INTRO(4N) Domain/OS BSD INTRO(4N)
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 4 is broken up into three
areas: protocol families (domains), protocols, and network interfaces.
Entries describing a protocol family are marked "4F," while entries
describing protocol use are marked "4P." Hardware support for network
interfaces are found among the standard "4" 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 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, /usr/adm/messages, due to errors
in device operation.
PROTOCOLS
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 IMP link layer (1822). 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 (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_PUP 4 /* pup protocols: for example BSP */
#define AF_HYLINK 15 /* NSC Hyperchannel */
ROUTING
The network facilities provide 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 database 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) */
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.
Otherwise, the interface is requested to address the packet to the
gateway listed in the routing entry (that is 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 nonzero), 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. 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.
Domain/OS EXTENSION
BSD TCP/IP gets routing information by seeking into /dev/kmem. The
Domain/OS version of TCP/IP does not locate its TCP/IP information in
/dev/kmem. Rather, it provides ioctl routines that return copies of
internal data structures. The SIOCGRTTAB returns a copy of the internal
routing table. The SIOCGRTTAB routine, which is declared in the file
<sys/ioctl.h>, returns the data structures, rt_kentry, rt_ktab. The data
structures are defined in the file: <net/route.h>.
The SIOCGRTTAB routine dumps a copy of an entire, dynamically-sized
internal table. Since the caller cannot know the size of the table in
advance of making the ioctl request, an extra field in the request
structure, the "max" field, has been added to the standard "length" and
"buffer" fields used in ifconf and ifreq. (See below.)
To use this ioctl routine, the caller sets the "length" field to the size
of the included buffer area, but the TCP daemon sets the "max" field when
returning the request structure. The value of "max" is the number of
bytes needed to return a copy of the entire requested table. The caller
can determine if the entire table was returned by checking that the value
of "length" is greater than or equal to the value of "max". If it is,
the entire table has been returned. For efficiency, make two requests.
First, use a structure with the length set to zero; when the TCP daemon
returns the structure, the "max" field will contain the size in bytes of
the buffer needed to store a copy of the entire table. Then, make a
second call specifying the buffer of the exact size. (While it's
possible that the table make have shrunk or grown between the two
requests, in most cases, the second buffer will be close to the correct
size.)
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 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 {
char ifr_name[16]; /* name of interface (for example "ec0") */
union {
struct sockaddr ifru_addr;
struct sockaddr ifru_dstaddr;
struct sockaddr ifru_broadaddr;
short ifru_flags;
int ifru_metric;
} 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 /* routing metric */
};
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.
/*
* 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 */
};
Domain/OS EXTENSION
SIOCGIFENT
Get a single entry in the interface control block table. Use
SIOCGIFENT to get the name of all the configured interfaces, and
then use any of the names to request a copy of the associated
control block. Returns copies of the data structures, if_kentry,
and if_ktab, which are defined in <net/if.h>. Use SIOCGIFENT as you
would use SIOCGIFMETIC or SIOCGIFDSTADDR. Make a > SIOCGIFENT call
to get the name of all the configured interfaces, and then use any
of these names to request a copy of the associated control block.
SEE ALSO
socket(2), ioctl(2), intro(4), routed(8C)