exp $
41 .Nd Internet protocol family
46 The Internet protocol family is a collection of protocols
50 transport layer, and utilizing the Internet address format.
51 The Internet family provides protocol support for the
52 .Dv SOCK_STREAM , SOCK_DGRAM ,
57 interface provides access to the
61 Internet addresses are four byte quantities, stored in
62 network standard format (on the
64 these are word and byte
65 reversed). The include file
68 as a discriminated union.
70 Sockets bound to the Internet protocol family utilize
71 the following addressing structure,
72 .Bd -literal -offset indent
77 struct in_addr sin_addr;
82 Sockets may be created with the local address
86 matching on incoming messages.
95 The distinguished address
97 is allowed as a shorthand for the broadcast address on the primary
98 network if the first network configured supports broadcast.
100 The Internet protocol family is comprised of
103 network protocol, Internet Control
106 Internet Group Management Protocol
111 and User Datagram Protocol
114 is used to support the
118 is used to support the
120 abstraction. A raw interface to
123 by creating an Internet socket of type
127 message protocol is accessible from a raw socket.
129 The 32-bit Internet address contains both network and host parts.
130 However, direct examination of addresses is discouraged. For those
131 programs which absolutely need to break addresses into their component
134 commands are provided for a datagram socket in the Internet domain;
135 they have the same form as the
140 .Bl -tag -width ".Dv SIOCSIFNETMASK"
141 .It Dv SIOCSIFNETMASK
142 Set interface network mask.
143 The network mask defines the network part of the address;
144 if it contains more of the address than the address type would indicate,
145 then subnets are in use.
146 .It Dv SIOCGIFNETMASK
147 Get interface network mask.
150 The current implementation of Internet protocols includes some routing-table
151 adaptations to provide enhanced caching of certain end-to-end
152 information necessary for Transaction TCP and Path MTU Discovery. The
153 following changes are the most significant:
156 All IP routes, except those with the
158 flag and those to multicast destinations, have the
160 flag forcibly enabled (they are thus said to be
161 .Dq "protocol cloning" ) .
163 When the last reference to an IP route is dropped, the route is
164 examined to determine if it was created by cloning such a route. If
165 this is the case, the
167 flag is turned on, and the expiration timer is initialized to go off in
168 .Va net.inet.ip.rtexpire
170 If such a route is re-referenced, the flag and expiration timer are reset.
172 A kernel timeout runs once every ten minutes, or sooner if there are
173 soon-to-expire routes in the kernel routing table, and deletes the
177 A dynamic process is in place to modify the value of
178 .Va net.inet.ip.rtexpire
179 if the number of cached routes grows too large.
180 If after an expiration run there are still more than
181 .Va net.inet.ip.rtmaxcache
182 unreferenced routes remaining, the rtexpire
183 value is multiplied by \(34, and any routes which have longer
184 expiration times have those times adjusted. This process is damped
185 somewhat by specification of a minimum rtexpire value
186 .Va ( net.inet.ip.rtminexpire ) ,
187 and by restricting the reduction to once in a ten-minute period.
189 If some external process deletes the original route from which a
190 protocol-cloned route was generated, the ``child route'' is deleted.
191 (This is actually a generic mechanism in the routing code support for
192 protocol-requested cloning.)
194 No attempt is made to manage routes which were not created by protocol
195 cloning; these are assumed to be static, under the management of an
196 external routing process, or under the management of a link layer
201 Only certain types of network activity will result in the cloning of a
202 route using this mechanism. Specifically, those protocols (such as
206 which themselves cache a long-lasting reference to route for a destination
207 will trigger the mechanism; whereas raw
209 packets, whether locally-generated or forwarded, will not.
211 A number of variables are implemented in the net.inet branch of the
214 In addition to the variables supported by the transport protocols
215 (for which the respective manual pages may be consulted),
216 the following general variables are defined:
217 .Bl -tag -width IPCTL_FASTFORWARDING
218 .It Dv IPCTL_FORWARDING
220 Boolean: enable/disable forwarding of IP packets.
222 .It Dv IPCTL_FASTFORWARDING
223 .Pq ip.fastforwarding
224 Boolean: enable/disable the use of fast IP forwarding code.
226 When fast forwarding is enabled, IP packets are forwarded directly to
227 the appropriate network interface with a minimal validity checking, which
228 greatly improves the throughput. On the other hand, they bypass the
229 standard procedures, such as IP option processing and
232 It is not guaranteed that every packet will be fast-forwarded.
233 .It Dv IPCTL_SENDREDIRECTS
235 Boolean: enable/disable sending of ICMP redirects in response to
242 Integer: default time-to-live
247 .It Dv IPCTL_SOURCEROUTE
249 Boolean: enable/disable forwarding of source-routed IP packets (default false).
250 .It Dv IPCTL_RTEXPIRE
252 Integer: lifetime in seconds of protocol-cloned
254 routes after the last reference drops (default one hour). This value
255 varies dynamically as described above.
256 .It Dv IPCTL_RTMINEXPIRE
258 Integer: minimum value of ip.rtexpire (default ten seconds). This
259 value has no effect on user modifications, but restricts the dynamic
260 adaptation described above.
261 .It Dv IPCTL_RTMAXCACHE
263 Integer: trigger level of cached, unreferenced, protocol-cloned routes
264 which initiates dynamic adaptation (default 128).
278 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
283 .%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"
288 The Internet protocol support is subject to change as
289 the Internet protocols develop. Users should not depend
290 on details of the current implementation, but rather
291 the services exported.
295 protocol interface appeared in