RAW Section: Linux Programmer's Manual (7) Updated: 2 Oct 2025 Index   NAME raw, SOCK_RAW - Linux IPv4 raw sockets   SYNOPSIS #include <sys/socket.h> #include <netinet/in.h> raw_socket = socket(PF_INET, SOCK_RAW, int protocol);   DESCRIPTION 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 A protocol of IPPROTO_RAW implies enabled IP_HDRINCL and receives all IP protocols. Sending is not allowed. 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. If IP_HDRINCL isn't set then IP header options can be set on raw sockets with see 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 only needed for new protocols or protocols with no user interface (like ICMP). Generating custom TCP or UDP packets using raw sockets is normally unnecessary. 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).   ADDRESS FORMAT Raw sockets use the standard sockaddr_in address structure defined in The sin_port field can be used to specify the IP protocol number, when it is 0 the protocol specified in the initial call is used. See the <netinet/in.h> include file for valid IP protocols.   SOCKET OPTIONS Raw socket options can be set with and read with 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 SOL_IP socket options valid for datagram sockets are supported.   NOTES Raw sockets fragment a packet when its total length exceeds the interface MTU. A more network friendly and faster alternative is to implement path MTU discovery as described in the IP_PMTU_DISCOVER section of A raw socket can be bound to a specific local address using the 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 An IPPROTO_RAW socket is send only. If you really want to receive all IP packets use a 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 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.   ERROR HANDLING 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.   ERRORS EMSGSIZE Packet too big. Either Path MTU Discovery is enabled (the IP_PMTU_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.   VERSIONS 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.   BUGS 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.   AUTHORS This man page was writen by Andi Kleen.   SEE ALSO RFC1191 for path MTU discovery. RFC791 and the <linux/ip.h> include file for the IP protocol.   Index NAME SYNOPSIS DESCRIPTION ADDRESS FORMAT SOCKET OPTIONS NOTES ERROR HANDLING ERRORS VERSIONS BUGS AUTHORS SEE ALSO This document was created by using the manual pages. Time: 12:14:03 GMT, March 24, 2025