IP(4) IP(4)
NAME
ip, ip_ld - DARPA internet protocol
SYNOPSIS
#include <sys/inio.h>
#include <sys/inet/in.h>
#include <sys/inet/ip_var.h>
DESCRIPTION
The ip_ld line discipline and the files together implement
the DARPA IP datagram protocol. They are used by the pro-
grams described in ipconfig(8) and route(8).
Each Ethernet device, Datakit channel, or other stream that
is to send and receive IP packets must be registered as an
`IP interface' by pushing ip_ld and setting local and remote
addresses with ioctl calls. Thereafter, data received from
the network are assumed to be IP packets, and are inter-
cepted by the line discipline. Packets destined for the
local address of an active IP interface are routed for read-
ing on one of the ip device files. Other packets are routed
to the IP interface with a matching remote address and
retransmitted.
Data written on ip devices are taken to be IP packets, are
handed to the IP interface with a matching address, and are
sent. Packets destined for unreachable places are quietly
dropped.
A packet consists of a single stream record, followed by a
delimiter: at most one packet is returned by a read call; an
entire packet must be presented in a single write. A packet
includes the IP header. Numbers in the header are in host
byte order.
Different ip devices handle different protocols atop IP.
The minor device is the protocol number in the IP header;
e.g. 6 for TCP or 17 for UDP. While an ip device is open,
it may not be opened again. IP packets are often processed
by pushing a line discipline such as tcp_ld on an ip device,
rather than by explicit read and write calls; see tcp(4).
The following ioctl(2) calls, defined in <sys/inio.h>, apply
to an IP interface. IPIOLOCAL and either IPIOHOST or
IPIONET must be called on each interface before packets will
be routed correctly. Type in_addr, defined in
<sys/inet/in.h>, is a 32-bit integer representing an IP
address in host byte order.
IPIOLOCAL The third argument points to an in_addr: the
IP(4) IP(4)
local IP address for this interface.
IPIOHOST The third argument points to an in_addr: the
remote IP address of the single host reachable
through this interface.
IPIONET The third argument points to an in_addr: the
remote IP address of the network of many hosts
reachable through this interface. IP addresses
are matched to the network address by applying
an internal bit-mask: any IP address for which
(address&mask)==net-address is part of the net-
work. The default mask depends on the IP
address class; see the IP protocol standard for
details.
IPIOMASK The third argument points to an in_addr contain-
ing a new network mask for this interface.
IPIOMTU The third argument points to an integer number
of bytes. IP packets larger than this size
(1500 by default) will be split into smaller
ones before being sent through this interface.
IPIOARP The network device for this interface is an Eth-
ernet. Discard the Ethernet header from each
incoming packet. When sending a packet, prefix
an Ethernet header containing protocol type 0x8
and a destination address obtained by looking up
the IP destination address in a table. If the
IP address is not in the table, discard the
packet, and make an in_addr containing the
offending address available for reading on this
file descriptor (the one on which ip_ld was
pushed).
IPIORESOLVE The third argument points to a structure:
struct {
in_addr inaddr;
unsigned char enaddr[6];
};
Add an entry to the table consulted after
IPIOARP, mapping IP address inaddr to Ethernet
address enaddr.
The following ioctl calls, define in <sys/inio.h>, apply to
the entire IP subsystem; they may be used on any file with
ip_ld pushed.
IPIOROUTE The third argument points to a structure:
struct route {
in_addr dst;
IP(4) IP(4)
in_addr gate;
};
Arrange that henceforth, any IP packet destined
for address dst will be routed as if destined
for gate.
IPIOGETIFS The third argument points to a union as follows.
The structure is defined in <sys/inet/ip_var.h>.
union {
int index;
struct ipif {
struct queue *queue;
int flags;
int mtu;
in_addr thishost;
in_addr that;
in_addr mask;
in_addr broadcast;
int ipackets, ierrors;
int opackets, oerrors;
int arp;
int dev;
} ipif;
};
Before the call, index should contain an integer
naming an entry in the system's table of active
interfaces. Interfaces are numbered in a con-
tinuous sequence starting at 0. Out-of-range
numbers return an error. After the call, ipif
is filled in with various numbers about that
interface.
FILES
/dev/ip*
SEE ALSO
ioctl(2), internet(3), ipconfig(8), route(8)
DARPA standards RFC 791, RFC 1122
BUGS
The ARP mechanism should be generalized to deal with net-
works other than Ethernet. There is only one ARP table for
the entire system; there should be one for each interface.
The structures used by IPIOROUTE and IPIORESOLVE should
appear in a header file somewhere.