Questions 3

What is ARP used for?

*ARP* is a communication protocol and is used to discover link layer addresses associated with a given IPv4 address.

Data Encapsulation Process

1. The upper-layer user data is converted for transmission on the network 2. The data stream is then handed down to the Transport layer, which sets up a virtual circuit to the receiving device by sending over a synch packet 3. Next, the data stream is broken up into smaller pieces, and a Transport layer header is created and attached to the header of the data field - The piece of data is called a segment (a PDU); Each segment can be sequenced so the data stream can be put back together on the receiving side exactly as it was transmitted 4. Each segment is then handed to the Network layer for network addressing and routing through the internetwork - Logical addressing (for example, IP and IPv6) is used to get each segment to the correct network; The Network layer protocol adds a control header to the segment handed down from the Transport layer, and what we have now is called a packet or datagram *The Transport and Network layers work together to rebuild a data stream on a receiving host; the Data Link layer that's responsible for taking packets from the Network layer and placing them on the network medium (cable or wireless)* 5. The Data Link layer encapsulates each packet in a frame, and the frame's header carries the hardware addresses of the source and destination hosts - If the destination device is on a remote network, then the frame is sent to a router to be routed through an internetwork; Once it gets to the destination network, a new frame is used to get the packet to the destination host - To put this frame on the network, it must first be put into a digital signal 6. Since a frame is really a logical group of 1s and 0s, the physical layer is responsible for encoding these digits into a digital signal, which is read by devices on the same local network; The receiving devices will synchronize on the digital signal and extract (decode) the 1s and 0s from the digital signal

Destination MAC Address Field

6-byte field is the identifier for the intended recipient. As you will recall, this address is used by Layer 2 to assist devices in determining if a frame is addressed to them. The address in the frame is compared to the MAC address in the device. If there is a match, the device accepts the frame. this can be unicvast, broadcast or multicast address.

Broadcast MAC Address

A MAC address in which all bits are set to 1 (FF:FF:FF:FF:FF:FF). A broadcast packet contains a destination IPv4 address that has all ones (1s) in the host portion. This numbering in the address means that all hosts on that local network (broadcast domain) will receive and process the packet. Many network protocols, such as DHCP and ARP, use broadcasts. the source host sends an IPv4 broadcast packet to all devices on its network. The IPv4 destination address is a broadcast address, 192.168.1.255. When the IPv4 broadcast packet is encapsulated in the Ethernet frame, the destination MAC address is the broadcast MAC address of FF-FF-FF-FF-FF-FF in hexadecimal (48 ones in binary).

What is contained in the FCS field of an Ethernet frame?

A frame check sequence (FCS) refers to an error-detecting code added to a frame in a communications protocol. Frames are used to send payload data from a source to a destination.

What is a destination MAC address?

A media access control address (MAC address) of a device is a unique identifier assigned to a network interface controller (NIC) for communications at the data link layer of a network segment. MAC addresses are used as a network address for most IEEE 802 network technologies, including Ethernet, Wi-Fi and Bluetooth.

What is an Ethernet MAC address?

A media access control address (MAC address) of a device is a unique identifier assigned to a network interface controller (NIC). For communications within a network segment, it is used as a network address for most IEEE 802 network technologies, including Ethernet, Wi-Fi, and Bluetooth.

What is Mac technique?

A network of computers based on multi-access medium requires a protocol for effective sharing of the media. ... The protocols used for this purpose are known as Medium Access Control (MAC) techniques.

ARP Role in Remote Communication

ARP Role in Remote Communication. All frames must be delivered to a node on the local network segment. ... In the event that the gateway entry is not in the table, the normal ARP process will send an ARP request to retrieve the MAC address associated with the IP address of the router interface.

What layer is ARP?

ARP is layer 2. The reason being is that a broadcast is sent on layer 2 (data link layer) and ARP will normally not traverse to layer 3 (network layer). However it can provide extra features to the layer 3 protocol. The truth is that not all protocols fit the OSI model exactly, because after all it's just a model

What does ARP poisoning do?

ARP spoofing is a type of attack in which a malicious actor sends falsified ARP (Address Resolution Protocol) messages over a local area network. This results in the linking of an attacker's MAC address with the IP address of a legitimate computer or server on the network.

What does ARP spoofing mean?

ARP spoofing is a type of attack in which a malicious actor sends falsified ARP (Address Resolution Protocol) messages over a local area network. This results in the linking of an attacker's MAC address with the IP address of a legitimate computer or server on the network.

How does ARP spoofing work?

