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<table class="head">
<tr>
<td class="head-ltitle">NETINTRO(4)</td>
<td class="head-vol">Device Drivers Manual</td>
<td class="head-rtitle">NETINTRO(4)</td>
</tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp"><code class="Nm">networking</code> —
<span class="Nd">introduction to networking facilities</span></p>
</section>
<section class="Sh">
<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1>
<p class="Pp"><code class="In">#include
<<a class="In">sys/types.h</a>></code>
<br/>
<code class="In">#include <<a class="In">sys/time.h</a>></code>
<br/>
<code class="In">#include <<a class="In">sys/socket.h</a>></code>
<br/>
<code class="In">#include <<a class="In">net/if.h</a>></code>
<br/>
<code class="In">#include <<a class="In">net/route.h</a>></code></p>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp">This section is a general introduction to the networking
facilities available in the system. Documentation in this part of section 4
is broken up into three areas: <i class="Em">protocol families</i>
(domains),
<a class="permalink" href="#protocols"><i class="Em" id="protocols">protocols</i></a>,
and <a class="permalink" href="#network"><i class="Em" id="network">network
interfaces</i></a>.</p>
<p class="Pp">All network protocols are associated with a specific
<i class="Em">protocol family</i>. A protocol family provides basic services
to the protocol implementation to allow it to function within a specific
network environment. These services may include packet fragmentation and
reassembly, routing, addressing, and basic transport. A protocol family may
support multiple methods of addressing, though the current protocol
implementations do not. A protocol family is normally comprised of a number
of protocols, one per <a class="Xr">socket(2)</a> type. It is not required
that a protocol family support all socket types. A protocol family may
contain multiple protocols supporting the same socket abstraction.</p>
<p class="Pp">A protocol supports one of the socket abstractions detailed in
<a class="Xr">socket(2)</a>. A specific protocol may be accessed either by
creating a socket of the appropriate type and protocol family, or by
requesting the protocol explicitly when creating a socket. Protocols
normally accept only one type of address format, usually determined by the
addressing structure inherent in the design of the protocol family/network
architecture. Certain semantics of the basic socket abstractions are
protocol specific. All protocols are expected to support the basic model for
their particular socket type, but may, in addition, provide non-standard
facilities or extensions to a mechanism. For example, a protocol supporting
the <code class="Dv">SOCK_STREAM</code> abstraction may allow more than one
byte of out-of-band data to be transmitted per out-of-band message.</p>
<p class="Pp">A network interface is similar to a device interface. Network
interfaces comprise the lowest layer of the networking subsystem,
interacting with the actual transport hardware. An interface may support one
or more protocol families and/or address formats. The SYNOPSIS section of
each network interface entry gives a sample specification of the related
drivers for use in providing a system description to the
<a class="Xr">config(8)</a> program. The DIAGNOSTICS section lists messages
which may appear on the console and/or in the system error log,
<span class="Pa">/var/log/messages</span> (see
<a class="Xr">syslogd(8)</a>), due to errors in device operation.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="PROTOCOLS"><a class="permalink" href="#PROTOCOLS">PROTOCOLS</a></h1>
<p class="Pp">The system currently supports the Internet protocols, the Xerox
Network Systems(tm) protocols, and some of the ISO OSI protocols. Raw socket
interfaces are provided to the IP protocol layer of the Internet, and to the
IDP protocol of Xerox NS. Consult the appropriate manual pages in this
section for more information regarding the support for each protocol
family.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="ADDRESSING"><a class="permalink" href="#ADDRESSING">ADDRESSING</a></h1>
<p class="Pp">Associated with each protocol family is an address format. All
network addresses adhere to a general structure, called a sockaddr,
described below. However, each protocol imposes finer and more specific
structure, generally renaming the variant, which is discussed in the
protocol family manual page alluded to above.</p>
<div class="Bd Pp Bd-indent Li">
<pre>struct sockaddr {
u_char sa_len;
u_char sa_family;
char sa_data[14];
};</pre>
</div>
<p class="Pp">The field <var class="Va">sa_len</var> contains the total length
of the structure, which may exceed 16 bytes. The following address values
for <var class="Va">sa_family</var> are known to the system (and additional
formats are defined for possible future implementation):</p>
<div class="Bd Pp Li">
<pre>#define AF_UNIX 1 /* local to host (pipes, portals) */
#define AF_INET 2 /* internetwork: UDP, TCP, etc. */
#define AF_NS 6 /* Xerox NS protocols */
#define AF_CCITT 10 /* CCITT protocols, X.25 etc */
#define AF_HYLINK 15 /* NSC Hyperchannel */
#define AF_ISO 18 /* ISO protocols */</pre>
</div>
</section>
<section class="Sh">
<h1 class="Sh" id="ROUTING"><a class="permalink" href="#ROUTING">ROUTING</a></h1>
<p class="Pp"><span class="Ux">FreeBSD</span> provides some packet routing
facilities. The kernel maintains a routing information database, which is
used in selecting the appropriate network interface when transmitting
packets.</p>
<p class="Pp">A user process (or possibly multiple co-operating processes)
maintains this database by sending messages over a special kind of socket.
