.TH INTRO 4N "19 March 1982" .UC 4 .SH NAME net \- introduction to networking facilities .SH SYNOPSIS .B #include <sys/socket.h> .br .B #include <net/route.h> .SH DESCRIPTION .de _d .if t .ta .6i 2.1i 2.6i .\" 2.94 went to 2.6, 3.64 to 3.30 .if n .ta .84i 2.6i 3.30i .. .de _f .if t .ta .5i 1.25i 2.5i .\" 3.5i went to 3.8i .if n .ta .7i 1.75i 3.8i .. This section briefly describes the networking facilities available on the system. Documentation in this part of section 4 is broken up into three areas: .IR protocol-families , .IR protocols , and .IR "network interfaces" . Entries describing a protocol-family are marked ``4F'', protocol entries ``4P'', and network interfaces ``4V'' (for VAX specific devices) or ``4S'' (for Sun specific entries). .PP All network protocols are associated with a specific .IR 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 .IR 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. .PP A protocol supports one of the socket abstractions detailed in .IR 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. .PP 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 .IR config (8) program. The DIAGNOSTICS section lists messages which may appear on the console and in the system error log .I /usr/adm/messages due to errors in device operation. .SH 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. .SH ADDRESSING Associated with each protocol family is an address format. The following address formats are used by the system: .sp 1 .nf ._d #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 */ .fi .SH 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 outputing 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 .IR 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. .PP A routing table entry has the following form, as defined in .RI < net/route.h >; .sp 1 ._f .nf 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; }; .sp 1 .fi with .I rt_flags defined from, .sp 1 .nf ._d #define RTF_UP 0x1 /* route useable */ #define RTF_GATEWAY 0x2 /* destination is a gateway */ #define RTF_HOST 0x4 /* host entry (net otherwise) */ .fi .PP Routing table entries come in two flavors, for a specific host or for all hosts on a specific network. 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 receipient (i.e. the packet is forwarded). .PP 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 (the reference count field is non-zero), when it is deleted, the resources associated with it will not be reclaimed until further references to it are released. .PP The routing code may return EEXIST if requested to add an already existant entry, ESRCH if requested to delete an entry and it couldn't be found, or ENOBUFS if requested to add an entry and the system was low on resources. .PP There currently is no support for reading the routing tables; user processes are expected to read the kernel's memory through .IR /dev/kmem . .PP The use field is used by the routing code in providing a simple round-robin scheme of route selection when multiple routes to a destination are present; the heuristic is to choose the least used route. .SH SEE ALSO config(8), socket(2)