Question

Compare and contrast an Ethernet frame with a different layer 2 frame header. How are they different?

Compare the Cisco ISO CLI to another Cisco CLI platform. How are they similar and how are they different?

Look at an Ethernet frame and review the header. Take five items that are included in the frame header and explain their function.

Answer 1

Ethernet frame: When transmitting data over Ethernet, the Ethernet frame is primarily responsible for the correct rulemaking and successful transmission of data packets. Essentially, data sent over Ethernet is carried by the frame. An Ethernet frame is between 64 bytes and 1,518 bytes big, depending on the size of the data to be transported.

In an Ethernet network, devices share data using packets. They contain, among other things, the Ethernet frame, which is divided into several data sets. These records consist of binary code that provides important information, such as addresses, control information, payload data, and checksums.

Depending on the Ethernet standard, Ethernet frames are structured differently and may contain more or fewer data fields, depending on the network protocol.

Difference Between Frame and Packet

The crucial difference between frame and packet is that frame is the serial collection of bits, and it encapsulates packets whereas packets are the fragmented form of data and it encapsulates segment.

Data link layer performs framing process. On the other hand, Network layer performs fragmentation of the data and create smaller chunks known as packets. Another major difference is that a frame includes device’s MAC address while a packet includes device’s IP address.

BASIS FOR COMPARISON	FRAME	Packet
Basic	Frame is the data link layer protocol data unit.	Packet is the network layer protocol data unit.
Associated OSI layer	Data link layer	Network layer
Includes	Source and destination MAC address.	Source and destination IP address
Correlation	Segment is encapsulated within a packet.	Packet is encapsulated within a frame.

Q.2: Ans: Cisco ISO CLI to another Cisco CLI platform

Cisco IOS command-line interface (CLI): The Cisco IOS command-line interface (CLI) is the primary user interface used for configuring, monitoring, and maintaining Cisco devices. This user interface allows you to directly and simply execute Cisco IOS commands, whether using a router console or terminal, or using remote access methods.

Cisco CLI: Command Line Interface is a user-friendly interface. It is mostly used in network device management. Using Command Line Interface, user can easily communicate to any component in a computer, hardware device, network device, operating system, and other applications.

Advantages of CLI

Following are the advantages of the Command Line Interface:

• You can make and modify configuration settings.
• You can create, update, and delete a component, device in a network, or any database information
• You can start, stop and suspend any service in network operation.
• You can control a service running on a network device.
• You can enable and disable a switching component in a network or in any conditional storage variable.
• You can view the properties of a network device or any specified component.
• Command line Interface is either text string based or character key based. This makes the Command Line Interface very user friendly. Any terminal interface, such as Telnet interface, Serial interface, etc. acts as a CLI.

Difference between CISCO IOS and CISCO CLI

We cant compare IOS with CLI beucase IOS is like operating system or a Cisco device whereas CLI (command line interface) is a method to operate that operating system. Means that IOS is like Windows XP whereas CLI is like graphical user interface which we use to deliver instructions to our Windows operating system.

Q.3: Ans: Ethernet frame: In computer networking, an Ethernet frame is a data link layer protocol data unit and uses the underlying Ethernet physical layer transport mechanisms. In other words, a data unit on an Ethernet link transports an Ethernet frame as its payload.

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. Each Ethernet frame starts with an Ethernet header, which contains destination and source MAC addresses as its first two fields. The middle section of the frame is payload data including any headers for other protocols (for example, Internet Protocol) carried in the frame. The frame ends with a frame check sequence (FCS), which is a 32-bit cyclic redundancy check used to detect any in-transit corruption of data.

Ethernet format: An Ethernet frame contains three parts; an Ethernet header (Preamble, SFD, Destination, Source, and Type), Encapsulated data (Data and Pad), and an Ethernet trailer (FCS).

The following image shows an example of an Ethernet frame.

Ethernet header

Ethernet header contains five fields; Preamble, SFD, Destination, Source, and Type. Let's understand each field in detail.

The preamble field: The preamble field is 7 bytes long. It contains a string of 7 bytes. Each byte alternatively stores 1 and 0 to make the pattern '10101010'. Preamble bytes help the receiving device to identify the beginning of an Ethernet frame. When a device receives 7 continuous bytes of the same pattern (10101010), it assumes that the incoming data is an Ethernet frame and it locks the incoming bit-stream.

The SFD field: The SFD (Start Frame Delimiter) field is 1 byte long. It contains a string of 1 byte. This byte also stores the same pattern, except the last bit. In the last bit, it stores 1 instead of the 0. The following image shows both fields with their related bytes respectively.

The SFD byte indicates the receiving device that the next byte is the destination MAC address of the Ethernet frame.

Destination MAC address: This field is 6 bytes long. It contains the MAC address of the destination device. MAC address is 6 bytes or 48 bits (1 byte = 8 bits, 6x8 = 48bits) long. For convenience, usually, it is written as 12-digit hexadecimal numbers (such as 0000.0A12.1234).

The destination MAC address allows the receiving device to determine whether an incoming frame is intended for it or not. If a frame is not intended for the receiving device, the receiving device discards that frame.

Source MAC address: This field is also 6 bytes long. It contains the MAC address of the source device. It helps the receiving device in identifying the source device. The following image shows an example of both types of address in the frame.

Type field:

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. The Data link layer of the destination computer picks the Ethernet frame from the media. After picking the Ethernet frame, the Data link layer of the destination computer unpacks, processes, and hands over that Ethernet frame to the upper layer for further processing.

If multiple protocols are running in the upper (network) layer of the destination computer, the data link layer will fail to hand over the received frame to the upper layer as it does not know to which protocol it should give the received frame.

Data and Pad field

This field stores the encapsulated data of the upper layer. This field has a size limit of 46 bytes (minimum) to 1500 bytes (maximum). Due to this limit, the network (upper) layer can't pack more or less data in a single packet (encapsulated data of the upper layer). If data is less than the minimum requirement, padding is added. If data is more than the maximum limit, extra data is packed in the next packet.

FCS (Frame Check Sequence)

This field is 4 bytes long. This field stores a 4 bytes value that is used to check whether the received frame is intact or not. The sender device takes all fields of the frame except the FCS field, and runs them through an algorithm, known as the CRC (Cyclic Redundancy Check). The CRC algorithm generates a 4-byte result, which is placed in this FCS field.

When the destination device receives a frame, it takes the same fields and runs them through the same algorithm. If the result matches with the value stored in the FCS field, the frame is considered good and is processed further. If both values do not match, the frame is considered bad and is dropped.