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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 reversed).
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
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.
128 programs which absolutely need to break addresses into their component
131 commands are provided for a datagram socket in the Internet domain;
132 they have the same form as the
138 .Bl -tag -width ".Dv SIOCSIFNETMASK"
139 .It Dv SIOCSIFNETMASK
140 Set interface network mask.
141 The network mask defines the network part of the address;
142 if it contains more of the address than the address type would indicate,
143 then subnets are in use.
144 .It Dv SIOCGIFNETMASK
145 Get interface network mask.
148 The current implementation of Internet protocols includes some routing-table
149 adaptations to provide enhanced caching of certain end-to-end
150 information necessary for Transaction TCP and Path MTU Discovery.
151 The following changes are the most significant:
154 All IP routes, except those with the
156 flag and those to multicast destinations, have the
158 flag forcibly enabled (they are thus said to be
159 .Dq "protocol cloning" ) .
161 When the last reference to an IP route is dropped, the route is
162 examined to determine if it was created by cloning such a route.
163 If this is the case, the
165 flag is turned on, and the expiration timer is initialized to go off in
166 .Va net.inet.ip.rtexpire
168 If such a route is re-referenced, the flag and expiration timer are reset.
170 A kernel timeout runs once every ten minutes, or sooner if there are
171 soon-to-expire routes in the kernel routing table, and deletes the
175 A dynamic process is in place to modify the value of
176 .Va net.inet.ip.rtexpire
177 if the number of cached routes grows too large.
178 If after an expiration run there are still more than
179 .Va net.inet.ip.rtmaxcache
180 unreferenced routes remaining, the rtexpire
181 value is multiplied by \(34, and any routes which have longer
182 expiration times have those times adjusted.
183 This process is damped somewhat by specification of a minimum rtexpire value
184 .Va ( net.inet.ip.rtminexpire ) ,
185 and by restricting the reduction to once in a ten-minute period.
187 If some external process deletes the original route from which a
188 protocol-cloned route was generated, the ``child route'' is deleted.
189 (This is actually a generic mechanism in the routing code support for
190 protocol-requested cloning.)
192 No attempt is made to manage routes which were not created by protocol
193 cloning; these are assumed to be static, under the management of an
194 external routing process, or under the management of a link layer
199 Only certain types of network activity will result in the cloning of a
200 route using this mechanism.
201 Specifically, those protocols (such as
205 which themselves cache a long-lasting reference to route for a destination
206 will trigger the mechanism; whereas raw
208 packets, whether locally-generated or forwarded, will not.
210 A number of variables are implemented in the net.inet branch of the
213 In addition to the variables supported by the transport protocols
214 (for which the respective manual pages may be consulted),
215 the following general variables are defined:
216 .Bl -tag -width IPCTL_FASTFORWARDING
217 .It Dv IPCTL_FORWARDING
219 Boolean: enable/disable forwarding of IP packets.
221 .It Dv IPCTL_FASTFORWARDING
222 .Pq ip.fastforwarding
223 Boolean: enable/disable the use of fast IP forwarding code.
225 When fast forwarding is enabled, IP packets are forwarded directly to
226 the appropriate network interface with a minimal validity checking, which
227 greatly improves the throughput.
228 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).
255 This value varies dynamically as described above.
256 .It Dv IPCTL_RTMINEXPIRE
258 Integer: minimum value of ip.rtexpire (default ten seconds).
259 This 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).
277 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
282 .%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"
287 The Internet protocol support is subject to change as
288 the Internet protocols develop.
289 Users should not depend on details of the current implementation, but rather
290 the services exported.
294 protocol interface appeared in