4.3BSD-Reno/share/man/cat4/networking.0
NETINTRO(4) 1990 NETINTRO(4)
NNAAMMEE
networking - introduction to networking facilities
SSYYNNOOPPSSIISS
##iinncclluuddee <<ssyyss//ssoocckkeett..hh>>
##iinncclluuddee <<nneett//rroouuttee..hh>>
##iinncclluuddee <<nneett//iiff..hh>>
DDEESSCCRRIIPPTTIIOONN
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: _p_r_o_t_o_c_o_l
_f_a_m_i_l_i_e_s (domains), _p_r_o_t_o_c_o_l_s, and _n_e_t_w_o_r_k _i_n_t_e_r_f_a_c_e_s.
All network protocols are associated with a specific _p_r_o_t_o_-
_c_o_l _f_a_m_i_l_y. 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 implemen-
tations do not. A protocol family is normally comprised of
a number of protocols, one per _s_o_c_k_e_t(2) 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.
A protocol supports one of the socket abstractions detailed
in _s_o_c_k_e_t(2). A specific protocol may be accessed either by
creating a socket of the appropriate type and protocol fam-
ily, or by requesting the protocol explicitly when creating
a socket. Protocols normally accept only one type of
address format, usually determined by the addressing struc-
ture 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 SOCK_STREAM abstraction may allow
more than one byte of out-of-band data to be transmitted per
out-of-band message.
A network interface is similar to a device interface. Net-
work 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 net-
work interface entry gives a sample specification of the
related drivers for use in providing a system description to
the _c_o_n_f_i_g(8) program. The DIAGNOSTICS section lists mes-
sages which may appear on the console and/or in the system
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NETINTRO(4) 1990 NETINTRO(4)
error log, /_v_a_r/_l_o_g/_m_e_s_s_a_g_e_s (see _s_y_s_l_o_g_d(8)), due to errors
in device operation.
PPRROOTTOOCCOOLLSS
The system currently supports the DARPA 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 DARPA Internet, to the IMP link layer
(1822), and to the IDP protocol of Xerox NS. Consult the
appropriate manual pages in this section for more informa-
tion regarding the support for each protocol family.
AADDDDRREESSSSIINNGG
Associated with each protocol family is an address format.
All network address 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.
struct sockaddr {
u_char sa_len;
u_char sa_family;
char sa_data[14];
};
The field sa_len contains the total length of the of the
structure, which may exceed 16 bytes. The following address
values for _s_a__f_a_m_i_l_y are known to the system (and additional
formats are defined for possible future implementation):
#define AF_UNIX 1 /* local to host (pipes, portals) */
#define AF_INET 2 /* internetwork: UDP, TCP, etc. */
#define AF_IMPLINK 3 /* arpanet imp addresses */
#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 */
RROOUUTTIINNGG
provides some packet routing facilities. The kernel main-
tains a routing information database, which is used in
selecting the appropriate network interface when transmit-
ting packets.
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 _i_o_c_t_l's used in
earlier releases.
This facility is described in _r_o_u_t_e(4).
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NETINTRO(4) 1990 NETINTRO(4)
IINNTTEERRFFAACCEESS
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,
_l_o(4), do not.
The following _i_o_c_t_l calls may be used to manipulate network
interfaces. The _i_o_c_t_l is made on a socket (typically of
type SOCK_DGRAM) in the desired domain. Most of the
requests supported in earlier releases take an _i_f_r_e_q struc-
ture as its parameter. This structure has the form
struct ifreq {
#define IFNAMSIZ 16
char ifr_name[IFNAMSIZE]; /* if name, e.g. "en0" */
union {
struct sockaddr ifru_addr;
struct sockaddr ifru_dstaddr;
struct sockaddr ifru_broadaddr;
short ifru_flags;
int ifru_metric;
caddr_t ifru_data;
} 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_flags ifr_ifru.ifru_flags /* flags */
#define ifr_metric ifr_ifru.ifru_metric /* metric */
#define ifr_data ifr_ifru.ifru_data /* for use by interface */
};
Calls which are now depricated are:
SIOCSIFADDR
Set interface address for protocol family. Following
the address assignment, the ``initialization'' routine
for the interface is called.
SIOCSIFDSTADDR
Set point to point address for protocol family and
interface.
SIOCSIFBRDADDR
Set broadcast address for protocol family and inter-
face.
_I_o_c_t_l_s requests to obtain addresses and requests both to set
and retreive other data are still fully supported and use
the _i_f_r_e_q structure:
SIOCGIFADDR
Get interface address for protocol family.
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NETINTRO(4) 1990 NETINTRO(4)
SIOCGIFDSTADDR
Get point to point address for protocol family and
interface.
SIOCGIFBRDADDR
Get broadcast address for protocol family and inter-
face.
SIOCSIFFLAGS
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.
SIOCGIFFLAGS
Get interface flags.
SIOCSIFMETRIC
Set interface routing metric. The metric is used only
by user-level routers.
SIOCGIFMETRIC
Get interface metric.
There are two requests that make use of a new structure:
SIOCAIFADDR
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 charac-
teristics of the primary address if the default address
for the address family is specified). Rather than mak-
ing 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:
struct ifaliasreq {
char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */
struct sockaddr ifra_addr;
struct sockaddr ifra_broadaddr;
struct sockaddr ifra_mask;
};
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 _i_o_c_t_l identifier itself to include
the total size, as described in _i_o_c_t_l(2).
SIOCDIFADDR
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NETINTRO(4) 1990 NETINTRO(4)
This requests deletes the specified address from the
list associated with an interface. It also uses the
if_aliasreq structure to allow for the possibility of
protocols allowing multiple masks or destination
addresses, and also adopts the convention that specifi-
cation of the default address means to delete the first
address for the interface belonging to the address fam-
ily in which the original socket was opened.
SIOCGIFCONF
Get interface configuration list. This request takes
an _i_f_c_o_n_f structure (see below) as a value-result
parameter. The _i_f_c__l_e_n field should be initially set
to the size of the buffer pointed to by _i_f_c__b_u_f. On
return it will contain the length, in bytes, of the
configuration list.
/*
* 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 */
};
SSEEEE AALLSSOO
socket(2), ioctl(2), intro(4), config(8), routed(8C)
Printed 7/27/90 June 5