ARP spoofing, ARP cache poisoning, or ARP poison routing, is a technique by which an attacker sends (spoofed) Address Resolution Protocol (ARP) messages onto a local area network. ... ARP spoofing may allow an attacker to intercept data frames on a network, modify the traffic, or stop all traffic.

What is meant by ARP poisoning?

Address Resolution Protocol poisoning (ARP poisoning) is a form of attack in which an attacker changes the Media Access Control (MAC) address and attacks an Ethernet LAN by changing the target computer's ARP cache with a forged ARP request and reply packets.

Are LAN and Ethernet the same?

Alternatively referred to as an Ethernet port, network connection, and network port, the LAN port allows a computer to connect to a network using a wired connection. The picture is a close up of what a LAN port looks like for a network cable using a RJ-45 connector. ... LAN - Ethernet - RJ-45 are one and the same port.

MAC Address and Hexadecimal

An Ethernet MAC address is a 48-bit binary value expressed as 12 hexadecimal digits (4 bits per hexadecimal digit). Just as decimal is a base ten number system, hexadecimal is a base sixteen system. The base sixteen number system uses the numbers 0 to 9 and the letters A to F. Figure 1 shows the equivalent decimal and hexadecimal values for binary 0000 to 1111. It is easier to express a value as a single hexadecimal digit than as four binary bits. Given that 8 bits (one byte) is a common binary grouping, binary 00000000 to 11111111 can be represented in hexadecimal as the range 00 to FF, as shown in Figure 2. Leading zeroes are always displayed to complete the 8-bit representation. For example, the binary value 0000 1010 is shown in hexadecimal as 0A. Note: It is important to distinguish hexadecimal values from decimal values regarding the characters 0 to 9, as shown in the figure. Representing Hexadecimal Values Hexadecimal is usually represented in text by the value preceded by 0x (for example 0x73) or a subscript 16. Less commonly, it may be followed by an H(for example 73H). However, because subscript text is not recognized in command line or programming environments, the technical representation of hexadecimal is preceded with "0x" (zero X). Therefore, the examples above would be shown as 0x0A and 0x73 respectively. Hexadecimal is used to represent Ethernet MAC addresses and IP Version 6 addresses. Hexadecimal Conversions Number conversions between decimal and hexadecimal values are straightforward, but quickly dividing or multiplying by 16 is not always convenient. If such conversions are required, it is usually easier to convert the decimal or hexadecimal value to binary, and then to convert the binary value to either decimal or hexadecimal as appropriate.

ARP Broadcasts

As a broadcast frame, an ARP request is received and processed by every device on the local network. On a typical business network, these broadcasts would probably have minimal impact on network performance. However, if a large number of devices were to be powered up and all start accessing network services at the same time, there could be some reduction in performance for a short period of time, as shown in the figure. After the devices send out the initial ARP broadcasts and have learned the necessary MAC addresses, any impact on the network will be minimized.

Filtering Frames

As a switch receives frames from different devices, it is able to populate its MAC address table by examining the source MAC address of every frame. When the switch's MAC address table contains the destination MAC address, it is able to filter the frame and forward out a single port.

What does no MDIX auto mean?

Auto-MDIX on an Interface. ... When connecting switches without the auto-MDIX feature, you must use straight-through cables to connect to devices such as servers, workstations, or routers and crossover cables to connect to other switches or repeaters.

Is Ethernet faster than WIFI?

Because Ethernet uses cables, it tends to work slightly faster than a wireless connection. Wireless connections are a bit slower, but provide the convenience of using it within range.

How do I change a port to a full duplex?

Complete these steps: Connect the two switches together. ... Examine the capabilities of the ports. ... Configure auto-negotiation for port 1/1 on both switches. ... Determine if the speed and duplex mode are set to auto-negotiate. ... Change the speed on port 1/1 in switch A to 10 Mb.

What is data encapsulation in OSI model?

Data encapsulation in the OSI model. In the previous lesson we have learned that the term encapsulation describes the process of putting headers (and sometimes trailers) around some data. ... For example, the term Layer 3 PDU refers to the data encapsulated at the Network layer of the OSI model.

Data Encapsulation

Data encapsulation provides three primary functions: Frame delimiting - The framing process provides important delimiters that are used to identify a group of bits that make up a frame. These delimiting bits provide synchronization between the transmitting and receiving nodes. Addressing - The encapsulation process contains the Layer 3 PDU and also provides for data link layer addressing. Error detection - Each frame contains a trailer used to detect any errors in transmissions. The use of frames aids in the transmission of bits as they are placed on the media and in the grouping of bits at the receiving node.

The LLC sublayer is part of which OSI model layer?

Data link

MAC sublayer responsibilities

Ethernet MAC sublayer has two primary responsibilities: Data encapsulation Media access control

Why is Ethernet important?

