1PACKET(7) Linux Programmer's Manual PACKET(7)
2
6 packet - packet interface on device level.
7
9 #include <sys/socket.h>
10 #include <netpacket/packet.h>
11 #include <net/ethernet.h> /* the L2 protocols */
12 packet_socket = socket(AF_PACKET, int socket_type, int protocol);
14
16 Packet sockets are used to receive or send raw packets at the device
17 driver (OSI Layer 2) level. They allow the user to implement protocol
18 modules in user space on top of the physical layer.
19 The socket_type is either SOCK_RAW for raw packets including the link
21 level header or SOCK_DGRAM for cooked packets with the link level
22 header removed. The link level header information is available in a
23 common format in a sockaddr_ll. protocol is the IEEE 802.3 protocol
24 number in network order. See the <linux/if_ether.h> include file for a
25 list of allowed protocols. When protocol is set to htons(ETH_P_ALL)
26 then all protocols are received. All incoming packets of that protocol
27 type will be passed to the packet socket before they are passed to the
28 protocols implemented in the kernel.
29 Only processes with effective UID 0 or the CAP_NET_RAW capability may
31 open packet sockets.
32 SOCK_RAW packets are passed to and from the device driver without any
34 changes in the packet data. When receiving a packet, the address is
35 still parsed and passed in a standard sockaddr_ll address structure.
36 When transmitting a packet, the user supplied buffer should contain the
37 physical layer header. That packet is then queued unmodified to the
38 network driver of the interface defined by the destination address.
39 Some device drivers always add other headers. SOCK_RAW is similar to
40 but not compatible with the obsolete AF_INET/SOCK_PACKET of Linux 2.0.
41 SOCK_DGRAM operates on a slightly higher level. The physical header is
43 removed before the packet is passed to the user. Packets sent through
44 a SOCK_DGRAM packet socket get a suitable physical layer header based
45 on the information in the sockaddr_ll destination address before they
46 are queued.
47 By default all packets of the specified protocol type are passed to a
49 packet socket. To get packets only from a specific interface use
50 bind(2) specifying an address in a struct sockaddr_ll to bind the
51 packet socket to an interface. Only the sll_protocol and the
52 sll_ifindex address fields are used for purposes of binding.
53 The connect(2) operation is not supported on packet sockets.
55 When the MSG_TRUNC flag is passed to recvmsg(2), recv(2), recvfrom(2)
57 the real length of the packet on the wire is always returned, even when
58 it is longer than the buffer.
59 Address types
61 The sockaddr_ll is a device independent physical layer address.
62 struct sockaddr_ll {
64 unsigned short sll_family; /* Always AF_PACKET */
65 unsigned short sll_protocol; /* Physical layer protocol */
66 int sll_ifindex; /* Interface number */
67 unsigned short sll_hatype; /* ARP hardware type */
68 unsigned char sll_pkttype; /* Packet type */
69 unsigned char sll_halen; /* Length of address */
70 unsigned char sll_addr[8]; /* Physical layer address */
71 };
72 sll_protocol is the standard ethernet protocol type in network order as
74 defined in the <linux/if_ether.h> include file. It defaults to the
75 socket's protocol. sll_ifindex is the interface index of the interface
76 (see netdevice(7)); 0 matches any interface (only permitted for bind‐
77 ing). sll_hatype is an ARP type as defined in the <linux/if_arp.h>
78 include file. sll_pkttype contains the packet type. Valid types are
79 PACKET_HOST for a packet addressed to the local host, PACKET_BROADCAST
80 for a physical layer broadcast packet, PACKET_MULTICAST for a packet
81 sent to a physical layer multicast address, PACKET_OTHERHOST for a
82 packet to some other host that has been caught by a device driver in
83 promiscuous mode, and PACKET_OUTGOING for a packet originated from the
84 local host that is looped back to a packet socket. These types make
85 sense only for receiving. sll_addr and sll_halen contain the physical
86 layer (e.g., IEEE 802.3) address and its length. The exact interpreta‐
87 tion depends on the device.
88 When you send packets it is enough to specify sll_family, sll_addr,
90 sll_halen, sll_ifindex. The other fields should be 0. sll_hatype and
91 sll_pkttype are set on received packets for your information. For bind
92 only sll_protocol and sll_ifindex are used.
93 Socket options
95 Packet sockets can be used to configure physical layer multicasting and
96 promiscuous mode. It works by calling setsockopt(2) on a packet socket
97 for SOL_PACKET and one of the options PACKET_ADD_MEMBERSHIP to add a
98 binding or PACKET_DROP_MEMBERSHIP to drop it. They both expect a
99 packet_mreq structure as argument:
100 struct packet_mreq {
102 int mr_ifindex; /* interface index */
103 unsigned short mr_type; /* action */
104 unsigned short mr_alen; /* address length */
105 unsigned char mr_address[8]; /* physical layer address */
106 };
107 mr_ifindex contains the interface index for the interface whose status
109 should be changed. The mr_type parameter specifies which action to
110 perform. PACKET_MR_PROMISC enables receiving all packets on a shared
111 medium (often known as "promiscuous mode"), PACKET_MR_MULTICAST binds
112 the socket to the physical layer multicast group specified in
113 mr_address and mr_alen, and PACKET_MR_ALLMULTI sets the socket up to
114 receive all multicast packets arriving at the interface.
