Create a layer 2 / ethernet socket with boost asio raw socket (in C++)

Question

It is fairly easy to create IP, TCP or UDP sockets using boost::asio library. But when it comes to Ethernet sockets for instance, you need to implement boost/asio/basic_raw_socket.hpp

As there are no examples of such a thing over the internet and as I spent a long time before finding the answer, I'll put my work-around in here.

The most helpful resource I found was: AF_NETLINK (netlink) sockets using boost::asio

Answer 1

A raw socket can be opened using the generic::raw_protocol stuff:

std::string ifname("eth1");

typedef boost::asio::generic::raw_protocol raw_protocol_t;
typedef boost::asio::generic::basic_endpoint<raw_protocol_t> raw_endpoint_t;

sockaddr_ll sockaddr;
memset(&sockaddr, 0, sizeof(sockaddr));
sockaddr.sll_family = PF_PACKET;
sockaddr.sll_protocol = htons(ETH_P_ALL);
sockaddr.sll_ifindex = if_nametoindex(ifname.c_str());
sockaddr.sll_hatype = 1;

raw_protocol_t::socket socket(io_service, raw_protocol_t(PF_PACKET, SOCK_RAW))
socket.bind(raw_endpoint_t(&sockaddr, sizeof(sockaddr)));

Answer 2

First thing to do is to create an ethernet protocol based on the basic_raw_socket class. You can modify the protocol (htons(ETH_P_ALL)) and the family (PF_PACKET) fields, depending on the traffic you want to send/receive.

/// Create a link-layer protocol associated with a link-layer endpoint
class ll_protocol
{
public:
    /// Obtain an identifier for the type of the protocol.
    int type() const
    {
        return SOCK_RAW;
    }

    /// Obtain an identifier for the protocol.
    int protocol() const
    {
        return protocol_;
    }

    /// Obtain an identifier for the protocol family.
    int family() const
    {
        return family_;
    }

    // Construct with a specific family.
    explicit ll_protocol(int protocol, int family) :
            protocol_(protocol), family_(family)
    {
    }
    explicit ll_protocol() :
            protocol_(htons(ETH_P_ALL)), family_(PF_PACKET)
    {
    }

    typedef boost::asio::basic_raw_socket<ll_protocol> socket;
    typedef ll_endpoint<ll_protocol> endpoint;

private:
    int protocol_;
    int family_;
};

To bind the socket to the interface, an endpoint is required. The key point is to create a sockaddr_ll structure, in which the interface to send/receive traffic can be specified.

#include <net/ethernet.h>
#include <sys/socket.h>
#include <linux/if_packet.h>
#include <cstddef>

template <typename Protocol>
class ll_endpoint
{
private:
    sockaddr_ll sockaddr;
public:
    /// The protocol type associated with the endpoint.
    typedef Protocol protocol_type;
    typedef boost::asio::detail::socket_addr_type data_type;

    /// Constructor
    ll_endpoint(const char* ifname)
    {
        sockaddr.sll_family = PF_PACKET;
        sockaddr.sll_protocol = htons(ETH_P_ALL);
        sockaddr.sll_ifindex = if_nametoindex(ifname);
        sockaddr.sll_hatype = 1;
    }

    /// Assign from another endpoint.
    ll_endpoint& operator=(const ll_endpoint& other)
    {
        sockaddr = other.sockaddr;
        return *this;
    }

    /// The protocol associated with the endpoint.
    protocol_type protocol() const
    {
        return protocol_type();
    }

    /// Get the underlying endpoint in the native type.
    data_type* data()
    {
        return &sockaddr;
    }

    /// Get the underlying endpoint in the native type.
    const data_type* data() const
    {
        return (struct sockaddr*)&sockaddr;
    }

    /// Get the underlying size of the endpoint in the native type.
    std::size_t size() const
    {
        return sizeof(sockaddr);
    }

    /// Set the underlying size of the endpoint in the native type.
    void resize(std::size_t size)
    {
    /* nothing we can do here */
    }

    /// Get the capacity of the endpoint in the native type.
    std::size_t capacity() const
    {
        return sizeof(sockaddr);
    }

    /// Compare two endpoints for equality.
    friend bool operator==(const ll_endpoint<Protocol>& e1,
               const ll_endpoint<Protocol>& e2)
    {
        return e1.sockaddr == e2.sockaddr;
    }

    /// Compare two endpoints for inequality.
    friend bool operator!=(const ll_endpoint<Protocol>& e1,
               const ll_endpoint<Protocol>& e2)
    {
        return !(e1.sockaddr == e2.sockaddr);
    }

    /// Compare endpoints for ordering.
    friend bool operator<(const ll_endpoint<Protocol>& e1,
              const ll_endpoint<Protocol>& e2)
    {
        return e1.sockaddr < e2.sockaddr;
    }

    /// Compare endpoints for ordering.
    friend bool operator>(const ll_endpoint<Protocol>& e1,
              const ll_endpoint<Protocol>& e2)
    {
        return e2.sockaddr < e1.sockaddr;
    }

    /// Compare endpoints for ordering.
    friend bool operator<=(const ll_endpoint<Protocol>& e1,
               const ll_endpoint<Protocol>& e2)
    {
        return !(e2 < e1);
    }

    /// Compare endpoints for ordering.
    friend bool operator>=(const ll_endpoint<Protocol>& e1,
               const ll_endpoint<Protocol>& e2)
    {
        return !(e1 < e2);
    }
};

Finally, you can open the socket and connect to the endpoint as follow:

string ifname("eth1");
ll_protocol::socket socket;
socket.open(ll_protocol());
socket.bind(ll_endpoint<ll_protocol>((const char*)ifname.c_str()));