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packet (4)
  • >> packet (4) ( Linux man: Специальные файлы /dev/* )
  • packet (7) ( Русские man: Макропакеты и соглашения )
  • packet (7) ( Linux man: Макропакеты и соглашения )
  • Ключ packet обнаружен в базе ключевых слов.


    packet, PF_PACKET - packet interface on device level. 



    #include <sys/socket.h>
    #include <sys/if_packet.h> packet_socket = socket(PF_PACKET, socket_type, protocol);


    Packet sockets are used to receive or send raw packets on the device driver (OSI Layer 2) level. They allow the user to implement protocol modules in user space on top of the physical layer.

    socket_type is either SOCK_RAW for raw packets including the link level header or SOCK_DGRAM for cooked packets with the link level header removed. The link level header informations are available in a common format in a sockaddr_ll. protocol is the IEEE 802.3 protocol number in network order. See the <sys/if_ether.h> include file for a list of allowed protocols. All incoming packets with that protocol will be first passed to the packet socket, after that to the other protocols implemented in the kernel.
      Only processes with effective uid 0 or the CAP_NET_RAW attribute set may open packet sockets.

    There are two types of packet sockets: SOCK_RAW and SOCK_DGRAM. SOCK_RAW is directly passed to and from the device driver without any changes in the packet data. The user program has to know about the physical header structure of the device to properly set up and parse the packet. The address is still parsed and passed in a standard sockaddr_ll address structure. SOCK_RAW is similar but not compatible to the obsolete SOCK_PACKET of Linux 2.0.

    SOCK_DGRAM operates on a slightly higher level. The physical header is removed before passing the packet to the user (and prepended before sending it).

    Per default all packets with the specified protocol received from any interface are passed to a packet socket. To only get packets from a specific interface use bind(2) with a sockaddr_ll address to bind the packet to an interface.

    For sending to SOCK_RAW sockets the user supplied buffer has to contain the complete packet including the physical layer header. That packet is then queued unmodified to the network driver of the interface defined by the destination address. Packets sent through a SOCK_DGRAM packet socket get a suitable physical layer header based on the information in the sockaddr_ll destination address before they are queued.



    The sockaddr_ll is a device independent physical layer address.

    struct sockaddr_ll
        unsigned short  sll_family; /* Always AF_PACKET */
        unsigned short  sll_protocol;/* Physical layer protocol in network order */
        int                         sll_ifindex;/* Interface number */
        unsigned short  sll_hatype; /* Header type */
        unsigned char   sll_pkttype;/* Packet type */
        unsigned char   sll_halen;  /* Length of address */ 
        unsigned char   sll_addr[8];/* Physical layer address */

    sll_protocol is standard ethernet protocol type in network order as defined in the sys/if_ether.h include file. sll_hatype is a ARP type as defined in the sys/if_arp.h include file. sll_pkttype contains the packet type. Valid types are PACKET_HOST for a packet addressed to the local host, PACKET_BROADCAST for a physical layer broadcasted packet, PACKET_MULTICAST for a packet sent to a physical layer multicast address, PACKET_OTHERHOST for a packet to some other host that has been caught by a device driver in promiscuous mode, and PACKET_OUTGOING for a packet originated from the local host that is looped back to a packet socket. sll_halen and sll_addr contain the physical layer (e.g. IEEE 802.3) address and its length.



    Linux 2.2 supports a new way to configure physical layer multicasting and promiscuous mode over packet sockets. It works by calling setsockopt(2) on a packet socket for SOL_PACKET and one of the options PACKET_ADD_MEMBERSHIP or PACKET_DROP_MEMBERSHIP. They both expect a packet_mreq structure as argument:

    struct packet_mreq
    intmr_ifindex;   /* interface index */
    unsigned shortmr_type;   /* mreq type as defined below */ 
    unsigned shortmr_alen;   /* address length */
    unsigned charmr_address[8];   /* physical layer address */ 

    mr_interface contains the interface index for the interface whose status should be changed. Valid options for mr_type are PACKET_MR_MULTICAST to bind the socket to the physical layer multicast group specified in mr_address and mr_alen, PACKET_MR_PROMISC to enable promiscuous mode on the interface to receive all packets on a shared medium, PACKET_MR_ALLMULTI sets the socket up to receive all multicast packets arriving at the interface. PACKET_DROP_MEMBERSHIP removes the binding or setting.



    These ioctls can be accessed using ioctl(2). The correct syntax is error = ioctl(tcp_socket, ioctl_type, value_ptr);

    SIOCGSTAMP Return a struct timeval with the receive timestamp of the last packet passed to the user. This is useful for accurate round trip time measurements and the like. See setitimer(2) for a description of struct timeval.

    FIOCSETOWN and SIOCSPGRP set the process or process group (negative value) to send SIGIO to when an asynchronous IO operation has finished. Argument is a pid_t.

    FIOCGETOWN and SIOCGPGRP get the current process or process group that receive SIGIOs, or 0 when none is set. Argument is a pid_t.

    In addition you may pass all network device ioctls.



    Packet sockets do no error handling other than errors occurred while passing the packet to the device driver. They don't have the concept of a pending error.



    Linux 2.0 only supported SOCK_RAW as (PF_INET, SOCK_PACKET). This is still supported but deprecated. The main difference between SOCK_RAW and SOCK_PACKET is that that SOCK_PACKET uses the old sockaddr_pkt structure to specify an interface.

    struct sockaddr_pkt
    unsigned short spkt_family;
    unsigned char spkt_device[14];
    unsigned short spkt_protocol;

    spkt_family contains the device type, spkt_protocol is the IEEE 802.3 protocol type as defined in the sys/if_ether.h include. spkt_device is the device name as a null terminated string, e.g. eth0.

    This structure is obsolete and should not be used in new code.



    Interface is not up.

    No interface address passed.

    Unknown device name or interface index specified in interface address.

    Packet is bigger than interface MTU.

    Not enough memory to allocate the packet.

    User passed invalid memory address.

    Invalid argument.

    Interface address contained illegal interface index.

    User doesn't have an effective uid of 0 or the CAP_NET_RAW attribute.

    Unknown multicast group address passed.

    No packet received.



    ip(4), socket(4), socket(2), raw(4)




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