c26544aa7f
packets at all. Swapping byte order on SOCK_RAW was actually a bug, an artifact from the BSD network stack, that used to convert a packet to native byte order once it is received by kernel. Other operating systems didn't follow this, and later other BSD descendants fixed this, leaving us alone with the bug. Now it is clear that we should fix the bug. In collaboration with: Olivier Cochard-Labbé <olivier cochard.me> See also: https://wiki.freebsd.org/SOCK_RAW Sponsored by: Nginx, Inc.
904 lines
24 KiB
Groff
904 lines
24 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)ip.4 8.2 (Berkeley) 11/30/93
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd September 1, 2014
|
|
.Dt IP 4
|
|
.Os
|
|
.Sh NAME
|
|
.Nm ip
|
|
.Nd Internet Protocol
|
|
.Sh SYNOPSIS
|
|
.In sys/types.h
|
|
.In sys/socket.h
|
|
.In netinet/in.h
|
|
.Ft int
|
|
.Fn socket AF_INET SOCK_RAW proto
|
|
.Sh DESCRIPTION
|
|
.Tn IP
|
|
is the transport layer protocol used
|
|
by the Internet protocol family.
|
|
Options may be set at the
|
|
.Tn IP
|
|
level
|
|
when using higher-level protocols that are based on
|
|
.Tn IP
|
|
(such as
|
|
.Tn TCP
|
|
and
|
|
.Tn UDP ) .
|
|
It may also be accessed
|
|
through a
|
|
.Dq raw socket
|
|
when developing new protocols, or
|
|
special-purpose applications.
|
|
.Pp
|
|
There are several
|
|
.Tn IP-level
|
|
.Xr setsockopt 2
|
|
and
|
|
.Xr getsockopt 2
|
|
options.
|
|
.Dv IP_OPTIONS
|
|
may be used to provide
|
|
.Tn IP
|
|
options to be transmitted in the
|
|
.Tn IP
|
|
header of each outgoing packet
|
|
or to examine the header options on incoming packets.
|
|
.Tn IP
|
|
options may be used with any socket type in the Internet family.
|
|
The format of
|
|
.Tn IP
|
|
options to be sent is that specified by the
|
|
.Tn IP
|
|
protocol specification (RFC-791), with one exception:
|
|
the list of addresses for Source Route options must include the first-hop
|
|
gateway at the beginning of the list of gateways.
|
|
The first-hop gateway address will be extracted from the option list
|
|
and the size adjusted accordingly before use.
|
|
To disable previously specified options,
|
|
use a zero-length buffer:
|
|
.Bd -literal
|
|
setsockopt(s, IPPROTO_IP, IP_OPTIONS, NULL, 0);
|
|
.Ed
|
|
.Pp
|
|
.Dv IP_TOS
|
|
and
|
|
.Dv IP_TTL
|
|
may be used to set the type-of-service and time-to-live
|
|
fields in the
|
|
.Tn IP
|
|
header for
|
|
.Dv SOCK_STREAM , SOCK_DGRAM ,
|
|
and certain types of
|
|
.Dv SOCK_RAW
|
|
sockets.
|
|
For example,
|
|
.Bd -literal
|
|
int tos = IPTOS_LOWDELAY; /* see <netinet/ip.h> */
|
|
setsockopt(s, IPPROTO_IP, IP_TOS, &tos, sizeof(tos));
|
|
|
|
int ttl = 60; /* max = 255 */
|
|
setsockopt(s, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
|
|
.Ed
|
|
.Pp
|
|
.Dv IP_MINTTL
|
|
may be used to set the minimum acceptable TTL a packet must have when
|
|
received on a socket.
|
|
All packets with a lower TTL are silently dropped.
|
|
This option is only really useful when set to 255, preventing packets
|
|
from outside the directly connected networks reaching local listeners
|
|
on sockets.
|
|
.Pp
|
|
.Dv IP_DONTFRAG
|
|
may be used to set the Don't Fragment flag on IP packets.
|
|
Currently this option is respected only on
|
|
.Xr udp 4
|
|
and raw
|
|
.Xr ip 4
|
|
sockets, unless the
|
|
.Dv IP_HDRINCL
|
|
option has been set.
|
|
On
|
|
.Xr tcp 4
|
|
sockets, the Don't Fragment flag is controlled by the Path
|
|
MTU Discovery option.
