Title: eth_hdr_t

An ethernet header is fairly simple. The eth_hdr_t typedef is declared in server/ip/gen/eth_hdr.h:

typedef struct eth_hdr

ether_addr_t eh_dst;
ether_addr_t eh_src;
ether_type_t eh_proto;
} eth_hdr_t;
ether_addr_t eh_dst: The destination ethernet address.

ether_addr_t eh_src: The source ethernet address.

ether_type_t eh_proto: The protocol of the layer above. The three possibilities are:

#define ETH_RARP_PROTO 0x8035
#define ETH_ARP_PROTO 0x806
#define ETH_IP_PROTO 0x800

An ethernet frame also has a CRC (Cyclic Redundancy Check) at its end to enable the receiving system to determine if corruption occured during transit.

An ethernet MAC (physical) address is a 48 bit number. This number is broken down into two halves: 22 of the first 24-bits identify the vendor of the Ethernet board (called the "Organizationally Unique Identifier") and the second 24-bits form a serial number assigned by the vendor. This guarantees that no two Ethernet cards have the same MAC address. One of the remaining bits indicate if the packet is a multicast or broadcast packet and the other is used for vendor-specific applications (e.g., NetBEUI).

| destination MAC |
| source MAC |
|08 00|
| |
. IP .
. packet .
. .
| |
| CRC |