NETINTRO(4) OpenBSD Programmer's Manual NETINTRO(4)NAMEnetintro - introduction to networking facilities
SYNOPSIS
#include <sys/socket.h>
#include <net/route.h>
#include <net/if.h>
DESCRIPTION
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: protocol families (domains), protocols, and
network interfaces.
All network protocols are associated with a specific protocol family. 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 socket(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 socket(2).
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 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. 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 config(8)
program. The DIAGNOSTICS section lists messages which may appear on the
console and/or in the system error log, /var/log/messages (see
syslogd(8)), due to errors in device operation.
Network interfaces may be collected together into interface groups. An
interface group is a container that can be used generically when
referring to any interface related by some criteria. When an action is
performed on an interface group, such as packet filtering by the pf(4)
subsystem, the operation will be applied to each member interface in the
group, if supported by the subsystem. The ifconfig(8) utility can be
used to view and assign membership of an interface to an interface group
with the group modifier.
PROTOCOLS
The system currently supports the Internet protocols (IPv4 and IPv6),
Appletalk, and a few others. Raw socket interfaces are provided to the
IP protocol layer of the Internet. Consult the appropriate manual pages
in this section for more information regarding the support for each
protocol family.
ADDRESSING
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 a finer, more specific structure,
generally renaming the variant, which is discussed in the protocol family
manual page alluded to above.
struct sockaddr {
u_int8_t sa_len; /* total length */
sa_family_t sa_family; /* address family */
char sa_data[14]; /* actually longer */
};
The field sa_len contains the total length of the structure, which may
exceed 16 bytes. The following address values for sa_family are known to
the system (and additional formats are defined for possible future
implementation):
#define AF_LOCAL 1 /* local to host (pipes, portals) */
#define AF_INET 2 /* internetwork: UDP, TCP, etc. */
#define AF_HYLINK 15 /* NSC Hyperchannel */
#define AF_APPLETALK 16 /* AppleTalk */
#define AF_INET6 24 /* IPv6 */
#define AF_NATM 27 /* native ATM access */
#define AF_BLUETOOTH 32 /* Bluetooth */
The sa_data field contains the actual address value. Note that it may be
longer than 14 bytes.
ROUTING
OpenBSD provides some packet routing facilities. The kernel maintains a
routing information database, which is used in selecting the appropriate
network interface when transmitting 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 ioctl(2)'s used in earlier releases.
This facility is described in route(4).
INTERFACES
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, lo(4), do not.
The following ioctl(2) calls may be used to manipulate network
interfaces. The ioctl(2) is made on a socket (typically of type
SOCK_DGRAM) in the desired domain. Most of the requests take an ifreq
structure pointer as their parameter. This structure is as follows:
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;
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 /* p-to-p peer */
#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_mtu ifr_ifru.ifru_metric /* mtu (overload) */
#define ifr_media ifr_ifru.ifru_metric /* media options */
#define ifr_data ifr_ifru.ifru_data /* used by interface */
};
The supported ioctl(2) requests are:
SIOCSIFADDR struct ifreq *
Set the interface address for a protocol family. Following the
address assignment, the ``initialization'' routine for the
interface is called.
This call has been deprecated and superseded by the SIOCAIFADDR
call, described below.
SIOCSIFDSTADDR struct ifreq *
Set the point-to-point address for a protocol family and
interface.
This call has been deprecated and superseded by the SIOCAIFADDR
call, described below.
SIOCSIFBRDADDR struct ifreq *
Set the broadcast address for a protocol family and interface.
This call has been deprecated and superseded by the SIOCAIFADDR
call, described below.
SIOCGIFADDR struct ifreq *
Get the interface address for a protocol family.
SIOCGIFDSTADDR struct ifreq *
Get the point-to-point address for a protocol family and
interface.
SIOCGIFBRDADDR struct ifreq *
Get the broadcast address for a protocol family and interface.
SIOCGIFDESCR struct ifreq *
Get the interface description, returned in the ifru_data field.
SIOCSIFDESCR struct ifreq *
Set the interface description to the value of the ifru_data
field, limited to the size of IFDESCRSIZE.
SIOCSIFFLAGS struct ifreq *
Set the interface flags. 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 struct ifreq *
Get the interface flags.
SIOCSIFMEDIA struct ifreq *
Set the interface media settings. See ifmedia(4) for possible
values.
SIOCGIFMEDIA struct ifmediareq *
Get the interface media settings. The ifmediareq structure is as
follows:
struct ifmediareq {
char ifm_name[IFNAMSIZ]; /* if name, e.g. "en0" */
int ifm_current; /* current media options */
int ifm_mask; /* don't care mask */
int ifm_status; /* media status */
int ifm_active; /* active options */
int ifm_count; /* #entries in ifm_ulist array */
int *ifm_ulist; /* media words */
};
See ifmedia(4) for interpreting this value.