This supplants fixed size <a class="Xr">ioctl(2)</a> used in earlier
releases.</p>
<p class="Pp">This facility is described in <a class="Xr">route(4)</a>.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="INTERFACES"><a class="permalink" href="#INTERFACES">INTERFACES</a></h1>
<p class="Pp">Each network interface in a system corresponds to a path through
which messages may be sent and received. A network interface usually has a
hardware device associated with it, though certain interfaces such as the
loopback interface, <a class="Xr">lo(4)</a>, do not.</p>
<p class="Pp" id="ioctl">The following <a class="Xr">ioctl(2)</a> calls may be
used to manipulate network interfaces. The
<a class="permalink" href="#ioctl"><code class="Fn">ioctl</code></a>() is
made on a socket (typically of type <code class="Dv">SOCK_DGRAM</code>) in
the desired domain. Most of the requests supported in earlier releases take
an <var class="Vt">ifreq</var> structure as its parameter. This structure
has the form</p>
<div class="Bd Pp Li">
<pre>struct ifreq {
#define IFNAMSIZ 16
char ifr_name[IFNAMSIZ]; /* if name, e.g. "en0" */
union {
struct sockaddr ifru_addr;
struct sockaddr ifru_dstaddr;
struct sockaddr ifru_broadaddr;
struct ifreq_buffer ifru_buffer;
short ifru_flags[2];
short ifru_index;
int ifru_metric;
int ifru_mtu;
int ifru_phys;
int ifru_media;
caddr_t ifru_data;
int ifru_cap[2];
} ifr_ifru;
#define ifr_addr ifr_ifru.ifru_addr /* address */
#define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-to-p link */
#define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
#define ifr_buffer ifr_ifru.ifru_buffer /* user supplied buffer with its length */
#define ifr_flags ifr_ifru.ifru_flags[0] /* flags (low 16 bits) */
#define ifr_flagshigh ifr_ifru.ifru_flags[1] /* flags (high 16 bits) */
#define ifr_metric ifr_ifru.ifru_metric /* metric */
#define ifr_mtu ifr_ifru.ifru_mtu /* mtu */
#define ifr_phys ifr_ifru.ifru_phys /* physical wire */
#define ifr_media ifr_ifru.ifru_media /* physical media */
#define ifr_data ifr_ifru.ifru_data /* for use by interface */
#define ifr_reqcap ifr_ifru.ifru_cap[0] /* requested capabilities */
#define ifr_curcap ifr_ifru.ifru_cap[1] /* current capabilities */
#define ifr_index ifr_ifru.ifru_index /* interface index */
};</pre>
</div>
<p class="Pp" id="Ioctl"><a class="permalink" href="#Ioctl"><code class="Fn">Ioctl</code></a>()
requests to obtain addresses and requests both to set and retrieve other
data are still fully supported and use the <var class="Vt">ifreq</var>
structure:</p>
<dl class="Bl-tag">
<dt id="SIOCGIFADDR"><a class="permalink" href="#SIOCGIFADDR"><code class="Dv">SIOCGIFADDR</code></a></dt>
<dd>Get interface address for protocol family.</dd>
<dt id="SIOCGIFDSTADDR"><a class="permalink" href="#SIOCGIFDSTADDR"><code class="Dv">SIOCGIFDSTADDR</code></a></dt>
<dd>Get point to point address for protocol family and interface.</dd>
<dt id="SIOCGIFBRDADDR"><a class="permalink" href="#SIOCGIFBRDADDR"><code class="Dv">SIOCGIFBRDADDR</code></a></dt>
<dd>Get broadcast address for protocol family and interface.</dd>
<dt id="SIOCSIFCAP"><a class="permalink" href="#SIOCSIFCAP"><code class="Dv">SIOCSIFCAP</code></a></dt>
<dd>Attempt to set the enabled capabilities field for the interface to the
value of the <var class="Va">ifr_reqcap</var> field of the
<var class="Vt">ifreq</var> structure. Note that, depending on the
particular interface features, some capabilities may appear hard-coded to
enabled, or toggling a capability may affect the status of other ones. The
supported capabilities field is read-only, and the
<var class="Va">ifr_curcap</var> field is unused by this call.</dd>
<dt id="SIOCGIFCAP"><a class="permalink" href="#SIOCGIFCAP"><code class="Dv">SIOCGIFCAP</code></a></dt>
<dd>Get the interface capabilities fields. The values for supported and
enabled capabilities will be returned in the
