open_link ~filter interface. Creates a rawlink on the specified
interface, a BPF program
filter can be passed to filter out incoming packets.
close_link. Closes a rawlink.
read_packet t. Reads a full packet, may raise Unix.Unix_error.
send_packet t. Sends a full packet, may raise Unix.Unix_error.
dhcp_server_filter. Returns a BPF program suitable to be passed in
open_link ~filter, it accepts UDP packets destined to port 67 (DHCP client).