NETINTRO(7) NETINTRO(7)
networking - introduction to networking facilities
#include <sys/socket.h>
#include <net/route.h>
#include <net/if.h>
This section briefly describes the networking facilities available in the
system. Documentation in this part of section 7 is broken up into three
areas: protocol families (domains), protocols, and network interfaces.
Entries describing a protocol family are marked ``7F,'' while entries
describing protocol use are marked ``7P.'' Hardware support for network
interfaces are found among the standard ``7'' 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(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 ethernet(7) manual entry
lists messages which may appear on the console and/or in the system error
log, /var/adm/SYSLOG (see syslogd(1M)), due to errors in device
operation.
The system currently supports the DARPA Internet protocols. Raw socket
interfaces are provided to the IP protocol layer of the DARPA Internet
and to the link-level layer. Consult the appropriate manual pages in
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this section for more information regarding the support for each protocol
family.
Associated with each protocol family is an address format. The following
address formats are used by the system (and additional formats are
defined for possible future implementation):
#define AF_UNIX 1 /* local to host (pipes) */
#define AF_INET 2 /* internetwork: UDP, TCP, etc. */
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 rt_flags defined from,
#define RTF_UP 0x1 /* route usable */
#define RTF_GATEWAY 0x2 /* destination is a gateway */
#define RTF_HOST 0x4 /* host entry (net otherwise) */
#define RTF_DYNAMIC 0x10 /* created dynamically (by redirect) */
#define RTF_MODIFIED 0x10 /* modified dynamically (by redirect) */
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 wildcard route). When the system is booted and
addresses are assigned to the network interfaces, each protocol family
installs a routing table entry for each interface when it is ready for
traffic. Normally the protocol specifies the route through each
interface as 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.
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Otherwise, the interface is requested to address the packet to the
gateway listed in the routing entry (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 (rt_refcnt
is non-zero), the routing entry will be marked down and removed from the
routing table, but the resources associated with it will not be reclaimed
until all references to it are released. The routing code returns EEXIST
if requested to duplicate an existing entry, ESRCH if requested to delete
a non-existent 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 rt_use field contains the number of packets
sent along the route.
When routing a packet, the kernel will first attempt to find a route to
the destination host. Failing that, a search is made for a route to the
network of the destination. Finally, any route to a default
(``wildcard'') gateway is chosen. If multiple routes are present in the
table, the first route found will be used. If no entry is found, the
destination is declared to be unreachable.
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.
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(7), do not.
The following ioctl calls may be used to manipulate network interfaces.
The ioctl is made on a socket (typically of type SOCK_DGRAM) in the
desired domain. Unless specified otherwise, the request takes an
ifrequest structure as its parameter. This structure has the form
struct ifreq {
#define IFNAMSIZ 16
char ifr_name[IFNAMSIZE]; /* if name, e.g. "enp0" */
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 */
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#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 */
};
SIOCSIFADDR
Set interface address for protocol family. Following the address
assignment, the ``initialization'' routine for the interface is
called.
SIOCGIFADDR
Get interface address for protocol family.
SIOCSIFDSTADDR
Set point to point address for protocol family and interface.
SIOCGIFDSTADDR
Get point to point address for protocol family and interface.
SIOCSIFBRDADDR
Set broadcast address for protocol family and interface.
SIOCGIFBRDADDR
Get broadcast address for protocol family and interface.
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.
SIOCGIFCONF
Get 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.
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/*
* 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(2), ioctl(2), routed(1M), route(7F), IRIX Network Programming
Guide.
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