CCNA Cisco Certified Network Associate Study Guide - FTP Server

FIGURE 1.11 802.3 and Ethernet frame formats
Preamble
8 bytes
Preamble
8 bytes
DA
6 bytes
DA
6 bytes
SA
6 bytes
Ethernet_II
SA
6 bytes
Type
2 bytes
802.3_Ethernet
Length
2 bytes
Ethernet Networking 25
Data FCS
Destination Address (DA) This transmits a 48-bit value using the Least
Significant Bit (LSB) first. DA is used by receiving stations to determine if
an incoming packet is addressed to a particular node. The destination
address can be an individual address, or a broadcast or multicast
MAC address. Remember that a broadcast is all 1s or Fs in hex and is sent
to all devices, whereas a multicast is sent to only a similar subset of nodes
on a network.
Hex is short for hexadecimal, which is a numbering system that uses the first
six letters of the alphabet (A through F) to extend beyond the available 10 digits
in the decimal system. Hexadecimal has a total of 16 digits.
Source Address (SA) SA is a 48-bit MAC address supplied by the transmitting
device. It uses the Least Significant Bit (LSB) first. Broadcast and
multicast address formats are illegal within the SA field.
Length or Type field 802.3 uses a length field, whereas the Ethernet
frame uses a type field to identify the Network layer protocol. 802.3 cannot
identify the upper-layer protocol and must be used with a proprietary
LAN, for example, IPX.
Data
FCS
4 bytes