Originální popis anglicky:
raw, SOCK_RAW - Linux IPv4 raw sockets
Návod, kniha: Linux Programmer's Manual
#include <sys/socket.h>
#include <netinet/in.h>
raw_socket = socket(PF_INET, SOCK_RAW, int protocol);
Raw sockets allow new IPv4 protocols to be implemented in user space. A raw
socket receives or sends the raw datagram not including link level headers.
The IPv4 layer generates an IP header when sending a packet unless the
IP_HDRINCL socket option is enabled on the socket. When it is enabled,
the packet must contain an IP header. For receiving the IP header is always
included in the packet.
Only processes with an effective user id of 0 or the
CAP_NET_RAW
capability are allowed to open raw sockets.
All packets or errors matching the
protocol number specified for the raw
socket are passed to this socket. For a list of the allowed protocols see
RFC1700 assigned numbers and
getprotobyname(3).
A protocol of
IPPROTO_RAW implies enabled
IP_HDRINCL and is able
to send any IP protocol that is specified in the passed header. Receiving of
all IP protocols via
IPPROTO_RAW is not possible using raw sockets.
| IP Header fields modified on sending by IP_HDRINCL |
|
| IP Checksum |
Always filled in. |
| Source Address |
Filled in when zero. |
| Packet Id |
Filled in when zero. |
| Total Length |
Always filled in. |
If
IP_HDRINCL is specified and the IP header has a non-zero destination
address then the destination address of the socket is used to route the
packet. When
MSG_DONTROUTE is specified the destination address should
refer to a local interface, otherwise a routing table lookup is done anyways
but gatewayed routes are ignored.
If
IP_HDRINCL isn't set then IP header options can be set on raw sockets
with
setsockopt(2); see
ip(7) for more information.
In Linux 2.2 all IP header fields and options can be set using IP socket
options. This means raw sockets are usually only needed for new protocols or
protocols with no user interface (like ICMP).
When a packet is received, it is passed to any raw sockets which have been bound
to its protocol before it is passed to other protocol handlers (e.g. kernel
protocol modules).
Raw sockets use the standard
sockaddr_in address structure defined in
ip(7). The The
sin_port field could be used to specify the IP
protocol number, but it is ignored for sending in Linux 2.2 and should be
always set to 0 (see BUGS) For incoming packets
sin_port is set to the
protocol of the packet. See the
<netinet/in.h> include file for
valid IP protocols.
Raw socket options can be set with
setsockopt(2) and read with
getsockopt(2) by passing the
SOL_RAW family flag.
- ICMP_FILTER
- Enable a special filter for raw sockets bound to the
IPPROTO_ICMP protocol. The value has a bit set for each ICMP
message type which should be filtered out. The default is to filter no
ICMP messages.
In addition all
ip(7)
SOL_IP socket options valid for datagram
sockets are supported.
Raw sockets fragment a packet when its total length exceeds the interface MTU
(but see BUGS). A more network friendly and faster alternative is to implement
path MTU discovery as described in the
IP_MTU_DISCOVER section of
ip(7).
A raw socket can be bound to a specific local address using the
bind(2)
call. If it isn't bound all packets with the specified IP protocol are
received. In addition a RAW socket can be bound to a specific network device
using
SO_BINDTODEVICE; see
socket(7).
An
IPPROTO_RAW socket is send only. If you really want to receive all IP
packets use a
packet(7) socket with the
ETH_P_IP protocol. Note
that packet sockets don't reassemble IP fragments, unlike raw sockets.
If you want to receive all ICMP packets for a datagram socket it is often better
to use
IP_RECVERR on that particular socket; see
ip(7).
Raw sockets may tap all IP protocols in Linux, even protocols like ICMP or TCP
which have a protocol module in the kernel. In this case the packets are
passed to both the kernel module and the raw socket(s). This should not be
relied upon in portable programs, many other BSD socket implementation have
limitations here.
Linux never changes headers passed from the user (except for filling in some
zeroed fields as described for
IP_HDRINCL). This differs from many
other implementations of raw sockets.
RAW sockets are generally rather unportable and should be avoided in programs
intended to be portable.
Sending on raw sockets should take the IP protocol from
sin_port; this
ability was lost in Linux 2.2. Work around is to use
IP_HDRINCL.
Errors originating from the network are only passed to the user when the socket
is connected or the
IP_RECVERR flag is enabled. For connected sockets
only
EMSGSIZE and
EPROTO are passed for compatibility. With
IP_RECVERR all network errors are saved in the error queue.
- EMSGSIZE
- Packet too big. Either Path MTU Discovery is enabled (the
IP_MTU_DISCOVER socket flag) or the packet size exceeds the maximum
allowed IPv4 packet size of 64KB.
- EACCES
- User tried to send to a broadcast address without having
the broadcast flag set on the socket.
- EPROTO
- An ICMP error has arrived reporting a parameter
problem.
- EFAULT
- An invalid memory address was supplied.
- EOPNOTSUPP
- Invalid flag has been passed to a socket call (like
MSG_OOB).
- EINVAL
- Invalid argument.
- EPERM
- The user doesn't have permission to open raw sockets. Only
processes with a effective user id of 0 or the CAP_NET_RAW
attribute may do that.
IP_RECVERR and
ICMP_FILTER are new in Linux 2.2. They are Linux
extensions and should not be used in portable programs.
Linux 2.0 enabled some bug-to-bug compatibility with BSD in the raw socket code
when the SO_BSDCOMPAT flag was set - that has been removed in 2.2.
Transparent proxy extensions are not described.
When the
IP_HDRINCL option is set datagrams will not be fragmented and
are limited to the interface MTU. This is a limitation in Linux 2.2.
Setting the IP protocol for sending in
sin_port got lost in Linux 2.2.
The protocol that socket was bound to or that was specified in the initial
socket(2) call is always used.
This man page was written by Andi Kleen.
recvmsg(2),
sendmsg(2),
capabilities(7),
ip(7),
socket(7)
RFC1191 for path MTU discovery.
RFC791 and the
<linux/ip.h> include file for the IP
protocol.