|
|
Sending a packet larger than the MTU size of the egress interface,
|
|
determined by the destination address, returns an
|
|
.Er EMSGSIZE
|
|
error.
|
|
.Pp
|
|
If the
|
|
.Dv IP_RECVDSTADDR
|
|
option is enabled on a
|
|
.Dv SOCK_DGRAM
|
|
socket,
|
|
the
|
|
.Xr recvmsg 2
|
|
call will return the destination
|
|
.Tn IP
|
|
address for a
|
|
.Tn UDP
|
|
datagram.
|
|
The
|
|
.Vt msg_control
|
|
field in the
|
|
.Vt msghdr
|
|
structure points to a buffer
|
|
that contains a
|
|
.Vt cmsghdr
|
|
structure followed by the
|
|
.Tn IP
|
|
address.
|
|
The
|
|
.Vt cmsghdr
|
|
fields have the following values:
|
|
.Bd -literal
|
|
cmsg_len = CMSG_LEN(sizeof(struct in_addr))
|
|
cmsg_level = IPPROTO_IP
|
|
cmsg_type = IP_RECVDSTADDR
|
|
.Ed
|
|
.Pp
|
|
The source address to be used for outgoing
|
|
.Tn UDP
|
|
datagrams on a socket can be specified as ancillary data with a type code of
|
|
.Dv IP_SENDSRCADDR .
|
|
The msg_control field in the msghdr structure should point to a buffer
|
|
that contains a
|
|
.Vt cmsghdr
|
|
structure followed by the
|
|
.Tn IP
|
|
address.
|
|
The cmsghdr fields should have the following values:
|
|
.Bd -literal
|
|
cmsg_len = CMSG_LEN(sizeof(struct in_addr))
|
|
cmsg_level = IPPROTO_IP
|
|
cmsg_type = IP_SENDSRCADDR
|
|
.Ed
|
|
.Pp
|
|
The socket should be either bound to
|
|
.Dv INADDR_ANY
|
|
and a local port, and the address supplied with
|
|
.Dv IP_SENDSRCADDR
|
|
should't be
|
|
.Dv INADDR_ANY ,
|
|
or the socket should be bound to a local address and the address supplied with
|
|
.Dv IP_SENDSRCADDR
|
|
should be
|
|
.Dv INADDR_ANY .
|
|
In the latter case bound address is overriden via generic source address
|
|
selection logic, which would choose IP address of interface closest to
|
|
destination.
|
|
.Pp
|
|
For convenience,
|
|
.Dv IP_SENDSRCADDR
|
|
is defined to have the same value as
|
|
.Dv IP_RECVDSTADDR ,
|
|
so the
|
|
.Dv IP_RECVDSTADDR
|
|
control message from
|
|
.Xr recvmsg 2
|
|
can be used directly as a control message for
|
|
.Xr sendmsg 2 .
|
|
.\"
|
|
.Pp
|
|
If the
|
|
.Dv IP_ONESBCAST
|
|
option is enabled on a
|
|
.Dv SOCK_DGRAM
|
|
or a
|
|
.Dv SOCK_RAW
|
|
socket, the destination address of outgoing
|
|
broadcast datagrams on that socket will be forced
|
|
to the undirected broadcast address,
|
|
.Dv INADDR_BROADCAST ,
|
|
before transmission.
|
|
This is in contrast to the default behavior of the
|
|
system, which is to transmit undirected broadcasts
|
|
via the first network interface with the
|
|
.Dv IFF_BROADCAST
|
|
flag set.
|
|
.Pp
|
|
This option allows applications to choose which
|
|
interface is used to transmit an undirected broadcast
|
|
datagram.
|
|
For example, the following code would force an
|
|
undirected broadcast to be transmitted via the interface
|
|
configured with the broadcast address 192.168.2.255:
|
|
.Bd -literal
|
|
char msg[512];
|
|
struct sockaddr_in sin;
|
|
int onesbcast = 1; /* 0 = disable (default), 1 = enable */
|
|
|
|
setsockopt(s, IPPROTO_IP, IP_ONESBCAST, &onesbcast, sizeof(onesbcast));
|
|
sin.sin_addr.s_addr = inet_addr("192.168.2.255");
|
|
sin.sin_port = htons(1234);
|
|
sendto(s, msg, sizeof(msg), 0, &sin, sizeof(sin));
|
|
.Ed
|
|
.Pp
|
|
It is the application's responsibility to set the
|
|
.Dv IP_TTL
|
|
option
|
|
to an appropriate value in order to prevent broadcast storms.
