ccna question format

ccna question format.As noted in Table 3.1, IEEE 802.3 is responsible for defining the framing method used to transfer information between NICs. The top half of Figure 3.1 shows the fields contained in an 802.3 frame, and Table 3.2 explains these fields.The Field Checksum Sequence (FCS) allows the target device to receive the frame and verify that it has not been tampered with.The FCS is basically a checksum that the NIC computes using an algorithm to obtain a 4-byte value based on all the fields in the 802.3 frame except for the FCS, and adds it to the FCS field. After the target device receives the frame, it performs the same algorithm on the same fields and compares the resulting 4-byte result with the FCS added to the frame by the source NIC. If these two values are different, the frame is considered invalid and is discarded. If the two values are the same, the frame is considered valid and further processing is done on it.Ethernet 802.3Encapsulated IEEE 802.2LLC framesEthernetIIEncapsulated Layer 3 packetsFigure 3.1 Ethernet frame types: Ethernet 802.3 and Ethernet II Table 3.2 Fields in an 802.3 frame2. IEEE802.2IEEE 802.2 (LLC) regulates the upper part of the data link layer. There are two types of IEEE 802.2 frames used: Service Access Point (SAP) frames and Subnet Access Protocol (SNAP) frames. When sent to the target device, these 802.2 frames are encapsulated in 802.3 frames. 802.3 (Ethernet) frames are used to transmit 802.2 frames to other devices, while 802.2 frames indicate which network layer protocol generated the data contained in their frame. In this sense, 802.2 provides multiplexing capabilities that can distinguish between data generated by TCP/IP, IPX, AppleTalk, and other network layer protocols. Figure 3.2 illustrates these two types of 802.2 frames, and Table 3.3 describes the fields of an 802.2SAP frame.When the NIC of the target device receives an 802.3 frame, it first checks the FCS to verify that the frame is valid, and then checks the destination MAC address in the 802.3 frame to determine whether to process it or ignore it. the MAC sublayer strips the 802.3 frame information and hands the 802.2 frame to the LLC sublayer. the LLC looks at the SAP value to determine which upper-layer protocol should be given the encapsulated data. Here are some possible SAP values: TCP/IP uses 0x06 (hex), while IPX uses OxOEo If the LLC finds a value of 0x06 in the SAP field, it will give the encapsulated data to the TCP/IP stack running in the device.