<var class="Va">ifr_reqcap</var> and <var class="Va">ifr_curcap</var>
fields of the <var class="Vt">ifreq</var> structure, respectively.</dd>
<dt id="SIOCGIFDESCR"><a class="permalink" href="#SIOCGIFDESCR"><code class="Dv">SIOCGIFDESCR</code></a></dt>
<dd>Get the interface description, returned in the
<var class="Va">buffer</var> field of <var class="Va">ifru_buffer</var>
struct. The user supplied buffer length should be defined in the
<var class="Va">length</var> field of <var class="Va">ifru_buffer</var>
struct passed in as parameter, and the length would include the
terminating nul character. If there is not enough space to hold the
interface length, no copy would be done and the
<var class="Va">buffer</var> field of <var class="Va">ifru_buffer</var>
would be set to NULL. The kernel will store the buffer length in the
<var class="Va">length</var> field upon return, regardless whether the
buffer itself is sufficient to hold the data.</dd>
<dt id="SIOCSIFDESCR"><a class="permalink" href="#SIOCSIFDESCR"><code class="Dv">SIOCSIFDESCR</code></a></dt>
<dd>Set the interface description to the value of the
<var class="Va">buffer</var> field of <var class="Va">ifru_buffer</var>
struct, with <var class="Va">length</var> field specifying its length
(counting the terminating nul).</dd>
<dt id="SIOCSIFFLAGS"><a class="permalink" href="#SIOCSIFFLAGS"><code class="Dv">SIOCSIFFLAGS</code></a></dt>
<dd>Set interface flags field. If the interface is marked down, any processes
currently routing packets through the interface are notified; some
interfaces may be reset so that incoming packets are no longer received.
When marked up again, the interface is reinitialized.</dd>
<dt id="SIOCGIFFLAGS"><a class="permalink" href="#SIOCGIFFLAGS"><code class="Dv">SIOCGIFFLAGS</code></a></dt>
<dd>Get interface flags.</dd>
<dt id="SIOCSIFMETRIC"><a class="permalink" href="#SIOCSIFMETRIC"><code class="Dv">SIOCSIFMETRIC</code></a></dt>
<dd>Set interface routing metric. The metric is used only by user-level
routers.</dd>
<dt id="SIOCGIFMETRIC"><a class="permalink" href="#SIOCGIFMETRIC"><code class="Dv">SIOCGIFMETRIC</code></a></dt>
<dd>Get interface metric.</dd>
<dt id="SIOCIFCREATE"><a class="permalink" href="#SIOCIFCREATE"><code class="Dv">SIOCIFCREATE</code></a></dt>
<dd>Attempt to create the specified interface. If the interface name is given
without a unit number the system will attempt to create a new interface
with an arbitrary unit number. On successful return the
<var class="Va">ifr_name</var> field will contain the new interface
name.</dd>
<dt id="SIOCIFDESTROY"><a class="permalink" href="#SIOCIFDESTROY"><code class="Dv">SIOCIFDESTROY</code></a></dt>
<dd>Attempt to destroy the specified interface.</dd>
</dl>
<p class="Pp">There are two requests that make use of a new structure:</p>
<dl class="Bl-tag">
<dt id="SIOCAIFADDR"><a class="permalink" href="#SIOCAIFADDR"><code class="Dv">SIOCAIFADDR</code></a></dt>
<dd>An interface may have more than one address associated with it in some
protocols. This request provides a means to add additional addresses (or
modify characteristics of the primary address if the default address for
the address family is specified). Rather than making separate calls to set
destination or broadcast addresses, or network masks (now an integral
feature of multiple protocols) a separate structure is used to specify all
three facets simultaneously (see below). One would use a slightly tailored
version of this struct specific to each family (replacing each sockaddr by
one of the family-specific type). Where the sockaddr itself is larger than
the default size, one needs to modify the
<a class="permalink" href="#ioctl~2"><code class="Fn" id="ioctl~2">ioctl</code></a>()
identifier itself to include the total size, as described in
<code class="Fn">ioctl</code>().</dd>