|
|
The application must have sufficient credentials to set the
|
|
.Dv SO_BROADCAST
|
|
socket level option, otherwise the
|
|
.Dv IP_ONESBCAST
|
|
option has no effect.
|
|
.Pp
|
|
If the
|
|
.Dv IP_BINDANY
|
|
option is enabled on a
|
|
.Dv SOCK_STREAM ,
|
|
.Dv SOCK_DGRAM
|
|
or a
|
|
.Dv SOCK_RAW
|
|
socket, one can
|
|
.Xr bind 2
|
|
to any address, even one not bound to any available network interface in the
|
|
system.
|
|
This functionality (in conjunction with special firewall rules) can be used for
|
|
implementing a transparent proxy.
|
|
The
|
|
.Dv PRIV_NETINET_BINDANY
|
|
privilege is needed to set this option.
|
|
.Pp
|
|
If the
|
|
.Dv IP_RECVTTL
|
|
option is enabled on a
|
|
.Dv SOCK_DGRAM
|
|
socket, the
|
|
.Xr recvmsg 2
|
|
call will return the
|
|
.Tn IP
|
|
.Tn TTL
|
|
(time to live) field for a
|
|
.Tn UDP
|
|
datagram.
|
|
The msg_control field in the msghdr structure points to a buffer
|
|
that contains a cmsghdr structure followed by the
|
|
.Tn TTL .
|
|
The cmsghdr fields have the following values:
|
|
.Bd -literal
|
|
cmsg_len = CMSG_LEN(sizeof(u_char))
|
|
cmsg_level = IPPROTO_IP
|
|
cmsg_type = IP_RECVTTL
|
|
.Ed
|
|
.\"
|
|
.Pp
|
|
If the
|
|
.Dv IP_RECVTOS
|
|
option is enabled on a
|
|
.Dv SOCK_DGRAM
|
|
socket, the
|
|
.Xr recvmsg 2
|
|
call will return the
|
|
.Tn IP
|
|
.Tn TOS
|
|
(type of service) field for a
|
|
.Tn UDP
|
|
datagram.
|
|
The msg_control field in the msghdr structure points to a buffer
|
|
that contains a cmsghdr structure followed by the
|
|
.Tn TOS .
|
|
The cmsghdr fields have the following values:
|
|
.Bd -literal
|
|
cmsg_len = CMSG_LEN(sizeof(u_char))
|
|
cmsg_level = IPPROTO_IP
|
|
cmsg_type = IP_RECVTOS
|
|
.Ed
|
|
.\"
|
|
.Pp
|
|
If the
|
|
.Dv IP_RECVIF
|
|
option is enabled on a
|
|
.Dv SOCK_DGRAM
|
|
socket, the
|
|
.Xr recvmsg 2
|
|
call returns a
|
|
.Vt "struct sockaddr_dl"
|
|
corresponding to the interface on which the
|
|
packet was received.
|
|
The
|
|
.Va msg_control
|
|
field in the
|
|
.Vt msghdr
|
|
structure points to a buffer that contains a
|
|
.Vt cmsghdr
|
|
structure followed by the
|
|
.Vt "struct sockaddr_dl" .
|
|
The
|
|
.Vt cmsghdr
|
|
fields have the following values:
|
|
.Bd -literal
|
|
cmsg_len = CMSG_LEN(sizeof(struct sockaddr_dl))
|
|
cmsg_level = IPPROTO_IP
|
|
cmsg_type = IP_RECVIF
|
|
.Ed
|
|
.Pp
|
|
.Dv IP_PORTRANGE
|
|
may be used to set the port range used for selecting a local port number
|
|
on a socket with an unspecified (zero) port number.
|
|
It has the following
|
|
possible values:
|
|
.Bl -tag -width IP_PORTRANGE_DEFAULT
|
|
.It Dv IP_PORTRANGE_DEFAULT
|
|
use the default range of values, normally
|
|
.Dv IPPORT_HIFIRSTAUTO
|
|
through
|
|
.Dv IPPORT_HILASTAUTO .
