raw - Linux IPv4 raw sockets
#include <sys/socket.h>
#include <netinet/in.h>
raw_socket = socket(AF_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.
In order to create a raw socket, a process must have the CAP_NET_RAW capability in the user namespace that governs its network namespace.
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 the IANA list of assigned protocol numbers at http://www.iana.org/assignments/protocol-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.
TABLE
If IP_HDRINCL is specified and the IP header has a nonzero 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 anyway 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.
Starting with Linux 2.2, all IP header fields and options can be set using IP socket options. This means raw sockets are usually needed only 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).
For sending and receiving datagrams (sendto(2),
recvfrom(2), and similar), raw sockets use the standard
sockaddr_in
address structure defined in
ip(7). The sin_port
field could be used to
specify the IP protocol number, but it is ignored for sending in Linux
2.2 and later, and should be always set to 0 (see BUGS). For incoming
packets, sin_port
is set to zero.
Raw socket options can be set with setsockopt(2) and read with getsockopt(2) by passing the IPPROTO_RAW family flag.
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) IPPROTO_IP socket options valid for datagram sockets are supported.
Errors originating from the network are passed to the user only 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.
recvmsg(2), sendmsg(2), capabilities(7), ip(7), socket(7)
RFC 1191 for path MTU discovery. RFC
791 and the <linux/ip.h>
header file for the IP
protocol.