<dt id="SIOCDIFADDR"><a class="permalink" href="#SIOCDIFADDR"><code class="Dv">SIOCDIFADDR</code></a></dt>
<dd>This requests deletes the specified address from the list associated with
an interface. It also uses the <var class="Vt">ifaliasreq</var> structure
to allow for the possibility of protocols allowing multiple masks or
destination addresses, and also adopts the convention that specification
of the default address means to delete the first address for the interface
belonging to the address family in which the original socket was
opened.</dd>
<dt id="SIOCGIFALIAS"><a class="permalink" href="#SIOCGIFALIAS"><code class="Dv">SIOCGIFALIAS</code></a></dt>
<dd>This request provides means to get additional addresses together with
netmask and broadcast/destination from an interface. It also uses the
<var class="Vt">ifaliasreq</var> structure.</dd>
<dt id="SIOCGIFCONF"><a class="permalink" href="#SIOCGIFCONF"><code class="Dv">SIOCGIFCONF</code></a></dt>
<dd>Get interface configuration list. This request takes an
<var class="Vt">ifconf</var> structure (see below) as a value-result
parameter. The <var class="Va">ifc_len</var> field should be initially set
to the size of the buffer pointed to by <var class="Va">ifc_buf</var>. On
return it will contain the length, in bytes, of the configuration
list.</dd>
<dt id="SIOCIFGCLONERS"><a class="permalink" href="#SIOCIFGCLONERS"><code class="Dv">SIOCIFGCLONERS</code></a></dt>
<dd>Get list of clonable interfaces. This request takes an
<var class="Vt">if_clonereq</var> structure (see below) as a value-result
parameter. The <var class="Va">ifcr_count</var> field should be set to the
number of <code class="Dv">IFNAMSIZ</code> sized strings that can be fit
in the buffer pointed to by <var class="Va">ifcr_buffer</var>. On return,
<var class="Va">ifcr_total</var> will be set to the number of clonable
interfaces and the buffer pointed to by <var class="Va">ifcr_buffer</var>
will be filled with the names of clonable interfaces aligned on
<code class="Dv">IFNAMSIZ</code> boundaries.</dd>
</dl>
<div class="Bd Pp Li">
<pre>/*
* Structure used in SIOCAIFADDR request.
*/
struct ifaliasreq {
char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */
struct sockaddr ifra_addr;
struct sockaddr ifra_broadaddr;
struct sockaddr ifra_mask;
};</pre>
</div>
<div class="Bd Pp Li">
<pre>/*
* Structure used in SIOCGIFCONF request.
* Used to retrieve interface configuration
* for machine (useful for programs which
* must know all networks accessible).
*/
struct ifconf {
int ifc_len; /* size of associated buffer */
union {
caddr_t ifcu_buf;
struct ifreq *ifcu_req;
} ifc_ifcu;
#define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
#define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */
};</pre>
</div>
<div class="Bd Pp Li">
<pre>/* Structure used in SIOCIFGCLONERS request. */
struct if_clonereq {
int ifcr_total; /* total cloners (out) */
int ifcr_count; /* room for this many in user buffer */
char *ifcr_buffer; /* buffer for cloner names */
};</pre>
</div>
<div class="Bd Pp Li">
<pre>/* Structure used in SIOCGIFDESCR and SIOCSIFDESCR requests */
struct ifreq_buffer {
size_t length; /* length of the buffer */
void *buffer; /* pointer to userland space buffer */
};</pre>
</div>
</section>
<section class="Sh">
<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
ALSO</a></h1>
<p class="Pp"><a class="Xr">ioctl(2)</a>, <a class="Xr">socket(2)</a>,
<a class="Xr">intro(4)</a>, <a class="Xr">config(8)</a>,
<a class="Xr">routed(8)</a>, <a class="Xr">ifnet(9)</a></p>
</section>
<section class="Sh">
<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1>
<p class="Pp">The <code class="Nm">netintro</code> manual appeared in
<span class="Ux">4.3BSD-Tahoe</span>.</p>
</section>
</div>
<table class="foot">
<tr>
<td class="foot-date">October 14, 2020</td>
<td class="foot-os">FreeBSD 15.0</td>
</tr>
</table>
|
