intro(5N) intro(5N)
NAME
networking - introduction to networking facilities
SYNOPSIS
#include <sys/socket.h>
#include <net/route.h>
#include <net/if.h>
DESCRIPTION
This section briefly describes the networking facilities
available in the system. Documentation in this part of
Section 5 is broken up into three areas: protocol-families,
protocols, and network interfaces. Entries describing a
protocol-family are marked ``5F'', while entries describing
protocol use are marked ``5P''. Hardware support for
network interfaces are found among the standard Section 5
entries.
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(2N) 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(2N). 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 SOCKSTREAM 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.
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PROTOCOLS
The system currently supports only the DARPA Internet
protocols fully. Raw socket interfaces are provided to IP
protocol layer of the DARPA Internet, to the IMP link layer
(1822), and to Xerox PUP-1 layer operating on top of 3Mb/s
Ethernet interfaces. 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.
The following address formats are used by the system:
#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_PUP 4 /*pup protocols: e.g. BSP*/
ROUTING
The network facilities provided limited packet routing. A
simple set of data structures comprise a ``routing table''
used in selecting the appropriate network interface when
transmitting packets. This table contains a single entry
for each route to a specific network or host. A user
process, the routing daemon, maintains this data base with
the aid of two socket specific ioctl(2) commands, SIOCADDRT
and SIOCDELRT. The commands allow the addition and deletion
of a single routing table entry, respectively. Routing
table manipulations may only be carried out by super-user.
A routing table entry has the following form, as defined in
<net/route.h>;
struct rtentry {
u_long rt_hash;
struct sockaddr rt_dst;
struct sockaddr rt_gateway;
short rt_flags;
short rt_refcnt;
u_long rt_use;
struct ifnet *rt_ifp;
};
with rtflags defined from,
#define RTF_UP 0x1 /*route usable*/
#define RTF_GATEWAY 0x2 /*destination is a gateway*/
#define RTF_HOST 0x4 /*host entry (net otherwise)*/
Routing table entries come in three flavors: for a specific
host, for all hosts on a specific network, for any
destination not matched by entries of the first two types (a
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wildcard route). When the system is booted, each network
interface autoconfigured installs a routing table entry when
it wishes to have packets sent through it. Normally the
interface specifies the route through it is a ``direct''
connection to the destination host or network. If the route
is direct, the transport layer of a protocol family usually
requests the packet be sent to the same host specified in
the packet. Otherwise, the interface may be requested to
address the packet to an entity different from the eventual
recipient (i.e. the packet is forwarded).
Routing table entries installed by a user process may not
specify the hash, reference count, use, or interface fields;
these are filled in by the routing routines. If a route is
in use when it is deleted (rtrefcnt is non-zero), the
resources associated with it will not be reclaimed until
further references to it are released.
The routing code returns EEXIST if requested to duplicate an
existing entry, ESRCH if requested to delete a non-existant
entry, or ENOBUFS if insufficient resources were available
to install a new route.
User processes read the routing tables through the /dev/kmem
device.
The rtuse field contains the number of packets sent along
the route. This value is used to select among multiple
routes to the same destination. When multiple routes to the
same destination exist, the least used route is selected.
A wildcard routing entry is specified with a zero
destination address value. Wildcard routes are used only
when the system fails to find a route to the destination
host and network. The combination of wildcard routes and
routing redirects can provide an economical mechanism for
routing traffic.
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(5), do not.
At boot time each interface which has underlying hardware
support makes itself known to the system during the
autoconfiguration process. Once the interface has acquired
its address it is expected to install a routing table entry
so that messages may be routed through it. Most interfaces
require some part of their address specified with an
SIOCSIFADDR ioctl before they will allow traffic to flow
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through them. On interfaces where the network-link layer
address mapping is static, only the network number is taken
from the ioctl; the remainder is found in a hardware
specific manner. On interfaces which provide dynamic
network-link layer address mapping facilities (e.g. 10Mb/s
Ethernets), the entire address specified in the ioctl is
used.
The following ioctl calls may be used to manipulate network
interfaces. Unless specified otherwise, the request takes
an ifrequest structure as its parameter. This structure has
the form
struct ifreq {
char ifr_name[16]; /* name of interface
(e.g. "ec0") */
union {
struct sockaddr ifru_addr;
struct sockaddr ifru_dstaddr;
short ifru_flags;
} 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_flags ifr_ifru.ifru_flags /* flags */
};
SIOCSIFADDR
Set interface address. Following the address
assignment, the ``initialization'' routine for the
interface is called.
SIOCGIFADDR
Get interface address.
SIOCSIFDSTADDR
Set point to point address for
SIOCGIFDSTADDR
Get point to point address for interface.
SIOCSIFFLAGS
Set interface flags field. If the interface is marked
down, any processes currently routing packets through
the interface are notified.
SIOCGIFFLAGS
Get interface flags.
SIOCGIFCONF
Get interface configuration list. This request takes
an ifconf structure (see below) as a value-result
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parameter. The ifclen field should be initially set
to the size of the buffer pointed to by ifcbuf. On
return it will contain the length, in bytes, of the
configuration list.
/*
* .B 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 */
};
socket(2N), ioctl(2), routed(1M).
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