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researchv10 Dan Cross

.TH IP 4
.CT 2 comm_mach
.SH NAME
ip, ip_ld \- DARPA internet protocol
.SH SYNOPSIS
.B #include <sys/inio.h>
.br
.B #include <sys/inet/in.h>
.br
.B #include <sys/inet/ip_var.h>
.SH DESCRIPTION
.PP
The
.I ip_ld
line discipline and the
.F /dev/ip*
files together implement the DARPA IP datagram protocol.
They are used by
the programs described in
.IR ipconfig (8)
and
.IR route (8).
.PP
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
.I ip_ld
and setting local and remote addresses
with
.I ioctl
calls.
Thereafter,
data received from the network
are assumed to be IP packets,
and are intercepted by the line discipline.
Packets destined for the local address of an active IP interface
are routed for reading on one of the
.I ip
device files.
Other packets are routed to the IP interface
with a matching remote address
and retransmitted.
.PP
Data written on
.I 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.
.PP
A packet consists of a single stream record,
followed by a delimiter:
at most one packet is returned by a
.I read
call;
an entire packet must be presented in a single
.IR write .
A packet includes the IP header.
Numbers in the header are in host byte order.
.PP
Different
.I 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
.I ip
device is open,
it may not be opened again.
IP packets are often processed by pushing a line discipline
such as
.IR tcp_ld
on an
.I ip
device,
rather than by explicit
.I read
and
.I write
calls;
see
.IR tcp (4).
.PP
The following
.IR ioctl (2)
calls, defined in
.BR <sys/inio.h> ,
apply to an IP interface.
.B IPIOLOCAL
and either
.B IPIOHOST
or
.B IPIONET
must be called on each interface
before packets will be routed correctly.
Type
.BR in_addr ,
defined in
.BR <sys/inet/in.h> ,
is a 32-bit integer
representing an IP address
in host byte order.
.nr Pw \w'\f5IPIORESOLVE 'u
.TP \n(Pwu
.B IPIOLOCAL
The third argument points to an
.BR in_addr :
the local IP address for this interface.
.TP
.B IPIOHOST
The third argument points to an
.BR in_addr :
the remote IP address of the single host
reachable through this interface.
.TP
.B IPIONET
The third argument
points to an
.BR 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
.BI ( address & mask )== net-address
is part of the network.
The default mask depends on
the IP address class;
see the IP protocol standard for details.
.TP
.B IPIOMASK
The third argument points to an
.B in_addr
containing a new network mask for this interface.
.TP
.B 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.
.TP
.B IPIOARP
The network device for this interface
is an Ethernet.
Discard the Ethernet header from each incoming packet.
When sending a packet,
prefix an Ethernet header
containing protocol type
.B 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
.B in_addr
containing the offending address
available for reading
on this file descriptor
(the one on which
.I ip_ld
was pushed).
.TP
.B IPIORESOLVE
The third argument points to a structure:
.EX
struct {
	in_addr inaddr;
	unsigned char enaddr[6];
};
.EE
Add an entry to the table consulted after
.BR IPIOARP ,
mapping IP address
.B inaddr
to Ethernet address
.BR enaddr .
.LP
The following
.I ioctl
calls, define in
.BR <sys/inio.h> ,
apply to the entire IP subsystem;
they may be used on any file with
.I ip_ld
pushed.
.TP \n(Pwu
.B IPIOROUTE
The third argument points to a structure:
.EX
struct route {
	in_addr dst;
	in_addr gate;
};
.EE
Arrange that henceforth,
any IP packet destined for address
.B dst
will be routed as if destined for
.BR gate .
.TP
.B IPIOGETIFS
The third argument points to a union as follows.
The structure is defined in
.BR <sys/inet/ip_var.h> .
.EX
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;
};
.EE
Before the call,
.B index
should contain an integer
naming an entry in the system's table
of active interfaces.
Interfaces are numbered in a continuous sequence starting at 0.
Out-of-range numbers return an error.
After the call,
.B ipif
is filled in with various numbers
about that interface.
.SH FILES
.B /dev/ip*
.SH SEE ALSO
.IR ioctl (2),
.IR internet (3),
.IR ipconfig (8),
.IR route (8)
.br
DARPA standards RFC 791, RFC 1122
.SH BUGS
The ARP mechanism should be generalized
to deal with networks other than Ethernet.
There is only one ARP table for the entire system;
there should be one for each interface.
.br
The structures used by
.B IPIOROUTE
and
.B IPIORESOLVE
should appear in a header file somewhere.

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