Ethernet Network - The Role of Ethernet in Computer Networks. An ethernet network is a situation in which multiple computers are connected to one another and share the same Internet protocol address. ... The benefit in this is that multiple networks do not need to be created.

What is Ethernet in simple terms?

Ethernet is a way of connecting computers together in a local area network or LAN. It has been the most widely used method of linking computers together in LANs since the 1990s. The basic idea of its design is that multiple computers have access to it and can send data at any time.

Ethernet Encapsulation

Ethernet is the most widely used LAN technology today. Ethernet operates in the data link layer and the physical layer. It is a family of networking technologies that are defined in the IEEE 802.2 and 802.3 standards. Ethernet supports data bandwidths of: 10 Mb/s 100 Mb/s 1000 Mb/s (1 Gb/s) 10,000 Mb/s (10 Gb/s) 40,000 Mb/s (40 Gb/s) 100,000 Mb/s (100 Gb/s) Ethernet standards define both the Layer 2 protocols and the Layer 1 technologies. For the Layer 2 protocols, as with all 802 IEEE standards, Ethernet relies on the two separate sublayers of the data link layer to operate, the Logical Link Control (LLC) and the MAC sublayers. LLC sublayer

Why was the Ethernet protocol originally developed?

Ethernet was developed at Xerox PARC between 1973 and 1974. It was inspired by ALOHAnet, which Robert Metcalfe had studied as part of his PhD dissertation. ... The first standard was published on September 30, 1980 as "The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications".

What is a FCS error?

FCS stands for Frame Check Sequence. Each ppp packet has a checksum attached to ensure that the data being received is the data being sent. If the FCS of an incoming packet is incorrect, the packet is dropped and the HDLC FCS count is increased.

How do I find my destination IP address?

Find the IP Address of a Website Using Command Prompt Step 1: Find the IP Address. Open command prompt and type in "tracert" then type in the website for example "tracert www.instructables.com" without these things"". ... Step 2: Tracing the IP Address. ... 62 Discussions.

How does ARP work in Layer 3?

For me ARP is a service protocol that glues together layer 2 and layer 3 protocols. It solves the problem that you need to add a layer 2 (MAC) destination address over a shared media like Ethernet or Wireless LAN using IP packets. But ARP is a separate process with separate packets.

Ethernet Frame Fields

Frame Check Sequence Detects errors in an Ethernet frame Start of Frame Delimiter Synchronizes sending and receiving devices for frame delivery Preamble Notifies destination to get ready for a new frame Destination Address Assists a host in determining if the frame received is addressed to it Source Address The frame's originating NIC or interface MAC address Type Describes which higher-layer protocol has been used 802.2 Header and Data Uses Pad to increase this frame field to at least 64 bytes

What is duplex settings in networking?

Full-duplex data transmission means that data can be transmitted in both directions on a signal carrier at the same time. For example, on a local area network with a technology that has full-duplex transmission, one workstation can be sending data on the line while another workstation is receiving data.

MAC and LLC Sublayers

Hacker Characteristics LLC Sublayers Controls the network interface cars though software drivers. Works with the upper layers to add application information for delivery of data to higher level protocols. Remains relatively independent of physical equipment Mac sublayers Works with hardware to support bandwidth requirements and checks errors in the bits sent and received. Controls access to the media though signalling and physical media standards requirements. Supports Ethernet technology by using CSMA/CD or CSMA/CA

How does an ARP request work?

If the IP address is not found in the ARP table, the system will then send a broadcast packet to the network using the ARP protocol to ask "who has 192.168.1.1". Because it is a broadcast packet, it is sent to a special MAC address that causes all machines on the network to receive it.

Where did Ethernet come from?

In 1973, Metcalfe changed the name to "Ethernet." He did this to make it clear that the system he had created would support any computer, not just Alto's. He chose the name based on the word "ether" as a way of describing an essential feature of the system: the physical medium carrying bits to stations.

What is duplex mismatch Cisco?

In Ethernet, a duplex mismatch is a condition where two connected devices operate in different duplex modes, that is, one operates in half duplex while the other one operates in full duplex. The effect of a duplex mismatch is a network that works but is often much slower than its nominal speed.