|
|
This is adjustable through the sysctl setting:
|
|
.Va net.inet.ip.portrange.first
|
|
and
|
|
.Va net.inet.ip.portrange.last .
|
|
.It Dv IP_PORTRANGE_HIGH
|
|
use a high range of values, normally
|
|
.Dv IPPORT_HIFIRSTAUTO
|
|
and
|
|
.Dv IPPORT_HILASTAUTO .
|
|
This is adjustable through the sysctl setting:
|
|
.Va net.inet.ip.portrange.hifirst
|
|
and
|
|
.Va net.inet.ip.portrange.hilast .
|
|
.It Dv IP_PORTRANGE_LOW
|
|
use a low range of ports, which are normally restricted to
|
|
privileged processes on
|
|
.Ux
|
|
systems.
|
|
The range is normally from
|
|
.Dv IPPORT_RESERVED
|
|
\- 1 down to
|
|
.Li IPPORT_RESERVEDSTART
|
|
in descending order.
|
|
This is adjustable through the sysctl setting:
|
|
.Va net.inet.ip.portrange.lowfirst
|
|
and
|
|
.Va net.inet.ip.portrange.lowlast .
|
|
.El
|
|
.Pp
|
|
The range of privileged ports which only may be opened by
|
|
root-owned processes may be modified by the
|
|
.Va net.inet.ip.portrange.reservedlow
|
|
and
|
|
.Va net.inet.ip.portrange.reservedhigh
|
|
sysctl settings.
|
|
The values default to the traditional range,
|
|
0 through
|
|
.Dv IPPORT_RESERVED
|
|
\- 1
|
|
(0 through 1023), respectively.
|
|
Note that these settings do not affect and are not accounted for in the
|
|
use or calculation of the other
|
|
.Va net.inet.ip.portrange
|
|
values above.
|
|
Changing these values departs from
|
|
.Ux
|
|
tradition and has security
|
|
consequences that the administrator should carefully evaluate before
|
|
modifying these settings.
|
|
.Pp
|
|
Ports are allocated at random within the specified port range in order
|
|
to increase the difficulty of random spoofing attacks.
|
|
In scenarios such as benchmarking, this behavior may be undesirable.
|
|
In these cases,
|
|
.Va net.inet.ip.portrange.randomized
|
|
can be used to toggle randomization off.
|
|
If more than
|
|
.Va net.inet.ip.portrange.randomcps
|
|
ports have been allocated in the last second, then return to sequential
|
|
port allocation.
|
|
Return to random allocation only once the current port allocation rate
|
|
drops below
|
|
.Va net.inet.ip.portrange.randomcps
|
|
for at least
|
|
.Va net.inet.ip.portrange.randomtime
|
|
seconds.
|
|
The default values for
|
|
.Va net.inet.ip.portrange.randomcps
|
|
and
|
|
.Va net.inet.ip.portrange.randomtime
|
|
are 10 port allocations per second and 45 seconds correspondingly.
|
|
.Ss "Multicast Options"
|
|
.Tn IP
|
|
multicasting is supported only on
|
|
.Dv AF_INET
|
|
sockets of type
|
|
.Dv SOCK_DGRAM
|
|
and
|
|
.Dv SOCK_RAW ,
|
|
and only on networks where the interface
|
|
driver supports multicasting.
|
|
.Pp
|
|
The
|
|
.Dv IP_MULTICAST_TTL
|
|
option changes the time-to-live (TTL)
|
|
for outgoing multicast datagrams
|
|
in order to control the scope of the multicasts:
|
|
.Bd -literal
|
|
u_char ttl; /* range: 0 to 255, default = 1 */
|
|
setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
|
|
.Ed
|
|
.Pp
|
|
Datagrams with a TTL of 1 are not forwarded beyond the local network.
|
|
Multicast datagrams with a TTL of 0 will not be transmitted on any network,
|
|
but may be delivered locally if the sending host belongs to the destination
|
|
group and if multicast loopback has not been disabled on the sending socket
|
|
(see below).
|
|
Multicast datagrams with TTL greater than 1 may be forwarded
|
|
to other networks if a multicast router is attached to the local network.
|
|
.Pp
|
|
For hosts with multiple interfaces, where an interface has not
|
|
been specified for a multicast group membership,
|
|
each multicast transmission is sent from the primary network interface.
