Packet sockets allow a program to more directly interface with the networking stack than standard Layer 4 Berkeley sockets (e.g. AF_INET + SOCK_STREAM, AF_INET6 + SOCK_DGRAM).
As described in packet(7), this is a packet interface at the device level (Layer 2). The protocol field is either an IEEE 802.3 protocol number (found in linux/if_ether.h or ETH_P_ALL in network byte order. The CAP_NET_RAW capability or UID 0 are requisite to open a packet socket. bind(2) can be used to select a single interface to use with the packet socket.
Raw packets including the link-level header.
Cooked packets (common, protocol-independent link-layer header in a sockaddr_ll).
The protocol field restricts the Layer 3 protocols which will be passed to the socket; IPPROTO_RAW can set arbitrary IP protocol values, and thus implies the IP_HDRINCL socket option.
Obsolete since Linux 2.0.