MAC Address: Ethernet Identity

In Ethernet, every network device is connected to the same, shared media. Ethernet was once predominantly a half-duplex topology using a multi-access bus or later Ethernet hubs. This meant that all nodes would receive every frame transmitted. To prevent the excessive overhead involved in the processing of every frame, MAC addresses were created to identify the actual source and destination. MAC addressing provides a method for device identification at the lower level of the OSI model. Although Ethernet has now transitioned to full-duplex NICs and switches, it is still possible that a device that is not the intended destination will receive an Ethernet frame. MAC Address Structure The MAC address value is a direct result of IEEE-enforced rules for vendors to ensure globally unique addresses for each Ethernet device. The rules established by IEEE require any vendor that sells Ethernet devices to register with IEEE. The IEEE assigns the vendor a 3-byte (24-bit) code, called the Organizationally Unique Identifier (OUI). IEEE requires a vendor to follow two simple rules, as shown in the figure: All MAC addresses assigned to a NIC or other Ethernet device must use that vendor's assigned OUI as the first 3 bytes. All MAC addresses with the same OUI must be assigned a unique value in the last 3 bytes. Note: It is possible for duplicate MAC addresses to exist due to mistakes during manufacturing or in some virtual machine implementation methods. In either case, it will be necessary to modify the MAC address with a new NIC or in software.

What is medium access sublayer?

In IEEE 802 LAN/MAN standards, the medium access control (MAC) sublayer (also known as the media access control sublayer) and the logical link control (LLC) sublayer together make up the data link layer. ... These two sublayers together correspond to layer 2 of the OSI model.

What is ARP broadcast?

In an Ethernet local area network, however, addresses for attached devices are 48 bits long. (The physical machine address is also known as a Media Access Control or MAC address.) A table, usually called the ARP cache, is used to maintain a correlation between each MAC address and its corresponding IP address.

What is the role of MAC protocol?

In telecommunication protocols, MAC addresses are used by the Media Access Control sub-layer of the Data Link Control (DLC) layer, which is the protocol layer of a program that handles the flow of data moving in and out over physical links in the network.

What is the basic purpose of MAC layer protocol?

In the Open Systems Interconnection (OSI) model of communication, the Media Access Control layer is one of two sublayers of the Data Link Control layer and is concerned with sharing the physical connection to the network among several computers. Each computer has its own unique MAC address.

What is LLC and MAC in data link layer?

LLC layer is also known as the logical link control. As it is evident from the name itself that for the data link layer, the LLC layer serves the purpose of providing end to end flow, error control, and multiplexing different protocols over the Mac layer of the data link layer.

What are the functions of MAC layer?

MAC Layer - Media Access Control Layer. The Media Access Control Layer is one of two sublayers that make up the Data Link Layer of the OSI model. The MAC layer is responsible for moving data packets to and from one Network Interface Card (NIC) to another across a shared channel.

MAC sublayer

MAC constitutes the lower sublayer of the data link layer. MAC is implemented by hardware, typically in the computer NIC. The specifics are listed in the IEEE 802.3 standards.

What causes CRC errors on Ethernet?

MAC frame CRC errors can be caused by a number of factors. Typically they are caused by either faulty cabling, or as the result of a collision. If the cabling connecting an Ethernet Adapter or hub is faulty the electric connection may be on and off many times during a transmission.

What is source and destination?

Many computer commands involve moving data. The place from which the data is moved is called the source, whereas the place it is moved to is called the destination or target. If you copy a file from one directory to another, for example, you copy it from the source directory to the destination directory.

What is media access control layer?

Media access control (MAC) is a sublayer of the data link layer (DLL) in the seven-layer OSI network reference model. MAC is responsible for the transmission of data packets to and from the network-interface card, and to and from another remotely shared channel.

ARP spoofing

More commonly known as ARP poisoning, this involves the MAC (Media Access Control) address of the data being faked. In some cases, the use of ARP can lead to a potential security risk known as ARP spoofing or ARP poisoning. This is a technique used by an attacker to reply to an ARP request for an IPv4 address belonging to another device, such as the default gateway, as shown in the figure. The attacker sends an ARP reply with its own MAC address. The receiver of the ARP reply will add the wrong MAC address to its ARP table and send these packets to the attacker. Enterprise level switches include mitigation techniques known as dynamic ARP inspection (DAI).

Multicast MAC Address

Multicast addresses allow a source device to send a packet to a group of devices. Devices that belong to a multicast group are assigned a multicast group IP address. The range of IPv4 multicast addresses is 224.0.0.0 to 239.255.255.255. The range of IPv6 multicast addresses begin with FF00::/8. Because multicast addresses represent a group of addresses (sometimes called a host group), they can only be used as the destination of a packet. The source will always be a unicast address. Multicast addresses would be used in remote gaming, where many players are connected remotely but playing the same game. Another use of multicast addresses is in distance learning through video conferencing, where many students are connected to the same class. As with the unicast and broadcast addresses, the multicast IP address requires a corresponding multicast MAC address to actually deliver frames on a local network. The multicast MAC address associated with an IPv4 multicast address is a special value that begins with 01-00-5E in hexadecimal. The remaining portion of the multicast MAC address is created by converting the lower 23 bits of the IP multicast group address into 6 hexadecimal characters. For an IPv6 address, the multicast MAC address begins with 33-33.