|
|
The
|
|
.Dv IP_MULTICAST_IF
|
|
option overrides the default for
|
|
subsequent transmissions from a given socket:
|
|
.Bd -literal
|
|
struct in_addr addr;
|
|
setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF, &addr, sizeof(addr));
|
|
.Ed
|
|
.Pp
|
|
where "addr" is the local
|
|
.Tn IP
|
|
address of the desired interface or
|
|
.Dv INADDR_ANY
|
|
to specify the default interface.
|
|
.Pp
|
|
To specify an interface by index, an instance of
|
|
.Vt ip_mreqn
|
|
may be passed instead.
|
|
The
|
|
.Vt imr_ifindex
|
|
member should be set to the index of the desired interface,
|
|
or 0 to specify the default interface.
|
|
The kernel differentiates between these two structures by their size.
|
|
.Pp
|
|
The use of
|
|
.Vt IP_MULTICAST_IF
|
|
is
|
|
.Em not recommended ,
|
|
as multicast memberships are scoped to each
|
|
individual interface.
|
|
It is supported for legacy use only by applications,
|
|
such as routing daemons, which expect to
|
|
be able to transmit link-local IPv4 multicast datagrams (224.0.0.0/24)
|
|
on multiple interfaces,
|
|
without requesting an individual membership for each interface.
|
|
.Pp
|
|
.\"
|
|
An interface's local IP address and multicast capability can
|
|
be obtained via the
|
|
.Dv SIOCGIFCONF
|
|
and
|
|
.Dv SIOCGIFFLAGS
|
|
ioctls.
|
|
Normal applications should not need to use this option.
|
|
.Pp
|
|
If a multicast datagram is sent to a group to which the sending host itself
|
|
belongs (on the outgoing interface), a copy of the datagram is, by default,
|
|
looped back by the IP layer for local delivery.
|
|
The
|
|
.Dv IP_MULTICAST_LOOP
|
|
option gives the sender explicit control
|
|
over whether or not subsequent datagrams are looped back:
|
|
.Bd -literal
|
|
u_char loop; /* 0 = disable, 1 = enable (default) */
|
|
setsockopt(s, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop));
|
|
.Ed
|
|
.Pp
|
|
This option
|
|
improves performance for applications that may have no more than one
|
|
instance on a single host (such as a routing daemon), by eliminating
|
|
the overhead of receiving their own transmissions.
|
|
It should generally not
|
|
be used by applications for which there may be more than one instance on a
|
|
single host (such as a conferencing program) or for which the sender does
|
|
not belong to the destination group (such as a time querying program).
|
|
.Pp
|
|
The sysctl setting
|
|
.Va net.inet.ip.mcast.loop
|
|
controls the default setting of the
|
|
.Dv IP_MULTICAST_LOOP
|
|
socket option for new sockets.
|
|
.Pp
|
|
A multicast datagram sent with an initial TTL greater than 1 may be delivered
|
|
to the sending host on a different interface from that on which it was sent,
|
|
if the host belongs to the destination group on that other interface.
|
|
The loopback control option has no effect on such delivery.
|
|
.Pp
|
|
A host must become a member of a multicast group before it can receive
|
|
datagrams sent to the group.
|
|
To join a multicast group, use the
|
|
.Dv IP_ADD_MEMBERSHIP
|
|
option:
|
|
.Bd -literal
|
|
struct ip_mreq mreq;
|
|
setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));
|
|
.Ed
|
|
.Pp
|
|
where
|
|
.Fa mreq
|
|
is the following structure:
|
|
.Bd -literal
|
|
struct ip_mreq {
|
|
struct in_addr imr_multiaddr; /* IP multicast address of group */
|
|
struct in_addr imr_interface; /* local IP address of interface */
|
|
}
|
|
.Ed
|
|
.Pp
|
|
.Va imr_interface
|
|
should be set to the
|
|
.Tn IP
|
|
address of a particular multicast-capable interface if
|
|
the host is multihomed.
|
|
It may be set to
|
|
.Dv INADDR_ANY
|
|
to choose the default interface, although this is not recommended;
|
|
this is considered to be the first interface corresponding
|
|
to the default route.
|
|
Otherwise, the first multicast-capable interface
|
|
configured in the system will be used.
