For a more detailed discussion of this, which mentions a third possibility used by NetWare, and mentions the SNAP header that can follow the 802.2 header, see Ethernet Frame Types: Provan's Definitive Answer, by Don Provan. (XXX - we should mentioned that the 802.2/802.3 terminology used by Netware at that time is simply confusing)
Jan 28, 2020 · Both frame types have the same fields except for the 2-byte EtherType field of Ethernet II which is different from the Length field of IEEE 802.3. The Ethernet II and IEEE 802.3 aren’t compatible and won’t work with each other if both frame types are used in a LAN network. So simply, every time your computer receives an Ethernet frame, it looks at the 2-byte-long header field right after the Source MAC. If the value in this field is 1500 or less, this is a 802.2 LLC or SNAP frame, and the field is to be interpreted as Length. To distinguish the style of Ethernet header, the Ethernet Type field values begin at 1536, and the length of the Data field in an IEEE frame is limited to decimal 1500 or less. That way, an Ethernet NIC can easily determine whether the frame follows the DIX or original IEEE format. Jan 27, 2019 · The frame composition is dependent on the media access type. For example, if the upper layer protocols are TCP and IP and the media access is Ethernet, then the Layer 2 frame encapsulation will be Ethernet II. This is typical for a LAN environment. When learning about Layer 2 concepts, it is helpful to analyze frame header information. The ability to migrate the original implementation of Ethernet to current and future Ethernet implementations is based on the practically unchanged structure of the Layer 2 frame. Physical media, media access, and media control have all evolved and continue to do so. But the Ethernet frame header and trailer have essentially remained constant.
An Ethernet frame is preceded by a preamble and start frame delimiter (SFD), which are both part of the Ethernet packet at the physical layer. In the below image, focus on the IEEE 802.3 (Revised 1997) depiction of an Ethernet Frame; Ethernet Frame Diagram . Preamble. 7 bytes; Alternating 1s and 0s to make it easy for devices to synchronize
802.3 uses a Length field, but the Ethernet_2 frame uses a Type field to identify the Network layer protocol. The old, original 802.3 cannot identify the upper-layer protocol and must be used with a proprietary LAN--IPX, for example. Introduction 3 Figure 1.2: Protocol overhead in the OSI model 1.2 LAN A local network (Local Area Network (LAN)) has been developed to ensure communication between computers, work stations and peripherals in an area of a very limited geographical Ethernet frame types include Ethernet 802.3, Ethernet 802.2, Ethernet II, and Ethernet SNAP. When two systems need to communicate on an Ethernet network, they must be using a common frame format. The confusion as to when a given Ethernet frame type is used is generally a result of different vendors and standards bodies moving in different AmazonBasics RJ45 Cat-5e Network Ethernet Cable - 50 Feet (15.2 Meters) 4.6 out of 5 stars 6,830. $10.49 $ 10. 49. TBMax Cat6 Ethernet Cable Flat 50ft - Cat 6 Network
The Ethernet frame defines the data layout at the OSI Layer 2 link level. The length of an Ethernet frame is normally no less than 64 octets and no more than 1,518 octets. The exception to the minimum length is the gigabit Ethernet standard 802.3z, which increased the minimum packet size to 512 bytes.
The ability to migrate the original implementation of Ethernet to current and future Ethernet implementations is based on the practically unchanged structure of the Layer 2 frame. Physical media, media access, and media control have all evolved and continue to do so. But the Ethernet frame header and trailer have essentially remained constant. This field is 2 bytes long. This field stores information about the protocol of the upper layer (network layer). The Data Link layer of the source computer prepares, packs and loads the Ethernet frame in the media. Ethernet SNAP. Organization Code and Ethertype fields follow the LLC fields. Organization Code. 3 bytes. Which organization assigned the Ethernet Type field. EtherType. 2 bytes. Defines which upper layer protocol will utilize the Ethernet frame.