The primary fields in the Ethernet frame are: Show
Ethernet FrameSummary This topic explain how the Ethernet sublayers are related to the frame fields. Start learning CCNA 200-301 for free right now!! Note: Welcome: This topic is part of Chapter 7 of the Cisco CCNA 1 course, for a better follow up of the course you can go to the CCNA 1 section to guide you through an order.
Ethernet EncapsulationThis module starts with a discussion of Ethernet technology including an explanation of MAC sublayer and the Ethernet frame fields. Ethernet is one of two LAN technologies used today, with the other being wireless LANs (WLANs). Ethernet uses wired communications, including twisted pair, fiber-optic links, and coaxial cables. Ethernet operates in the data link layer and the physical layer. It is a family of networking technologies defined in the IEEE 802.2 and 802.3 standards. Ethernet supports data bandwidths of the following:
As shown in the figure, Ethernet standards define both the Layer 2 protocols and the Layer 1 technologies. Ethernet and the OSI ModelEthernet and the OSI ModelEthernet is defined by data link layer and physical layer protocols. Data Link SublayersIEEE 802 LAN/MAN protocols, including Ethernet, use the following two separate sublayers of the data link layer to operate. They are the Logical Link Control (LLC) and the Media Access Control (MAC), as shown in the figure. Recall that LLC and MAC have the following roles in the data link layer:
MAC SublayerThe MAC sublayer is responsible for data encapsulation and accessing the media. Data Encapsulation IEEE 802.3 data encapsulation includes the following:
Accessing the Media As shown in the figure, the IEEE 802.3 MAC sublayer includes the specifications for different Ethernet communications standards over various types of media including copper and fiber. Ethernet Standards in the MAC SublayerEthernet Standards in the MAC SublayerRecall that legacy Ethernet using a bus topology or hubs, is a shared, half-duplex medium. Ethernet over a half-duplex medium uses a contention-based access method, carrier sense multiple access/collision detection (CSMA/CD) This ensures that only one device is transmitting at a time. CSMA/CD allows multiple devices to share the same half-duplex medium, detecting a collision when more than one device attempts to transmit simultaneously. It also provides a back-off algorithm for retransmission. Ethernet LANs of today use switches that operate in full-duplex. Full-duplex communications with Ethernet switches do not require access control through CSMA/CD. Ethernet Frame FieldsThe minimum Ethernet frame size is 64 bytes and the maximum is 1518 bytes. This includes all bytes from the destination MAC address field through the frame check sequence (FCS) field. The preamble field is not included when describing the size of the frame. Any frame less than 64 bytes in length is considered a “collision fragment” or “runt frame” and is automatically discarded by receiving stations. Frames with more than 1500 bytes of data are considered “jumbo” or “baby giant frames”. If the size of a transmitted frame is less than the minimum, or greater than the maximum, the receiving device drops the frame. Dropped frames are likely to be the result of collisions or other unwanted signals. They are considered invalid. Jumbo frames are usually supported by most Fast Ethernet and Gigabit Ethernet switches and NICs. The figure shows each field in the Ethernet frame. Refer to the table for more information about the function of each field. Ethernet Frame FieldsEthernet Frame FieldsEthernet Frame Fields Detail
Lab – Use Wireshark to Examine Ethernet FramesIn this lab, you will complete the following objectives:
Ready to go! Keep visiting our networking course blog, give Like to our fanpage; and you will find more tools and concepts that will make you a networking professional. Which Ethernet frame field describes the higher layer protocol that is encapsulated?Ethernet II framing (also known as DIX Ethernet, named after DEC, Intel and Xerox, the major participants in its design), defines the two-octet EtherType field in an Ethernet frame, preceded by destination and source MAC addresses, that identifies an upper layer protocol encapsulated by the frame data.
What is encapsulated into the data field of an Ethernet frame?An ARP packet is directly encapsulated (bypassing IP datagram) into an Ethernet frame, as shown in Fig.
Which section in an Ethernet frame contains data from higher layers?The data payload of a traditional Ethernet frame can be anywhere from 46 to 1500 bytes long. This contains all of the data from higher layers such as the IP, transport and application layers that's actually being transmitted.
What is Ethernet encapsulation?Ethernet encapsulation describes the process by which an 802.11 MPDU wraps a full Ethernet frame for transmission while Ethernet de-encapsulation describes the reverse.
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