|
|
.Pp
|
|
Prior to
|
|
.Fx 7.0 ,
|
|
if the
|
|
.Va imr_interface
|
|
member is within the network range
|
|
.Li 0.0.0.0/8 ,
|
|
it is treated as an interface index in the system interface MIB,
|
|
as per the RIP Version 2 MIB Extension (RFC-1724).
|
|
In versions of
|
|
.Fx
|
|
since 7.0, this behavior is no longer supported.
|
|
Developers should
|
|
instead use the RFC 3678 multicast source filter APIs; in particular,
|
|
.Dv MCAST_JOIN_GROUP .
|
|
.Pp
|
|
Up to
|
|
.Dv IP_MAX_MEMBERSHIPS
|
|
memberships may be added on a single socket.
|
|
Membership is associated with a single interface;
|
|
programs running on multihomed hosts may need to
|
|
join the same group on more than one interface.
|
|
.Pp
|
|
To drop a membership, use:
|
|
.Bd -literal
|
|
struct ip_mreq mreq;
|
|
setsockopt(s, IPPROTO_IP, IP_DROP_MEMBERSHIP, &mreq, sizeof(mreq));
|
|
.Ed
|
|
.Pp
|
|
where
|
|
.Fa mreq
|
|
contains the same values as used to add the membership.
|
|
Memberships are dropped when the socket is closed or the process exits.
|
|
.\" TODO: Update this piece when IPv4 source-address selection is implemented.
|
|
.Pp
|
|
The IGMP protocol uses the primary IP address of the interface
|
|
as its identifier for group membership.
|
|
This is the first IP address configured on the interface.
|
|
If this address is removed or changed, the results are
|
|
undefined, as the IGMP membership state will then be inconsistent.
|
|
If multiple IP aliases are configured on the same interface,
|
|
they will be ignored.
|
|
.Pp
|
|
This shortcoming was addressed in IPv6; MLDv2 requires
|
|
that the unique link-local address for an interface is
|
|
used to identify an MLDv2 listener.
|
|
.Ss "Source-Specific Multicast Options"
|
|
Since
|
|
.Fx 8.0 ,
|
|
the use of Source-Specific Multicast (SSM) is supported.
|
|
These extensions require an IGMPv3 multicast router in order to
|
|
make best use of them.
|
|
If a legacy multicast router is present on the link,
|
|
.Fx
|
|
will simply downgrade to the version of IGMP spoken by the router,
|
|
and the benefits of source filtering on the upstream link
|
|
will not be present, although the kernel will continue to
|
|
squelch transmissions from blocked sources.
|
|
.Pp
|
|
Each group membership on a socket now has a filter mode:
|
|
.Bl -tag -width MCAST_EXCLUDE
|
|
.It Dv MCAST_EXCLUDE
|
|
Datagrams sent to this group are accepted,
|
|
unless the source is in a list of blocked source addresses.
|
|
.It Dv MCAST_INCLUDE
|
|
Datagrams sent to this group are accepted
|
|
only if the source is in a list of accepted source addresses.
|
|
.El
|
|
.Pp
|
|
Groups joined using the legacy
|
|
.Dv IP_ADD_MEMBERSHIP
|
|
option are placed in exclusive-mode,
|
|
and are able to request that certain sources are blocked or allowed.
|
|
This is known as the
|
|
.Em delta-based API .
|
|
.Pp
|
|
To block a multicast source on an existing group membership:
|
|
.Bd -literal
|
|
struct ip_mreq_source mreqs;
|
|
setsockopt(s, IPPROTO_IP, IP_BLOCK_SOURCE, &mreqs, sizeof(mreqs));
|
|
.Ed
|
|
.Pp
|
|
where
|
|
.Fa mreqs
|
|
is the following structure:
|
|
.Bd -literal
|
|
struct ip_mreq_source {
|
|
struct in_addr imr_multiaddr; /* IP multicast address of group */
|
|
struct in_addr imr_sourceaddr; /* IP address of source */
|
|
struct in_addr imr_interface; /* local IP address of interface */
|
|
}
|
|
.Ed
|
|
.Va imr_sourceaddr
|
|
should be set to the address of the source to be blocked.