115 In addition the traditional ioctls SIOCSIFFLAGS, SIOCADDMULTI, SIOCDEL‐
117 MULTI can be used for the same purpose.
118 Ioctls
120 SIOCGSTAMP can be used to receive the timestamp of the last received
121 packet. Argument is a struct timeval.
122 In addition all standard ioctls defined in netdevice(7) and socket(7)
124 are valid on packet sockets.
125 Error handling
127 Packet sockets do no error handling other than errors occurred while
128 passing the packet to the device driver. They don't have the concept
129 of a pending error.
130
132 EADDRNOTAVAIL
133 Unknown multicast group address passed.
134 EFAULT User passed invalid memory address.
136 EINVAL Invalid argument.
138 EMSGSIZE
140 Packet is bigger than interface MTU.
141 ENETDOWN
143 Interface is not up.
144 ENOBUFS
146 Not enough memory to allocate the packet.
147 ENODEV Unknown device name or interface index specified in interface
149 address.
150 ENOENT No packet received.
152 ENOTCONN
154 No interface address passed.
155 ENXIO Interface address contained an invalid interface index.
157 EPERM User has insufficient privileges to carry out this operation.
159 In addition other errors may be generated by the low-level
161 driver.
162
164 AF_PACKET is a new feature in Linux 2.2. Earlier Linux versions sup‐
165 ported only SOCK_PACKET.
166 The include file <netpacket/packet.h> is present since glibc 2.1.
168 Older systems need:
169 #include <asm/types.h>
171 #include <linux/if_packet.h>
172 #include <linux/if_ether.h> /* The L2 protocols */
173
175 For portable programs it is suggested to use AF_PACKET via pcap(3);
176 although this covers only a subset of the AF_PACKET features.
177 The SOCK_DGRAM packet sockets make no attempt to create or parse the
179 IEEE 802.2 LLC header for a IEEE 802.3 frame. When ETH_P_802_3 is
180 specified as protocol for sending the kernel creates the 802.3 frame
181 and fills out the length field; the user has to supply the LLC header
182 to get a fully conforming packet. Incoming 802.3 packets are not mul‐
183 tiplexed on the DSAP/SSAP protocol fields; instead they are supplied to
184 the user as protocol ETH_P_802_2 with the LLC header prepended. It is
185 thus not possible to bind to ETH_P_802_3; bind to ETH_P_802_2 instead
186 and do the protocol multiplex yourself. The default for sending is the
187 standard Ethernet DIX encapsulation with the protocol filled in.
188 Packet sockets are not subject to the input or output firewall chains.
190 Compatibility
192 In Linux 2.0, the only way to get a packet socket was by calling
193 socket(AF_INET, SOCK_PACKET, protocol). This is still supported but
194 strongly deprecated. The main difference between the two methods is
195 that SOCK_PACKET uses the old struct sockaddr_pkt to specify an inter‐
196 face, which doesn't provide physical layer independence.
197 struct sockaddr_pkt {
199 unsigned short spkt_family;
200 unsigned char spkt_device[14];
201 unsigned short spkt_protocol;
202 };
203 spkt_family contains the device type, spkt_protocol is the IEEE 802.3
205 protocol type as defined in <sys/if_ether.h> and spkt_device is the
206 device name as a null-terminated string, for example, eth0.
207 This structure is obsolete and should not be used in new code.
209
211 glibc 2.1 does not have a define for SOL_PACKET. The suggested work‐
212 around is to use:
213 #ifndef SOL_PACKET
215 #define SOL_PACKET 263
216 #endif
217 This is fixed in later glibc versions and also does not occur on libc5
219 systems.
220 The IEEE 802.2/803.3 LLC handling could be considered as a bug.
222 Socket filters are not documented.
224 The MSG_TRUNC recvmsg(2) extension is an ugly hack and should be
226 replaced by a control message. There is currently no way to get the
227 original destination address of packets via SOCK_DGRAM.
228
230 socket(2), pcap(3), capabilities(7), ip(7), raw(7), socket(7)
231 RFC 894 for the standard IP Ethernet encapsulation. RFC 1700 for the
233 IEEE 802.3 IP encapsulation.
234 The <linux/if_ether.h> include file for physical layer protocols.
236
238 This page is part of release 3.53 of the Linux man-pages project. A
239 description of the project, and information about reporting bugs, can
240 be found at http://www.kernel.org/doc/man-pages/.
241Linux 2012-05-10 PACKET(7)