How many bytes is an Ethernet frame?

Note - Size of frame of Ethernet IEEE 802.3 varies 64 bytes to 1518 bytes including data length (46 to 1500 bytes)

ARP Tables

On a Cisco router, the show ip arp command is used to display the ARP table. On a Windows 7 PC, the arp -a command is used to display the ARP table.

What is duplex speed?

Per the IEEE specification, gigabit speed is available only in full-duplex. The settings available when auto-negotiation is disabled are: 10 Mbps or 100 Mbps Full duplex (requires a full duplex capable link partner set to full duplex). The adapter can send and receive packets at the same time.

what are the ARP Functions?

Resolving IPv4 Addresses to MAC Addresses When a packet is sent to the data link layer to be encapsulated into an Ethernet frame, the device refers to a table in its memory to find the MAC address that is mapped to the IPv4 address. This table is called the ARP table or the ARP cache. The ARP table is stored in the RAM of the device. The sending device will search its ARP table for a destination IPv4 address and a corresponding MAC address. If the packet's destination IPv4 address is on the same network as the source IPv4 address, the device will search the ARP table for the destination IPv4 address. If the destination IPv4 address is on a different network than the source IPv4 address, the device will search the ARP table for the IPv4 address of the default gateway. In both cases, the search is for an IPv4 address and a corresponding MAC address for the device. Each entry, or row, of the ARP table binds an IPv4 address with a MAC address. We call the relationship between the two values a map - it simply means that you can locate an IPv4 address in the table and discover the corresponding MAC address. The ARP table temporarily saves (caches) the mapping for the devices on the LAN. If the device locates the IPv4 address, its corresponding MAC address is used as the destination MAC address in the frame. If there is no entry is found, then the device sends an ARP request.

Ethernet Evolution

Since the creation of Ethernet in 1973, standards have evolved for specifying faster and more flexible versions of the technology. This ability for Ethernet to improve over time is one of the main reasons it has become so popular. Early versions of Ethernet were relatively slow at 10 Mbps. The latest versions of Ethernet operate at 10 Gigabits per second and faster. Scroll through the timeline. At the data link layer, the frame structure is nearly identical for all speeds of Ethernet. The Ethernet frame structure adds headers and trailers around the Layer 3 PDU to encapsulate the message being sent

Frame forwarding methods

Store and forwarding Buffers freemen's until the full frame has been received by switch. Checks the frame for errors before releasing it out of its switch ports if full frame was not received, the switch discord's it. A great method to use to conserve bandwidth on a network Cut though No error checking on frames is preformed by the switch before releasing the frame out of its ports The destination network interface card nic discards any incomplete frames using this frame forwarding method. The faster switching method but may produce more errors in a data integrity therefore more bandwidth my be consumed.

MAC Address Tables

Stores the port of MAC address mappings.

Frame Forwarding Methods on Cisco Switches

Switches use one of the following forwarding methods for switching data between network ports: Store-and-forward switching Cut-through switching Figure 1 highlights differences between these two methods. In store-and-forward switching, when the switch receives the frame, it stores the data in buffers until the complete frame has been received. During the storage process, the switch analyzes the frame for information about its destination. In this process, the switch also performs an error check using the Cyclic Redundancy Check (CRC) trailer portion of the Ethernet frame. CRC uses a mathematical formula, based on the number of bits (1s) in the frame, to determine whether the received frame has an error. After confirming the integrity of the frame, the frame is forwarded out the appropriate port, toward its destination. When an error is detected in a frame, the switch discards the frame. Discarding frames with errors reduces the amount of bandwidth consumed by corrupt data. Store-and-forward switching is required for Quality of Service (QoS) analysis on converged networks where frame classification for traffic prioritization is necessary. For example, voice over IP data streams need to have priority over web-browsing traffic.

ARP reply

The ARP reply is a unicast response, containing the desired information, sent to the requestor's link layer address. An even rarer usage of ARP is gratuitous ARP, where a machine announces its ownership of an IP address on a media segment. The arping utility can generate these gratuitous ARP frames.

Frame Check Sequence Field (FCS)

The Frame Check Sequence (FCS) field (4 bytes) is used to detect errors in a frame. It uses a cyclic redundancy check (CRC). The sending device includes the results of a CRC in the FCS field of the frame. The receiving device receives the frame and generates a CRC to look for errors. If the calculations match, no error occurred. Calculations that do not match are an indication that the data has changed; therefore, the frame is dropped. A change in the data could be the result of a disruption of the electrical signals that represent the bits.

