When stations transmit to each other on a LAN, they format the data in a structured manner so that devices know what octets signify what information. Various frame formats are available. When you configure a device, you must define what format your station will use, realizing that more than one format might be configured, as is true for a router.
Figure 1-2 illustrates four common frame formats for Ethernet. Some users interchange the terms packets and frames rather loosely. According to RFC 1122, a subtle difference exists. Frames refer to the entire message, from the data link layer (Layer 2) header information through and including the user data. Packets exclude Layer 2 headers and only include the IP header (Layer 3 protocol header) through and including user data.
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