1PACKET(7) Linux Programmer's Manual PACKET(7)
2
6 packet, PF_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(PF_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 PF_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 only get packets 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
62 The sockaddr_ll is a device independent physical layer address.
63 struct sockaddr_ll {
65 unsigned short sll_family; /* Always AF_PACKET */
66 unsigned short sll_protocol; /* Physical layer protocol */
67 int sll_ifindex; /* Interface number */
68 unsigned short sll_hatype; /* Header type */
69 unsigned char sll_pkttype; /* Packet type */
70 unsigned char sll_halen; /* Length of address */
71 unsigned char sll_addr[8]; /* Physical layer address */
72 };
73 sll_protocol is the standard ethernet protocol type in network order as
75 defined in the <linux/if_ether.h> include file. It defaults to the
76 socket's protocol. sll_ifindex is the interface index of the interface
77 (see netdevice(7)); 0 matches any interface (only legal for binding).
78 sll_hatype is a ARP type as defined in the <linux/if_arp.h> include
79 file. sll_pkttype contains the packet type. Valid types are
80 PACKET_HOST for a packet addressed to the local host, PACKET_BROADCAST
81 for a physical layer broadcast packet, PACKET_MULTICAST for a packet
82 sent to a physical layer multicast address, PACKET_OTHERHOST for a
83 packet to some other host that has been caught by a device driver in
84 promiscuous mode, and PACKET_OUTGOING for a packet originated from the
85 local host that is looped back to a packet socket. These types make
86 only sense for receiving. sll_addr and sll_halen contain the physical
87 layer (e.g. IEEE 802.3) address and its length. The exact interpreta‐
88 tion depends on the device.
89 When you send packets it is enough to specify sll_family, sll_addr,
91 sll_halen, sll_ifindex. The other fields should be 0. sll_hatype and
92 sll_pkttype are set on received packets for your information. For bind
93 only sll_protocol and sll_ifindex are used.
94
97 Packet sockets can be used to configure physical layer multicasting and
98 promiscuous mode. It works by calling setsockopt(2) on a packet socket
99 for SOL_PACKET and one of the options PACKET_ADD_MEMBERSHIP to add a
100 binding or PACKET_DROP_MEMBERSHIP to drop it. They both expect a
101 packet_mreq structure as argument:
102 struct packet_mreq {
104 int mr_ifindex; /* interface index */
105 unsigned short mr_type; /* action */
106 unsigned short mr_alen; /* address length */
107 unsigned char mr_address[8]; /* physical layer address */
108 };
109 mr_ifindex contains the interface index for the interface whose status
111 should be changed. The mr_type parameter specifies which action to
112 perform. PACKET_MR_PROMISC enables receiving all packets on a shared
113 medium (often known as ``promiscuous mode''), PACKET_MR_MULTICAST binds
114 the socket to the physical layer multicast group specified in
115 mr_address and mr_alen, and PACKET_MR_ALLMULTI sets the socket up to
116 receive all multicast packets arriving at the interface.
117 In addition the traditional ioctls SIOCSIFFLAGS, SIOCADDMULTI, SIOCDEL‐
119 MULTI can be used for the same purpose.
120
124 SIOCGSTAMP can be used to receive the time stamp of the last received
125 packet. Argument is a struct timeval.
126 In addition all standard ioctls defined in netdevice(7) and socket(7)
128 are valid on packet sockets.
129
132 Packet sockets do no error handling other than errors occurred while
133 passing the packet to the device driver. They don't have the concept
134 of a pending error.
135
138 In Linux 2.0, the only way to get a packet socket was by calling
139 socket(PF_INET, SOCK_PACKET, protocol). This is still supported but
140 strongly deprecated. The main difference between the two methods is
141 that SOCK_PACKET uses the old struct sockaddr_pkt to specify an inter‐
142 face, which doesn't provide physical layer independence.
143 struct sockaddr_pkt {
145 unsigned short spkt_family;
146 unsigned char spkt_device[14];
147 unsigned short spkt_protocol;
148 };
149 spkt_family contains the device type, spkt_protocol is the IEEE 802.3
151 protocol type as defined in <sys/if_ether.h> and spkt_device is the
152 device name as a null terminated string, e.g. eth0.
153 This structure is obsolete and should not be used in new code.
155
158 For portable programs it is suggested to use PF_PACKET via pcap(3);
159 although this only covers a subset of the PF_PACKET features.
160 The SOCK_DGRAM packet sockets make no attempt to create or parse the
162 IEEE 802.2 LLC header for a IEEE 802.3 frame. When ETH_P_802_3 is
163 specified as protocol for sending the kernel creates the 802.3 frame
164 and fills out the length field; the user has to supply the LLC header
165 to get a fully conforming packet. Incoming 802.3 packets are not mul‐
166 tiplexed on the DSAP/SSAP protocol fields; instead they are supplied to
167 the user as protocol ETH_P_802_2 with the LLC header prepended. It is
168 thus not possible to bind to ETH_P_802_3; bind to ETH_P_802_2 instead
169 and do the protocol multiplex yourself. The default for sending is the
170 standard Ethernet DIX encapsulation with the protocol filled in.
171 Packet sockets are not subject to the input or output firewall chains.
173
176 ENETDOWN
177 Interface is not up.
178 ENOTCONN
181 No interface address passed.
182 ENODEV Unknown device name or interface index specified in interface
185 address.
186 EMSGSIZE
189 Packet is bigger than interface MTU.
190 ENOBUFS
193 Not enough memory to allocate the packet.
194 EFAULT User passed invalid memory address.
197 EINVAL Invalid argument.
200 ENXIO Interface address contained illegal interface index.
203 EPERM User has insufficient privileges to carry out this operation.
206 EADDRNOTAVAIL
209 Unknown multicast group address passed.
210 ENOENT No packet received.
213 In addition other errors may be generated by the low-level
215 driver.
216
218 PF_PACKET is a new feature in Linux 2.2. Earlier Linux versions sup‐
219 ported only SOCK_PACKET.
220
223 glibc 2.1 does not have a define for SOL_PACKET. The suggested work‐
224 around is to use
225 #ifndef SOL_PACKET
226 #define SOL_PACKET 263
227 #endif
228 This is fixed in later glibc versions and also does not occur on libc5
229 systems.
230 The IEEE 802.2/803.3 LLC handling could be considered as a bug.
232 Socket filters are not documented.
234 The MSG_TRUNC recvmsg() extension is an ugly hack and should be
236 replaced by a control message. There is currently no way to get the
237 original destination address of packets via SOCK_DGRAM.
238
241 The include file <netpacket/packet.h> is present since glibc2.1. Older
242 systems need
243 #include <asm/types.h>
245 #include <linux/if_packet.h>
246 #include <linux/if_ether.h> /* The L2 protocols */
247
249 socket(2), pcap(3), capabilities(7), ip(7), raw(7), socket(7)
250 RFC 894 for the standard IP Ethernet encapsulation.
252 RFC 1700 for the IEEE 802.3 IP encapsulation.
254 The <linux/if_ether.h> include file for physical layer protocols.
256Linux Man Page 1999-04-29 PACKET(7)