SIOCSIFMETRIC struct ifreq *
Set the interface routing metric. The metric is used only by
user-level routers.
SIOCGIFMETRIC struct ifreq *
Get the interface metric.
SIOCSIFPRIORITY struct ifreq *
Set the interface routing priority. The interface routing
priority influences the resulting routing priority of new static
routes added to the kernel using the specified interface. The
value is in the range of 0 to 16 with smaller numbers being
better.
SIOCGIFPRIORITY struct ifreq *
Get the interface priority.
SIOCAIFADDR struct ifaliasreq *
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, ifaliasreq, is used to specify
all three facets simultaneously (see below). One would use a
slightly tailored version of this structure specific to each
family (replacing each sockaddr by one of the family-specific
type). One should always set the length of a sockaddr, as
described in ioctl(2).
The ifaliasreq structure is as follows:
struct ifaliasreq {
char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */
struct sockaddr ifra_addr;
struct sockaddr ifra_dstaddr;
#define ifra_broadaddr ifra_dstaddr
struct sockaddr ifra_mask;
};
SIOCDIFADDR struct ifreq *
This request deletes the specified address from the list
associated with an interface. It also uses the ifaliasreq
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.
SIOCGIFCONF struct ifconf *
Get the interface configuration list. This request takes an
ifconf structure (see below) as a value-result parameter. The
ifc_len field should be initially set to the size of the buffer
pointed to by ifc_buf. On return it will contain the length, in
bytes, of the configuration list.
Alternately, if the ifc_len passed in is set to 0, SIOCGIFCONF
will set ifc_len to the size that ifc_buf needs to be to fit the
entire configuration list and will not fill in the other
parameters. This is useful for determining the exact size that
ifc_buf needs to be in advance. Note, however, that this is an
extension that not all operating systems support.
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 ret'd */
};
SIOCIFCREATE struct ifreq *
Attempt to create the specified interface.
SIOCIFDESTROY struct ifreq *
Attempt to destroy the specified interface.
SIOCIFGCLONERS struct if_clonereq *
Get the list of clonable interfaces. This request takes an
if_clonereq structure pointer (see below) as a value-result
parameter. The ifcr_count field should be set to the number of
IFNAMSIZ-sized strings that can fit in the buffer pointed to by
ifcr_buffer. On return, ifcr_total will be set to the number of
clonable interfaces, and the buffer pointed to by ifcr_buffer
will be filled with the names of clonable interfaces aligned on
IFNAMSIZ boundaries.
The if_clonereq structure is as follows:
struct if_clonereq {
int ifcr_total; /* total cloners (out) */
int ifcr_count; /* room for this many in user buf */
char *ifcr_buffer; /* buffer for cloner names */
};
SIOCAIFGROUP struct ifgroupreq *
Associate the interface named by ifgr_name with the interface
group named by ifgr_group. The ifgroupreq structure is as
follows:
struct ifg_req {
char ifgrq_group[IFNAMSIZ];
};
struct ifgroupreq {
char ifgr_name[IFNAMSIZ];
u_int ifgr_len;
union {
char ifgru_group[IFNAMSIZ];
struct ifg_req *ifgru_groups;
} ifgr_ifgru;
#define ifgr_group ifgr_ifgru.ifgru_group
#define ifgr_groups ifgr_ifgru.ifgru_groups
};
SIOCGIFGROUP struct ifgroupreq *
Retrieve the list of groups for which an interface is a member.
The interface is named by ifgr_name. On enter, the amount of
memory in which the group names will be written is stored in
ifgr_len, and the group names themselves will be written to the
memory pointed to by ifgr_groups. On return, the amount of
memory actually written is returned in ifgr_len.
Alternately, if the ifgr_len passed in is set to 0, SIOCGIFGROUP
will set ifgr_len to the size that ifgr_groups needs to be to fit
the entire group list and will not fill in the other parameters.
This is useful for determining the exact size that ifgr_groups
needs to be in advance.
SIOCDIFGROUP struct ifgroupreq *
Remove the membership of the interface named by ifgr_name from
the group ifgr_group.
SEE ALSOnetstat(1), ioctl(2), socket(2), inet(3), arp(4), bluetooth(4),
bridge(4), ifmedia(4), inet(4), intro(4), ip(4), ip6(4), lo(4), pf(4),
tcp(4), udp(4), hosts(5), networks(5), bgpd(8), config(8), ifconfig(8),
mrouted(8), netstart(8), ospfd(8), ripd(8), route(8)HISTORY
The netintro manual appeared in 4.3BSD-Tahoe.
OpenBSD 4.9 January 29, 2009 OpenBSD 4.9