|
|
.Pp
|
|
To unblock a multicast source on an existing group:
|
|
.Bd -literal
|
|
struct ip_mreq_source mreqs;
|
|
setsockopt(s, IPPROTO_IP, IP_UNBLOCK_SOURCE, &mreqs, sizeof(mreqs));
|
|
.Ed
|
|
.Pp
|
|
The
|
|
.Dv IP_BLOCK_SOURCE
|
|
and
|
|
.Dv IP_UNBLOCK_SOURCE
|
|
options are
|
|
.Em not permitted
|
|
for inclusive-mode group memberships.
|
|
.Pp
|
|
To join a multicast group in
|
|
.Dv MCAST_INCLUDE
|
|
mode with a single source,
|
|
or add another source to an existing inclusive-mode membership:
|
|
.Bd -literal
|
|
struct ip_mreq_source mreqs;
|
|
setsockopt(s, IPPROTO_IP, IP_ADD_SOURCE_MEMBERSHIP, &mreqs, sizeof(mreqs));
|
|
.Ed
|
|
.Pp
|
|
To leave a single source from an existing group in inclusive mode:
|
|
.Bd -literal
|
|
struct ip_mreq_source mreqs;
|
|
setsockopt(s, IPPROTO_IP, IP_DROP_SOURCE_MEMBERSHIP, &mreqs, sizeof(mreqs));
|
|
.Ed
|
|
If this is the last accepted source for the group, the membership
|
|
will be dropped.
|
|
.Pp
|
|
The
|
|
.Dv IP_ADD_SOURCE_MEMBERSHIP
|
|
and
|
|
.Dv IP_DROP_SOURCE_MEMBERSHIP
|
|
options are
|
|
.Em not accepted
|
|
for exclusive-mode group memberships.
|
|
However, both exclusive and inclusive mode memberships
|
|
support the use of the
|
|
.Em full-state API
|
|
documented in RFC 3678.
|
|
For management of source filter lists using this API,
|
|
please refer to
|
|
.Xr sourcefilter 3 .
|
|
.Pp
|
|
The sysctl settings
|
|
.Va net.inet.ip.mcast.maxsocksrc
|
|
and
|
|
.Va net.inet.ip.mcast.maxgrpsrc
|
|
are used to specify an upper limit on the number of per-socket and per-group
|
|
source filter entries which the kernel may allocate.
|
|
.\"-----------------------
|
|
.Ss "Raw IP Sockets"
|
|
Raw
|
|
.Tn IP
|
|
sockets are connectionless,
|
|
and are normally used with the
|
|
.Xr sendto 2
|
|
and
|
|
.Xr recvfrom 2
|
|
calls, though the
|
|
.Xr connect 2
|
|
call may also be used to fix the destination for future
|
|
packets (in which case the
|
|
.Xr read 2
|
|
or
|
|
.Xr recv 2
|
|
and
|
|
.Xr write 2
|
|
or
|
|
.Xr send 2
|
|
system calls may be used).
|
|
.Pp
|
|
If
|
|
.Fa proto
|
|
is 0, the default protocol
|
|
.Dv IPPROTO_RAW
|
|
is used for outgoing
|
|
packets, and only incoming packets destined for that protocol
|
|
are received.
|
|
If
|
|
.Fa proto
|
|
is non-zero, that protocol number will be used on outgoing packets
|
|
and to filter incoming packets.
|
|
.Pp
|
|
Outgoing packets automatically have an
|
|
.Tn IP
|
|
header prepended to
|
|
them (based on the destination address and the protocol
|
|
number the socket is created with),
|
|
unless the
|
|
.Dv IP_HDRINCL
|
|
option has been set.
|
|
Unlike in previous
|
|
.Bx
|
|
releases, incoming packets are received with
|
|
.Tn IP
|
|
header and options intact, leaving all fields in network byte order.
|
|
.Pp
|
|
.Dv IP_HDRINCL
|
|
indicates the complete IP header is included with the data
|
|
and may be used only with the
|
|
.Dv SOCK_RAW
|
|
type.
