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28 .\" From: @(#)inet.4 8.1 (Berkeley) 6/5/93
29 .\" $FreeBSD: src/share/man/man4/inet.4,v 1.11.2.6 2001/12/17 11:30:12 ru Exp $
30 .\" $DragonFly: src/share/man/man4/inet.4,v 1.8 2008/05/02 02:05:05 swildner Exp $
37 .Nd Internet protocol family
42 The Internet protocol family is a collection of protocols
46 transport layer, and utilizing the Internet address format.
47 The Internet family provides protocol support for the
48 .Dv SOCK_STREAM , SOCK_DGRAM ,
53 interface provides access to the
57 Internet addresses are four byte quantities, stored in
58 network standard format (on the
60 these are word and byte
61 reversed). The include file
64 as a discriminated union.
66 Sockets bound to the Internet protocol family utilize
67 the following addressing structure,
68 .Bd -literal -offset indent
73 struct in_addr sin_addr;
78 Sockets may be created with the local address
82 matching on incoming messages.
91 The distinguished address
93 is allowed as a shorthand for the broadcast address on the primary
94 network if the first network configured supports broadcast.
96 The Internet protocol family is comprised of
99 network protocol, Internet Control
102 Internet Group Management Protocol
107 and User Datagram Protocol
110 is used to support the
114 is used to support the
116 abstraction. A raw interface to
119 by creating an Internet socket of type
123 message protocol is accessible from a raw socket.
125 The 32-bit Internet address contains both network and host parts.
126 However, direct examination of addresses is discouraged. For those
127 programs which absolutely need to break addresses into their component
130 commands are provided for a datagram socket in the Internet domain;
131 they have the same form as the
137 .Bl -tag -width ".Dv SIOCSIFNETMASK"
138 .It Dv SIOCSIFNETMASK
139 Set interface network mask.
140 The network mask defines the network part of the address;
141 if it contains more of the address than the address type would indicate,
142 then subnets are in use.
143 .It Dv SIOCGIFNETMASK
144 Get interface network mask.
147 The current implementation of Internet protocols includes some routing-table
148 adaptations to provide enhanced caching of certain end-to-end
149 information necessary for Transaction TCP and Path MTU Discovery. The
150 following changes are the most significant:
153 All IP routes, except those with the
155 flag and those to multicast destinations, have the
157 flag forcibly enabled (they are thus said to be
158 .Dq "protocol cloning" ) .
160 When the last reference to an IP route is dropped, the route is
161 examined to determine if it was created by cloning such a route. If
162 this is the case, the
164 flag is turned on, and the expiration timer is initialized to go off in
165 .Va net.inet.ip.rtexpire
167 If such a route is re-referenced, the flag and expiration timer are reset.
169 A kernel timeout runs once every ten minutes, or sooner if there are
170 soon-to-expire routes in the kernel routing table, and deletes the
174 A dynamic process is in place to modify the value of
175 .Va net.inet.ip.rtexpire
176 if the number of cached routes grows too large.
177 If after an expiration run there are still more than
178 .Va net.inet.ip.rtmaxcache
179 unreferenced routes remaining, the rtexpire
180 value is multiplied by \(34, and any routes which have longer
181 expiration times have those times adjusted. This process is damped
182 somewhat by specification of a minimum rtexpire value
183 .Va ( net.inet.ip.rtminexpire ) ,
184 and by restricting the reduction to once in a ten-minute period.
186 If some external process deletes the original route from which a
187 protocol-cloned route was generated, the ``child route'' is deleted.
188 (This is actually a generic mechanism in the routing code support for
189 protocol-requested cloning.)
191 No attempt is made to manage routes which were not created by protocol
192 cloning; these are assumed to be static, under the management of an
193 external routing process, or under the management of a link layer
198 Only certain types of network activity will result in the cloning of a
199 route using this mechanism. Specifically, those protocols (such as
203 which themselves cache a long-lasting reference to route for a destination
204 will trigger the mechanism; whereas raw
206 packets, whether locally-generated or forwarded, will not.
208 A number of variables are implemented in the net.inet branch of the
211 In addition to the variables supported by the transport protocols
212 (for which the respective manual pages may be consulted),
213 the following general variables are defined:
214 .Bl -tag -width IPCTL_FASTFORWARDING
215 .It Dv IPCTL_FORWARDING
217 Boolean: enable/disable forwarding of IP packets.
219 .It Dv IPCTL_FASTFORWARDING
220 .Pq ip.fastforwarding
221 Boolean: enable/disable the use of fast IP forwarding code.
223 When fast forwarding is enabled, IP packets are forwarded directly to
224 the appropriate network interface with a minimal validity checking, which
225 greatly improves the throughput. On the other hand, they bypass the
226 standard procedures, such as IP option processing and
229 It is not guaranteed that every packet will be fast-forwarded.
230 .It Dv IPCTL_SENDREDIRECTS
232 Boolean: enable/disable sending of ICMP redirects in response to
239 Integer: default time-to-live
244 .It Dv IPCTL_SOURCEROUTE
246 Boolean: enable/disable forwarding of source-routed IP packets (default false).
247 .It Dv IPCTL_RTEXPIRE
249 Integer: lifetime in seconds of protocol-cloned
251 routes after the last reference drops (default one hour). This value
252 varies dynamically as described above.
253 .It Dv IPCTL_RTMINEXPIRE
255 Integer: minimum value of ip.rtexpire (default ten seconds). This
256 value has no effect on user modifications, but restricts the dynamic
257 adaptation described above.
258 .It Dv IPCTL_RTMAXCACHE
260 Integer: trigger level of cached, unreferenced, protocol-cloned routes
261 which initiates dynamic adaptation (default 128).
274 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
279 .%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"
284 The Internet protocol support is subject to change as
285 the Internet protocols develop. Users should not depend
286 on details of the current implementation, but rather
287 the services exported.
291 protocol interface appeared in