INTRO(4N) COMMAND REFERENCE INTRO(4N) NAME intro - 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 describes three network-related areas: protocol- families, 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 netconfig(8n) program. The DIAGNOSTICS section lists messages which may appear on the console and Printed 4/6/89 1
INTRO(4N) COMMAND REFERENCE INTRO(4N) in the system error log /usr/adm/messages due to errors in device operation. Protocols The system currently supports only the DARPA Internet protocols fully. Raw socket interfaces are provided to the IP protocol layer of the DARPA 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. The following address formats are used by the system: #define AF_UNIX 1 /* local to host (pipes, streams) */ #define AF_INET 2 /* internetwork: UDP, TCP, etc. */ 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 superuser. 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) */ Printed 4/6/89 2
INTRO(4N) COMMAND REFERENCE INTRO(4N) 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, each network interface autoconfigured installs a routing table entry when it wishes to have packets sent through it. Normally the interface specifies that 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 (rt_refcnt 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-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. 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(4n), 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 Printed 4/6/89 3
INTRO(4N) COMMAND REFERENCE INTRO(4N) 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 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. "lan0") */ union { struct sockaddr ifru_addr; struct sockaddr ifru_dstaddr; short ifru_flags; caddr_t ifru_data; u_short ifru_tdr; u_char ifru_eaddr[6]; } 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 */ #define ifr_data ifr_ifru.ifru_data /* data */ #define ifr_tdr ifr_ifru.ifru_tdr /* tdr result */ #define ifr_eaddr ifr_ifru.ifru_eaddr /* IEEE 802.3 address */ }; SIOCSIFADDR Set interface address. If the family is AF_INET then the Internet address is set; family AF_UNSPEC sets the hardware address (Ethernet). Following the address assignment, the ``initialization'' routine for the interface is called. SIOCGIFADDR Get interface address. SIOCSIFDSTADDR Set point to point address for interface. 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. Printed 4/6/89 4
INTRO(4N) COMMAND REFERENCE INTRO(4N) SIOCGIFFLAGS Get interface flags. 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 */ }; SEE ALSO socket(2), ioctl(2), netconfig(8n), lan(4n), and routed(8n). Printed 4/6/89 5
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