Linux Kernel Network Programming – struct ethhdr data-structure – Introduction code walk eth_hdr() skb_mac_header()

For more details refer Linux Kernel Source:
struct ethhdr ↗
eth_hdr() API ↗
skb_mac_header() API ↗

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Linux Kernel Network stack and architecture ↗

Videos related to protocol header data-structures:
struct iphdr ↗
struct tcphdr ↗
struct udphdr ↗

And here is the copy paste of struct ethhdr data-structure (/include/uapi/linux/if_ether.h) from the Kernel-source version 4.13 for quick reference:

/*
 *	This is an Ethernet frame header.
 */

struct ethhdr {
	unsigned char	h_dest[ETH_ALEN];	/* destination eth addr	*/
	unsigned char	h_source[ETH_ALEN];	/* source ether addr	*/
	__be16		h_proto;		/* packet type ID field	*/
} __attribute__((packed));

Where these are the various Ethernet Header related constants, which are defined in the same file (/include/uapi/linux/if_ether.h) from the Kernel-source version 4.13 for quick reference:

/*
 *	IEEE 802.3 Ethernet magic constants.  The frame sizes omit the preamble
 *	and FCS/CRC (frame check sequence).
 */

#define ETH_ALEN	6		/* Octets in one ethernet addr	 */
#define ETH_HLEN	14		/* Total octets in header.	 */
#define ETH_ZLEN	60		/* Min. octets in frame sans FCS */
#define ETH_DATA_LEN	1500		/* Max. octets in payload	 */
#define ETH_FRAME_LEN	1514		/* Max. octets in frame sans FCS */
#define ETH_FCS_LEN	4		/* Octets in the FCS		 */

#define ETH_MIN_MTU	68		/* Min IPv4 MTU per RFC791	*/
#define ETH_MAX_MTU	0xFFFFU		/* 65535, same as IP_MAX_MTU	*/