INET(4) FreeBSD Kernel Interfaces Manual INET(4)
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 alpha, amd64 and i386
these are word and byte reversed). The include file <netinet/in.h>
defines this address as a discriminated union.
Sockets bound to the Internet protocol family utilize the following
addressing structure,
struct sockaddr_in {
uint8_t sin_len;
sa_family_t sin_family;
in_port_t sin_port;
struct in_addr sin_addr;
char sin_zero[8];
};
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 inet address on an interface consist of the address itself, the
netmask, either broadcast address in case of a broadcast interface or
peers address in case of point-to-point interface. The following
ioctl(2) commands are provided for a datagram socket in the Internet
domain:
SIOCAIFADDR Add address to an interface. The command
requires struct in_aliasreq as argument.
SIOCDIFADDR Delete address from an interface. The command
requires struct ifreq as argument.
SIOCGIFADDR
SIOCGIFBRDADDR
SIOCGIFDSTADDR
SIOCGIFNETMASK Return address information from interface. The
returned value is in struct ifreq. This way of
address information retrieval is obsoleted, a
preferred way is to use getifaddrs(3) API.
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_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).
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.rfc6864 Boolean: control IP IDs generation behaviour.
True value enables RFC6864 support, which
specifies that IP ID field of atomic datagrams
can be set to any value. The
FreeBSD implementation sets it to zero. Enabled
by default.
ip.random_id Boolean: control IP IDs generation behaviour.
Setting this sysctl(8) to 1 causes the ID field
in non-atomic IP datagrams (or all IP datagrams,
if ip.rfc6864 is disabled) 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. At 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.maxfrags Integer: maximum number of fragments the host
will accept and simultaneously hold across all
reassembly queues in all VNETs. If set to 0,
reassembly is disabled. If set to -1, this
limit is not applied. This limit is
recalculated when the number of mbuf clusters is
changed. This is a global limit.
ip.maxfragpackets Integer: maximum number of fragmented packets
the host will accept and simultaneously hold in
the reassembly queue for a particular VNET. 0
means that the host will not accept any
fragmented packets for that VNET. -1 means that
the host will not apply this limit for that
VNET. This limit is recalculated when the
number of mbuf clusters is changed. This is a
per-VNET limit.
ip.maxfragbucketsize Integer: maximum number of reassembly queues per
bucket. Fragmented packets are hashed to
buckets. Each bucket has a list of reassembly
queues. The system must compare the incoming
packets to the existing reassembly queues in the
bucket to find a matching reassembly queue. To
preserve system resources, the system limits the
number of reassembly queues allowed in each
bucket. This limit is recalculated when the
number of mbuf clusters is changed or when the
value of ip.maxfragpackets changes. This is a
per-VNET limit.
ip.maxfragsperpacket Integer: maximum number of fragments the host
will accept and hold in the reassembly queue for
a packet. 0 means that the host will not accept
any fragmented packets for the VNET. This is a
per-VNET limit.
SEE ALSO
ioctl(2), socket(2), getifaddrs(3), sysctl(3), icmp(4), intro(4), ip(4),
ipfirewall(4), route(4), tcp(4), udp(4), pfil(9)
"An Introductory 4.3 BSD Interprocess Communication Tutorial", PS1, 7.
"An Advanced 4.3 BSD Interprocess Communication Tutorial", PS1, 8.
HISTORY
The inet protocol interface appeared in 4.2BSD. The "protocol cloning"
code appeared in FreeBSD 2.1.
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.
FreeBSD 13.1-RELEASE-p6 August 14, 2018 FreeBSD 13.1-RELEASE-p6
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