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BSD mandoc
NAME
inet
- Internet protocol family
SYNOPSIS
#include <sys/types.h>
#include <netinet/in.h>
DESCRIPTION
The Internet protocol family is a collection of protocols
layered atop the
Internet Protocol
(IP
)
transport layer, and utilizing the Internet address format.
The Internet family provides protocol support for the
SOCK_STREAM , SOCK_DGRAM
and
SOCK_RAW
socket types; the
SOCK_RAW
interface provides access to the
IP
protocol.
ADDRESSING
Internet addresses are four byte quantities, stored in
network standard format (on little endian machines, such as the
alphaamd64i386
and
ia64
these are word and byte reversed).
The include file
#include <netinet/in.h>
defines this address
as a discriminated union.
Sockets bound to the Internet protocol family utilize
the following addressing structure,
Sockets may be created with the local address
INADDR_ANY
to affect
``wildcard''
matching on incoming messages.
The address in a
connect(2)
or
sendto(2)
call may be given as
INADDR_ANY
to mean
``this host''
The distinguished address
INADDR_BROADCAST
is allowed as a shorthand for the broadcast address on the primary
network if the first network configured supports broadcast.
PROTOCOLS
The Internet protocol family is comprised of
the
IP
network protocol, Internet Control
Message Protocol
(ICMP
)
Internet Group Management Protocol
(IGMP
)
Transmission Control
Protocol
(TCP
)
and User Datagram Protocol
(UDP
)
TCP
is used to support the
SOCK_STREAM
abstraction while
UDP
is used to support the
SOCK_DGRAM
abstraction.
A raw interface to
IP
is available
by creating an Internet socket of type
SOCK_RAW
The
ICMP
message protocol is accessible from a raw socket.
The 32-bit Internet address contains both network and host parts.
However, direct examination of addresses is discouraged.
For those
programs which absolutely need to break addresses into their component
parts, the following
ioctl(2)
commands are provided for a datagram socket in the Internet domain;
they have the same form as the
SIOCIFADDR
command (see
intro(4)).
SIOCSIFNETMASK
Set interface network mask.
The network mask defines the network part of the address;
if it contains more of the address than the address type would indicate,
then subnets are in use.
SIOCGIFNETMASK
Get interface network mask.
MIB Variables
A number of variables are implemented in the net.inet branch of the
sysctl(3)
MIB.
In addition to the variables supported by the transport protocols
(for which the respective manual pages may be consulted),
the following general variables are defined:
IPCTL_FORWARDING
(ip.forwarding)
Boolean: enable/disable forwarding of IP packets.
Defaults to off.
IPCTL_FASTFORWARDING
(ip.fastforwarding)
Boolean: enable/disable the use of
fast IP forwarding
code.
Defaults to off.
When
fast IP forwarding
is enabled, IP packets are forwarded directly to the appropriate network
interface with direct processing to completion, which greatly improves
the throughput.
All packets for local IP addresses, non-unicast, or with IP options are
handled by the normal IP input processing path.
All features of the normal (slow) IP forwarding path are supported
including firewall (through
pfil(9)
hooks) checking, except
ipsec(4)
tunnel brokering.
The
IP fastforwarding
path does not generate ICMP redirect or source quench messages.
IPCTL_SENDREDIRECTS
(ip.redirect)
Boolean: enable/disable sending of ICMP redirects in response to
IP
packets for which a better, and for the sender directly reachable, route
and next hop is known.
Defaults to on.
IPCTL_DEFTTL
(ip.ttl)
Integer: default time-to-live
(``TTL''
)
to use for outgoing
IP
packets.
IPCTL_ACCEPTSOURCEROUTE
(ip.accept_sourceroute)
Boolean: enable/disable accepting of source-routed IP packets (default false).
IPCTL_SOURCEROUTE
(ip.sourceroute)
Boolean: enable/disable forwarding of source-routed IP packets (default false).
IPCTL_RTEXPIRE
(ip.rtexpire)
Integer: lifetime in seconds of protocol-cloned
IP
routes after the last reference drops (default one hour).
This value varies dynamically as described above.
IPCTL_RTMINEXPIRE
(ip.rtminexpire)
Integer: minimum value of ip.rtexpire (default ten seconds).
This value has no effect on user modifications, but restricts the dynamic
adaptation described above.
IPCTL_RTMAXCACHE
(ip.rtmaxcache)
Integer: trigger level of cached, unreferenced, protocol-cloned routes
which initiates dynamic adaptation (default 128).
ip.process_options
Integer: control IP options processing.
By setting this variable to 0, all IP options in the incoming packets
will be ignored, and the packets will be passed unmodified.
By setting to 1, IP options in the incoming packets will be processed
accordingly.
By setting to 2, an
ICMP
``prohibited by filter''
message will be sent back in response to incoming packets with IP options.
Default is 1.
This
sysctl(8)
variable affects packets destined for a local host as well as packets
forwarded to some other host.
ip.random_id
Boolean: control IP IDs generation behaviour.
Setting this
sysctl(8)
to non-zero causes the ID field in IP packets to be randomized instead of
incremented by 1 with each packet generated.
This closes a minor information leak which allows remote observers to
determine the rate of packet generation on the machine by watching the
counter.
In the same time, on high-speed links, it can decrease the ID reuse
cycle greatly.
Default is 0 (sequential IP IDs).
IPv6 flow IDs and fragment IDs are always random.
ip.maxfragpackets
Integer: maximum number of fragmented packets the host will accept and hold
in the reassembling queue simultaneously.
0 means that the host will not accept any fragmented packets.
-1 means that the host will accept as many fragmented packets as it receives.
ip.maxfragsperpacket
Integer: maximum number of fragments the host will accept and hold
in the reassembling queue for a packet.
0 means that the host will not accept any fragmented packets.
"An Introductory 4.3 BSD Interprocess Communication Tutorial"PS1
7
"An Advanced 4.3 BSD Interprocess Communication Tutorial"PS1
8
CAVEATS
The Internet protocol support is subject to change as
the Internet protocols develop.
Users should not depend
on details of the current implementation, but rather
the services exported.
HISTORY
The
protocol interface appeared in
BSD 4.2
The
``protocol cloning''
code appeared in
Fx 2.1 .