What are the functions of LLC & Mac?

The LLC header contains a control field like HDLC and is used for flow and error control. The two access point fields (DSAP and SSAP) define the upper layer protocol at the source and destination that uses LLC. In general, multiple access methods include random access, controlled access and channelisation.

What is the purpose of the layer 2 LLC sublayer?

The LLC sub-layer acts as an interface between the Media Access Control (MAC) sublayer and the network layer. As the Ethertype in an Ethernet II framing formatted frame is used to multiplex different protocols on top of the Ethernet MAC header it can be seen as LLC identifier.

Frame Processing

The MAC address is often referred to as a burned-in address (BIA) because, historically, this address is burned into ROM (Read-Only Memory) on the NIC. This means that the address is encoded into the ROM chip permanently. Note: On modern PC operating systems and NICs, it is possible to change the MAC address in software. This is useful when attempting to gain access to a network that filters based on BIA. Consequently, filtering or controlling traffic based on the MAC address is no longer as secure. When the computer starts up, the first thing the NIC does is copy the MAC address from ROM into RAM. When a device is forwarding a message to an Ethernet network, it attaches header information to the frame. The header information contains the source and destination MAC address. Click Play in the animation to view the frame forwarding process. When a NIC receives an Ethernet frame, it examines the destination MAC address to see if it matches the device's physical MAC address stored in RAM. If there is no match, the device discards the frame. If there is a match, it passes the frame up the OSI layers, where the de-encapsulation process takes place. Note: Ethernet NICs will also accept frames if the destination MAC address is a broadcast or a multicast group of which the host is a member. Any device that can be the source or destination of an Ethernet frame must be assigned a MAC address. This includes workstations, servers, printers, mobile devices, and routers.

What is media access control protocol?

The Media Access Control (MAC) data communication Networks protocol sub-layer, also known as the Medium Access Control, is a sub-layer of the data link layer specified in the seven-layer OSI model. ... In LAN nodes uses the same communication channel for transmission.

What is the function of MAC sublayer?

The Media Access Control Layer is one of two sublayers that make up the Data Link Layer of the OSI model. The MAC layer is responsible for moving data packets to and from one Network Interface Card (NIC) to another across a shared channel.

What is the role of Logical Link Control sublayer?

The function of the Logical Link Control (LLC) is to manage and ensure the integrity of data transmissions. The LLC provides Data Link Layer links to services for the Network Layer protocols. ... Also, there is a LLC Control field for delivery requests or services.

What is the difference between Ethernet and Internet?

The main difference between internet and ethernet is that the internet is a wide area network (WAN) while the ethernet is a local area network (LAN). Internet refers to a worldwide large network that connects a large number of devices around the world. ... On the other hand, ethernet connect devices in a local location.

What is Ethernet frame size?

The original Ethernet IEEE 802.3 standard defined the minimum Ethernet frame size as 64 bytes and the maximum as 1518 bytes. The maximum was later increased to 1522 bytes to allow for VLAN tagging. The minimum size of an Ethernet frame that carries an ICMP packet is 74 bytes.

Ethernet II

The original Ethernet frame type developed by Digital Equipment Corporation, Intel, and Xerox, before the IEEE began to standardize Ethernet. Ethernet II is distinguished from other Ethernet frame types in that it contains a 2-byte type field to identify the upperlayer protocol contained in the frame. It supports TCP/IP and other higher-layer protocols

Media Access Control (MAC)

The second responsibility of the MAC sublayer is media access control. Media access control is responsible for the placement of frames on the media and the removal of frames from the media. As its name implies, it controls access to the media. This sublayer communicates directly with the physical layer. The underlying logical topology of Ethernet is a multi-access bus; therefore, all nodes (devices) on a single network segment share the medium. Ethernet is a contention-based method of networking. A contention-based method means that any device can try to transmit data across the shared medium whenever it has data to send. The Carrier Sense Multiple Access/Collision Detection (CSMA/CD) process is used in half-duplex Ethernet LANs to detect and resolve collisions. Today's Ethernet LANs use full-duplex switches, which allow multiple devices to send and receive simultaneously with no collisions.

How many types of ARP are there?

There are four types of arp messages that may be sent by the arp protocol. These are identified by four values in the "operation" field of an arp message. The types of message are: ARP request.

Source MAC Address Field

This 6-byte field identifies the frame's originating NIC or interface. Must be a unicast address.

Data Field

This field (46 - 1500 bytes) contains the encapsulated data from a higher layer, which is a generic Layer 3 PDU, or more commonly, an IPv4 packet. All frames must be at least 64 bytes long. If a small packet is encapsulated, additional bits called a pad are used to increase the size of the frame to this minimum size.

