How do I receive layer 2 packets in POSIXy C++? The packets only have src and dst MAC address, type/length, and custom formatted data. They're not TCP or UDP or IP or IGMP or ARP or whatever - they're a home-brewed format given unto me by the Hardware guys.
My socket(AF_PACKET, SOCK_RAW, IPPROTO_RAW)
never returns from its recvfrom()
.
I can send fine, I just can't receive no matter what options I fling at the network stack.
(Platform is VxWorks, but I can translate POSIX or Linux or whatever...)
receive code (current incarnation):
int s;
if ((s = socket(AF_PACKET, SOCK_RAW, IPPROTO_RAW)) < 0) {
printf("socket create error.");
return -1;
}
struct ifreq _ifr;
strncpy(_ifr.ifr_name, "lltemac0", strlen("lltemac0"));
ioctl(s, IP_SIOCGIFINDEX, &_ifr);
struct sockaddr_ll _sockAttrib;
memset(&_sockAttrib, 0, sizeof(_sockAttrib));
_sockAttrib.sll_len = sizeof(_sockAttrib);
_sockAttrib.sll_family = AF_PACKET;
_sockAttrib.sll_protocol = IFT_ETHER;
_sockAttrib.sll_ifindex = _ifr.ifr_ifindex;
_sockAttrib.sll_hatype = 0xFFFF;
_sockAttrib.sll_pkttype = PACKET_HOST;
_sockAttrib.sll_halen = 6;
_sockAttrib.sll_addr[0] = 0x00;
_sockAttrib.sll_addr[1] = 0x02;
_sockAttrib.sll_addr[2] = 0x03;
_sockAttrib.sll_addr[3] = 0x12;
_sockAttrib.sll_addr[4] = 0x34;
_sockAttrib.sll_addr[5] = 0x56;
int _sockAttribLen = sizeof(_sockAttrib);
char packet[64];
memset(packet, 0, sizeof(packet));
if (recvfrom(s, (char *)packet, sizeof(packet), 0,
(struct sockaddr *)&_sockAttrib, &_sockAttribLen) < 0)
{
printf("packet receive error.");
}
// code never reaches here
Creating a Raw Socket To create a socket of type SOCK_RAW, call the socket or WSASocket function with the af parameter (address family) set to AF_INET or AF_INET6, the type parameter set to SOCK_RAW, and the protocol parameter set to the protocol number required.
Raw packet is used when you dont have any, the first bytes captured are directly the IPv6 or IPv4 header. Raw IP; the packet begins with an IPv4 or IPv6 header, with the "version" field of the header indicating whether it's an IPv4 or IPv6 header.
A raw Ethernet packet is the complete Layer 2 network frame that is sent to the physical wire. Sending a frame like this allows you to manipulate the target and source MAC addresses and the Layer 3 protocol fields.
For example, a PING program may create a socket of type SOCK_RAW to send ICMP echo requests and receive responses. While the application is expecting ICMP echo responses, if several SOCK_RAW sockets are open on a computer at the same time, the same datagrams may be delivered to all the open sockets.
Have you tried setting the socket protocol to htons(ETH_P_ALL)
as prescribed in packet(7)
? What you're doing doesn't have much to do with IP (although IPPROTO_RAW
may be some wildcard value, dunno)
I think the way to do this is to write your own Network Service that binds to the MUX layer in the VxWorks network stack. This is reasonably well documented in the VxWorks Network Programmer's Guide and something I have done a number of times.
A custom Network Service can be configured to see all layer 2 packets received on a network interface using the MUX_PROTO_SNARF service type, which is how Wind River's own WDB protocol works, or packets with a specific protocol type.
It is also possible to add a socket interface to your custom Network Service by writing a custom socket back-end that sits between the Network Service and the socket API. This is not required if you are happy to do the application processing in the Network Service.
You haven't said which version of VxWorks you are using but I think the above holds for VxWorks 5.5.x and 6.x
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