FreeBSD/Linux Kernel Cross Reference
sys/net/ethernet.h

     /*
      * Fundamental constants relating to ethernet.
      *
      * $FreeBSD: src/sys/net/ethernet.h,v 1.2.2.1 1999/09/05 08:17:31 peter Exp $
      *
      */
     
     #ifndef _NET_ETHERNET_H_
     #define _NET_ETHERNET_H_
    
    /*
     * The number of bytes in an ethernet (MAC) address.
     */
    #define ETHER_ADDR_LEN          6
    
    /*
     * The number of bytes in the type field.
     */
    #define ETHER_TYPE_LEN          2
    
    /*
     * The number of bytes in the trailing CRC field.
     */
    #define ETHER_CRC_LEN           4
    
    /*
     * The length of the combined header.
     */
    #define ETHER_HDR_LEN           (ETHER_ADDR_LEN*2+ETHER_TYPE_LEN)
    
    /*
     * The minimum packet length.
     */
    #define ETHER_MIN_LEN           64
    
    /*
     * The maximum packet length.
     */
    #define ETHER_MAX_LEN           1518
    
    /*
     * A macro to validate a length with
     */
    #define ETHER_IS_VALID_LEN(foo) \
            ((foo) >= ETHER_MIN_LEN && (foo) <= ETHER_MAX_LEN)
    
    /*
     * Structure of a 10Mb/s Ethernet header.
     */
    struct  ether_header {
            u_char  ether_dhost[ETHER_ADDR_LEN];
            u_char  ether_shost[ETHER_ADDR_LEN];
            u_short ether_type;
    };
    
    /*
     * Structure of a 48-bit Ethernet address.
     */
    struct  ether_addr {
            u_char octet[ETHER_ADDR_LEN];
    };
    
    #endif

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