Is Mac a Layer 2?

This topic provides an introduction to the MAC sublayer of the data link layer (Layer 2). ... The MAC sublayer acts as an interface between the logical link control (LLC) Ethernet sublayer and Layer 1 (the physical layer). The MAC sublayer emulates a full-duplex logical communication channel in a multipoint network.

How do you show an ARP table?

To display the ARP cache entry for a specific IP address, use arp -a with the InetAddr parameter, where InetAddr is an IP address. To display the ARP cache table for a specific interface, use the -N IfaceAddr parameter where IfaceAddr is the IP address assigned to the interface.

Why ARP is required?

Typically, a host uses ARP to determine the hardware address of another host. Your system maintains a table that maps IP addresses to MAC addresses of different systems and routers on your network. ... The ARP protocol creates entries as needed.

What is the ARP command?

Using the arp command allows you to display and modify the Address Resolution Protocol (ARP) cache. An ARP cache is a simple mapping of IP addresses to MAC addresses. ... If they're different, that two computers are assigned the same IP address.

Sending a Frame to the Default Gateway

When a device has an IP address that is on a remote network, the Ethernet frame cannot be sent directly to the destination device. Instead, the Ethernet frame is sent to the MAC address of the default gateway, the router.

Is ARP reply unicast or broadcast?

When a device makes an ARP request, it sends a broadcast and includes the its source MAC address, so the reply can be unicast to the requester. The device that owns the requested address (or a device acting as its proxy) sees the broadcast and unicasts the response.

What are remote routes?

When a router forwards a packet to a host, such as a web server, that host is on the same network as a router's directly connected network. A remote network is a network that is not directly connected to the router. ... Static routes are routes to networks that a network administrator manually configured.

Where is the ARP table stored?

Where is the ARP Cache stored. It is stored in memory: The address resolution protocol (ARP) cache is a table in computer memory that maps a limited number of IP addresses to their physical adapter addresses.

Which type of address is used in an Ethernet frame header?

Which type of address is used in an ethernet frame header? Encapsulated data defined by the Network Access layer is called an Ethernet frame. An Ethernet frame starts with a header, which contains the source and destination MAC addresses, among other data.

cut-through switching

a switching method that begins the forwarding process as soon as enough information has been received to make a forwarding decision the switch acts upon the data as soon as it is received, even if the transmission is not complete. The switch buffers just enough of the frame to read the destination MAC address so that it can determine to which port to forward the data. The destination MAC address is located in the first 6 bytes of the frame following the preamble. The switch looks up the destination MAC address in its switching table, determines the outgoing interface port, and forwards the frame onto its destination through the designated switch port. The switch does not perform any error checking on the frame. There are two variants of cut-through switching: Fast-forward switching - Fast-forward switching offers the lowest level of latency. Fast-forward switching immediately forwards a packet after reading the destination address. Because fast-forward switching starts forwarding before the entire packet has been received, there may be times when packets are relayed with errors. This occurs infrequently, and the destination network adapter discards the faulty packet upon receipt. In fast-forward mode, latency is measured from the first bit received to the first bit transmitted. Fast-forward switching is the typical cut-through method of switching. Fragment-free switching - In fragment-free switching, the switch stores the first 64 bytes of the frame before forwarding. Fragment-free switching can be viewed as a compromise between store-and-forward switching and fast-forward switching. The reason fragment-free switching stores only the first 64 bytes of the frame is that most network errors and collisions occur during the first 64 bytes. Fragment-free switching tries to enhance fast-forward switching by performing a small error check on the first 64 bytes of the frame to ensure that a collision has not occurred before forwarding the frame. Fragment-free switching is a compromise between the high latency and high integrity of store-and-forward switching, and the low latency and reduced integrity of fast-forward switching.

What is Auto MDIX Cisco?

auto-MDIX enabled, either type of cable can be used to connect to other devices, and the interface automatically adjusts to communicate successfully. On newer Cisco routers and switches, the mdix auto interface configuration mode command enables the feature.

Introduction to ARP

every device with an IP address on an Ethernet network also has an Ethernet MAC address. When a device sends an Ethernet frame, it contains these two addresses: Destination MAC address - The MAC address of the Ethernet NIC, which will be either the MAC address of the final destination device or the router. Source MAC address - The MAC address of the sender's Ethernet NIC. To determine the destination MAC address, the device uses ARP. ARP provides two basic functions: Resolving IPv4 addresses to MAC addresses Maintaining a table of mappings

Removing Entries from an ARP Table

or each device, an ARP cache timer removes ARP entries that have not been used for a specified period of time. The times differ depending on the device's operating system. For example, some Windows operating systems store ARP cache entries for 2 minutes. Commands may also be used to manually remove all or some of the entries in the ARP table. After an entry has been removed, the process for sending an ARP request and receiving an ARP reply must occur again to enter the map in the ARP table.

