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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 $
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 the
59 these are word and byte
60 reversed). The include file
63 as a discriminated union.
65 Sockets bound to the Internet protocol family utilize
66 the following addressing structure,
67 .Bd -literal -offset indent
70 sa_family_t sin_family;
72 struct in_addr sin_addr;
77 Sockets may be created with the local address
81 matching on incoming messages.
90 The distinguished address
92 is allowed as a shorthand for the broadcast address on the primary
93 network if the first network configured supports broadcast.
95 The Internet protocol family is comprised of
98 network protocol, Internet Control
101 Internet Group Management Protocol
106 and User Datagram Protocol
109 is used to support the
113 is used to support the
115 abstraction. A raw interface to
118 by creating an Internet socket of type
122 message protocol is accessible from a raw socket.
124 The 32-bit Internet address contains both network and host parts.
125 However, direct examination of addresses is discouraged. For those
126 programs which absolutely need to break addresses into their component
129 commands are provided for a datagram socket in the Internet domain;
130 they have the same form as the
136 .Bl -tag -width ".Dv SIOCSIFNETMASK"
137 .It Dv SIOCSIFNETMASK
138 Set interface network mask.
139 The network mask defines the network part of the address;
140 if it contains more of the address than the address type would indicate,
141 then subnets are in use.
142 .It Dv SIOCGIFNETMASK
143 Get interface network mask.
146 The current implementation of Internet protocols includes some routing-table
147 adaptations to provide enhanced caching of certain end-to-end
148 information necessary for Transaction TCP and Path MTU Discovery. The
149 following changes are the most significant:
152 All IP routes, except those with the
154 flag and those to multicast destinations, have the
156 flag forcibly enabled (they are thus said to be
157 .Dq "protocol cloning" ) .
159 When the last reference to an IP route is dropped, the route is
160 examined to determine if it was created by cloning such a route. If
161 this is the case, the
163 flag is turned on, and the expiration timer is initialized to go off in
164 .Va net.inet.ip.rtexpire
166 If such a route is re-referenced, the flag and expiration timer are reset.
168 A kernel timeout runs once every ten minutes, or sooner if there are
169 soon-to-expire routes in the kernel routing table, and deletes the
173 A dynamic process is in place to modify the value of
174 .Va net.inet.ip.rtexpire
175 if the number of cached routes grows too large.
176 If after an expiration run there are still more than
177 .Va net.inet.ip.rtmaxcache
178 unreferenced routes remaining, the rtexpire
179 value is multiplied by \(34, and any routes which have longer
180 expiration times have those times adjusted. This process is damped
181 somewhat by specification of a minimum rtexpire value
182 .Va ( net.inet.ip.rtminexpire ) ,
183 and by restricting the reduction to once in a ten-minute period.
185 If some external process deletes the original route from which a
186 protocol-cloned route was generated, the ``child route'' is deleted.
187 (This is actually a generic mechanism in the routing code support for
188 protocol-requested cloning.)
190 No attempt is made to manage routes which were not created by protocol
191 cloning; these are assumed to be static, under the management of an
192 external routing process, or under the management of a link layer
197 Only certain types of network activity will result in the cloning of a
198 route using this mechanism. Specifically, those protocols (such as
202 which themselves cache a long-lasting reference to route for a destination
203 will trigger the mechanism; whereas raw
205 packets, whether locally-generated or forwarded, will not.
207 A number of variables are implemented in the net.inet branch of the
210 In addition to the variables supported by the transport protocols
211 (for which the respective manual pages may be consulted),
212 the following general variables are defined:
213 .Bl -tag -width IPCTL_FASTFORWARDING
214 .It Dv IPCTL_FORWARDING
216 Boolean: enable/disable forwarding of IP packets.
218 .It Dv IPCTL_FASTFORWARDING
219 .Pq ip.fastforwarding
220 Boolean: enable/disable the use of fast IP forwarding code.
222 When fast forwarding is enabled, IP packets are forwarded directly to
223 the appropriate network interface with a minimal validity checking, which
224 greatly improves the throughput. On the other hand, they bypass the
225 standard procedures, such as IP option processing and
228 It is not guaranteed that every packet will be fast-forwarded.
229 .It Dv IPCTL_SENDREDIRECTS
231 Boolean: enable/disable sending of ICMP redirects in response to
238 Integer: default time-to-live
243 .It Dv IPCTL_SOURCEROUTE
245 Boolean: enable/disable forwarding of source-routed IP packets (default false).
246 .It Dv IPCTL_RTEXPIRE
248 Integer: lifetime in seconds of protocol-cloned
250 routes after the last reference drops (default one hour). This value
251 varies dynamically as described above.
252 .It Dv IPCTL_RTMINEXPIRE
254 Integer: minimum value of ip.rtexpire (default ten seconds). This
255 value has no effect on user modifications, but restricts the dynamic
256 adaptation described above.
257 .It Dv IPCTL_RTMAXCACHE
259 Integer: trigger level of cached, unreferenced, protocol-cloned routes
260 which initiates dynamic adaptation (default 128).
273 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
278 .%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"
283 The Internet protocol support is subject to change as
284 the Internet protocols develop. Users should not depend
285 on details of the current implementation, but rather
286 the services exported.
290 protocol interface appeared in