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packet, PF_PACKET - packet interface on device level.
#include <features.h> /* for the glibc version number */
#if __GLIBC__ >= 2 && __GLIBC_MINOR >= 1
#include <net/ethernet.h> /* the L2 protocols */
#include <linux/if_ether.h> /* The L2 protocols */
packet_socket = socket(PF_PACKET, int socket_type, int protocol);
Packet sockets are used to receive or send raw packets at the device
driver (OSI Layer 2) level. They allow the user to implement protocol
modules in user space on top of the physical layer.
The 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 information is available in a
common format in a sockaddr_ll. protocol is the IEEE 802.3 protocol
number in network order. See the <linux/if_ether.h> include file for a
list of allowed protocols. When protocol is set to htons(ETH_P_ALL)
then all protocols are received. All incoming packets of that protocol
type will be passed to the packet socket before they are passed to the
protocols implemented in the kernel.
Only processes with effective uid 0 or the CAP_NET_RAW capability may
open packet sockets.
SOCK_RAW packets are passed to and from the device driver without any
changes in the packet data. When receiving a packet, the address is
still parsed and passed in a standard sockaddr_ll address structure.
When transmitting a packet, the user supplied buffer should contain the
physical layer header. That packet is then queued unmodified to the
network driver of the interface defined by the destination address.
Some device drivers always add other headers. SOCK_RAW is similar to
but not compatible with the obsolete SOCK_PACKET of Linux 2.0.
SOCK_DGRAM operates on a slightly higher level. The physical header is
removed before the packet is passed to the user. 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
By default all packets of the specified protocol type are passed to a
packet socket. To only get packets from a specific interface use
bind(2) specifying an address in a struct sockaddr_ll to bind the
packet socket to an interface. Only the sll_protocol and the
sll_ifindex address fields are used for purposes of binding.
The connect(2) operation is not supported on packet sockets.
The sockaddr_ll is a device independent physical layer address.
unsigned short sll_family; /* Always AF_PACKET */
unsigned short sll_protocol; /* Physical layer protocol */
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; /* Physical layer address */
sll_protocol is the standard ethernet protocol type in network order as
defined in the linux/if_ether.h include file. sll_ifindex is the
interface index of the interface (see netdevice(2) ); 0 matches any
interface (only legal for binding). sll_hatype is a ARP type as
defined in the linux/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 broadcast 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. These types make only sense for receiving. sll_addr and
sll_halen contain the physical layer (e.g. IEEE 802.3) address and its
length. The exact interpretation depends on the device.
Packet sockets can be used to configure physical layer multicasting and
promiscuous mode. It works by calling setsockopt(2) on a packet socket
for SOL_PACKET and one of the options PACKET_ADD_MEMBERSHIP to add a
binding or PACKET_DROP_MEMBERSHIP to drop it. They both expect a
packet_mreq structure as argument:
int mr_ifindex; /* interface index */
unsigned short mr_type; /* action */
unsigned short mr_alen; /* address length */
unsigned char mr_address; /* physical layer address */
mr_ifindex contains the interface index for the interface whose status
should be changed. The mr_type parameter specifies which action to
perform. PACKET_MR_PROMISC enables receiving all packets on a shared
medium - often known as ‘‘promiscuous mode’’, PACKET_MR_MULTICAST binds
the socket to the physical layer multicast group specified in
mr_address and mr_alen, and PACKET_MR_ALLMULTI sets the socket up to
receive all multicast packets arriving at the interface.
In addition the traditional ioctls SIOCSIFFLAGS, SIOCADDMULTI,
SIOCDELMULTI can be used for the same purpose.
SIOCGSTAMP can be used to receive the time stamp of the last received
packet. Argument is a struct timeval.
In addition all standard ioctls defined in netdevice(7) and socket(7)
are valid on packet sockets.
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.
In Linux 2.0, the only way to get a packet socket was by calling
socket(PF_INET, SOCK_PACKET, protocol). This is still supported but
strongly deprecated. The main difference between the two methods is
that SOCK_PACKET uses the old struct sockaddr_pkt to specify an
interface, which doesn’t provide physical layer independence.
unsigned short spkt_family;
unsigned char spkt_device;
unsigned short spkt_protocol;
spkt_family contains the device type, spkt_protocol is the IEEE 802.3
protocol type as defined in <sys/if_ether.h> and 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.
For portable programs it is suggested to use PF_PACKET via pcap(3);
although this only covers a subset of the PF_PACKET features.
The SOCK_DGRAM packet sockets make no attempt to create or parse the
IEEE 802.2 LLC header for a IEEE 802.3 frame. When ETH_P_802_3 is
specified as protocol for sending the kernel creates the 802.3 frame
and fills out the length field; the user has to supply the LLC header
to get a fully conforming packet. Incoming 802.3 packets are not
multiplexed on the DSAP/SSAP protocol fields; instead they are supplied
to the user as protocol ETH_P_802_2 with the LLC header prepended. It
is thus not possible to bind to ETH_P_802_3; bind to ETH_P_802_2
instead and do the protocol multiplex yourself. The default for
sending is the standard Ethernet DIX encapsulation with the protocol
Packet sockets are not subject to the input or output firewall chains.
Interface is not up.
No interface address passed.
ENODEV Unknown device name or interface index specified in interface
Packet is bigger than interface MTU.
Not enough memory to allocate the packet.
EFAULT User passed invalid memory address.
EINVAL Invalid argument.
ENXIO Interface address contained illegal interface index.
EPERM User has insufficient privileges to carry out this operation.
Unknown multicast group address passed.
ENOENT No packet received.
In addition other errors may be generated by the low-level
PF_PACKET is a new feature in Linux 2.2. Earlier Linux versions
supported only SOCK_PACKET.
glibc 2.1 does not have a define for SOL_PACKET. The suggested
workaround is to use
#define SOL_PACKET 263
This is fixed in later glibc versions and also does not occur on libc5
The IEEE 802.2/803.3 LLC handling could be considered as a bug.
Socket filters are not documented.
This man page was writen by Andi Kleen with help from Matthew Wilcox.
PF_PACKET in Linux 2.2 was implemented by Alexey Kuznetsov, based on
code by Alan Cox and others.
ip(7), socket(7), socket(2), raw(7), pcap(3).
RFC 894 for the standard IP Ethernet encapsulation.
RFC 1700 for the IEEE 802.3 IP encapsulation.
The linux/if_ether.h include file for physical layer protocols.