What is ARP cheating?

the Address Resolution Protocol (ARP) is the standard protocol for finding a host´s MAC Address when only its IP Address is known. Via modifying IP Address or MAC Address to achieve ARP cheat, it will be a large challenge for data transmitting normally.

What is MAC layer in LTE?

the LTE MAC layer or the Medium Access Control protocol. MAC is a radio network protocol which resides both in the UE and in the E-UTRAN. ... RRC (Radio Resource Control) protocol is in control of the configuration of MAC that means RRC decides how MAC will behave.

Destination Remote Network

the destination IP address is on a remote network, the destination MAC address will be the address of the host's default gateway, the router's NIC, as shown in the figure. Using a postal analogy, this would be similar to a person taking a letter to their local post office. All they need to do is take the letter to the post office and then it becomes the responsibility of the post office to forward the letter on towards its final destination. the Ethernet MAC addresses and IPv4 addresses for PC-A sending an IP packet to a web server on a remote network. Routers examine the destination IPv4 address to determine the best path to forward the IPv4 packet. This is similar to how the postal service forwards mail based on the address of the recipient. When the router receives the Ethernet frame, it de-encapsulates the Layer 2 information. Using the destination IP address, it determines the next-hop device, and then encapsulates the IP packet in a new data link frame for the outgoing interface. Along each link in a path, an IP packet is encapsulated in a frame specific to the particular data link technology associated with that link, such as Ethernet. If the next-hop device is the final destination, the destination MAC address will be that of the device's Ethernet NIC. How are the IPv4 addresses of the IPv4 packets in a data flow associated with the MAC addresses on each link along the path to the destination? This is done through a process called Address Resolution Protocol (ARP).

unicast MAC address

the unique address used when a frame is sent from a single transmitting device to a single destination device. a host with IPv4 address 192.168.1.5 (source) requests a web page from the server at IPv4 unicast address 192.168.1.200. For a unicast packet to be sent and received, a destination IP address must be in the IP packet header. A corresponding destination MAC address must also be present in the Ethernet frame header. The IP address and MAC address combine to deliver data to one specific destination host. The process that a source host uses to determine the destination MAC address is known as Address Resolution Protocol (ARP). ARP is discussed later in this chapter. Although the destination MAC address can be a unicast, broadcast, or multicast address, the source MAC address must always be a unicast.

Memory Buffering on Switches

there are two methods of memory buffering: port-based and shared memory. Port-based Memory Buffering In port-based memory buffering, frames are stored in queues that are linked to specific incoming and outgoing ports. A frame is transmitted to the outgoing port only when all the frames ahead of it in the queue have been successfully transmitted. It is possible for a single frame to delay the transmission of all the frames in memory because of a busy destination port. This delay occurs even if the other frames could be transmitted to open destination ports. Shared Memory Buffering Shared memory buffering deposits all frames into a common memory buffer that all the ports on the switch share. The amount of buffer memory required by a port is dynamically allocated. The frames in the buffer are linked dynamically to the destination port. This allows the packet to be received on one port and then transmitted on another port, without moving it to a different queue. The switch keeps a map of frame to port links showing where a packet needs to be transmitted. The map link is cleared after the frame has been successfully transmitted. The number of frames stored in the buffer is restricted by the size of the entire memory buffer and not limited to a single port buffer. This permits larger frames to be transmitted with fewer dropped frames. This is especially important to asymmetric switching. Asymmetric switching allows for different data rates on different ports. This allows more bandwidth to be dedicated to certain ports, such as a port connected to a server.

EtherType Field

this 2 byte field identifies the upper layer protocol encapsulated in Ethernet frame. Common values are, in hexadecimal, 0x800, 0x86DD for IPv6 and 0x806 for ARP

What is the primary purpose of ARP?

translate URLs to IP addresses resolve IPv4 addresses to MAC addresses provide dynamic IP configuration to network devices convert internal private addresses to external public addresses 2.

Preamble and Start Frame Delimiter Fields

used for synchronization between the sending and receiving devices. Used to get the attention of the receiving nodes.

Why was Ethernet invented?

Bob Metcalfe invented Ethernet in 1973 while at Xerox PARC, and the company patented it in 1975. Metcalfe and others then finalized an open Ethernet standard in 1980, and by 1985 it had become an IEEE standard. An industry was born, and Ethernet was ready for its meteoric rise.