|
|
.Bd -literal
|
|
#include <netinet/in_systm.h>
|
|
#include <netinet/ip.h>
|
|
|
|
int hincl = 1; /* 1 = on, 0 = off */
|
|
setsockopt(s, IPPROTO_IP, IP_HDRINCL, &hincl, sizeof(hincl));
|
|
.Ed
|
|
.Pp
|
|
Unlike previous
|
|
.Bx
|
|
releases, the program must set all
|
|
the fields of the IP header, including the following:
|
|
.Bd -literal
|
|
ip->ip_v = IPVERSION;
|
|
ip->ip_hl = hlen >> 2;
|
|
ip->ip_id = 0; /* 0 means kernel set appropriate value */
|
|
ip->ip_off = htons(offset);
|
|
ip->ip_len = htons(len);
|
|
.Ed
|
|
.Pp
|
|
The packet should be provided as is to be sent over wire.
|
|
This implies all fields, including
|
|
.Va ip_len
|
|
and
|
|
.Va ip_off
|
|
to be in network byte order.
|
|
See
|
|
.Xr byteorder 3
|
|
for more information on network byte order.
|
|
If the
|
|
.Va ip_id
|
|
field is set to 0 then the kernel will choose an
|
|
appropriate value.
|
|
If the header source address is set to
|
|
.Dv INADDR_ANY ,
|
|
the kernel will choose an appropriate address.
|
|
.Sh ERRORS
|
|
A socket operation may fail with one of the following errors returned:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EISCONN
|
|
when trying to establish a connection on a socket which
|
|
already has one, or when trying to send a datagram with the destination
|
|
address specified and the socket is already connected;
|
|
.It Bq Er ENOTCONN
|
|
when trying to send a datagram, but
|
|
no destination address is specified, and the socket has not been
|
|
connected;
|
|
.It Bq Er ENOBUFS
|
|
when the system runs out of memory for
|
|
an internal data structure;
|
|
.It Bq Er EADDRNOTAVAIL
|
|
when an attempt is made to create a
|
|
socket with a network address for which no network interface
|
|
exists.
|
|
.It Bq Er EACCES
|
|
when an attempt is made to create
|
|
a raw IP socket by a non-privileged process.
|
|
.El
|
|
.Pp
|
|
The following errors specific to
|
|
.Tn IP
|
|
may occur when setting or getting
|
|
.Tn IP
|
|
options:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EINVAL
|
|
An unknown socket option name was given.
|
|
.It Bq Er EINVAL
|
|
The IP option field was improperly formed;
|
|
an option field was shorter than the minimum value
|
|
or longer than the option buffer provided.
|
|
.El
|
|
.Pp
|
|
The following errors may occur when attempting to send
|
|
.Tn IP
|
|
datagrams via a
|
|
.Dq raw socket
|
|
with the
|
|
.Dv IP_HDRINCL
|
|
option set:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EINVAL
|
|
The user-supplied
|
|
.Va ip_len
|
|
field was not equal to the length of the datagram written to the socket.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr getsockopt 2 ,
|
|
.Xr recv 2 ,
|
|
.Xr send 2 ,
|
|
.Xr byteorder 3 ,
|
|
.Xr icmp 4 ,
|
|
.Xr igmp 4 ,
|
|
.Xr inet 4 ,
|
|
.Xr intro 4 ,
|
|
.Xr multicast 4 ,
|
|
.Xr sourcefilter 3
|
|
.Rs
|
|
.%A D. Thaler
|
|
.%A B. Fenner
|
|
.%A B. Quinn
|
|
.%T "Socket Interface Extensions for Multicast Source Filters"
|
|
.%N RFC 3678
|
|
.%D Jan 2004
|
|
.Re
|
|
.Sh HISTORY
|
|
The
|
|
.Nm
|
|
protocol appeared in
|
|
.Bx 4.2 .
|
|
The
|
|
.Vt ip_mreqn
|
|
structure appeared in
|
|
.Tn Linux 2.4 .
|
|
.Sh BUGS
|
|
Before
|
|
.Fx 10.0
|
|
packets received on raw IP sockets had the
|
|
.Va ip_hl
|
|
subtracted from the
|
|
.Va ip_len
|
|
field.
|
|
.Pp
|
|
Before
|
|
.Fx 11.0
|
|
packets received on raw IP sockets had the
|
|
.Va ip_len
|
|
and
|
|
.Va ip_off
|
|
fields converted to host byte order.
|
|
Packets written to raw IP sockets were expected to have
|
|
.Va ip_len
|
|
and
|
|
.Va ip_off
|
|
in host byte order.
|