Ethernet - Chapter 9: Network fundamentals

Ethernet Network Fundamentals – Chapter 9 Học viện mạng Bach Khoa - Website: www.bkacad.com Objectives • Identify the basic characteristics of network media used in Ethernet. • Describe the physical and data link features of Ethernet. • Describe the function and characteristics of the media access control method used by Ethernet protocol. • Explain the importance of Layer 2 addressing used for data transmission and determine how the different types of addressing impacts network operation and performance. • Compare and contrast the application and benefits of using Ethernet switches in a LAN as apposed to using hubs. • Explain the ARP process. Học viện mạng Bach Khoa - Website: www.bkacad.com Học viện mạng Bach Khoa - Website: www.bkacad.com Overview of Ethernet Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet – Standards and Implementation 9.1.1 Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet – Standards and Implementation IEEE (Electrical and Electronics Engineers) Standards • The first LAN is the original version of Ethernet. Robert Metcalfe and his coworkers at Xerox designed it more than 30 years ago. – The first Ethernet standard was published in 1980 by a consortium of Digital Equipment Corporation, Intel, and Xerox (DIX). It was released as an open standard. The first Ethernet standard products were sold in the early 1980s. • In 1985, the IEEE standards committee for Local and Metropolitan Networks published standards for LANs. These standards start with the number 802, and 802.3 is for Ethernet. To compare to the International Standards Organization (ISO) and OSI model, the IEEE 802.3 standards had to address the needs of Layer 1 and the lower portion of Layer 2 of the OSI model. As a result, some small modifications to the original Ethernet standard were made in 802.3. Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet – Layer 1 and Layer 2 9.1.2 Học viện mạng Bach Khoa - Website: www.bkacad.com LLC – Connecting to the Upper Layers • LLC is implemented in software, and its implementation is independent of the physical equipment. • In a computer, the LLC can be considered the driver software (?) for the Network Interface Card (NIC). The NIC driver is a program that interacts directly with the hardware on the NIC to pass the data between the media and the Media Access Control sublayer. The use of these sublayers contributes significantly to compatibility between diverse end devices. Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: The structure of LLC Học viện mạng Bach Khoa - Website: www.bkacad.com MAC – Getting Data to the Media • The framing process provides important delimiters that are used to identify a group of bits that make up a frame. This process provides synchronization between the transmitting and receiving nodes. 9.1.4 Học viện mạng Bach Khoa - Website: www.bkacad.com Physical and Implementations of Ethernet 9.1.5 Học viện mạng Bach Khoa - Website: www.bkacad.com Physical and Implementations of Ethernet • The success of Ethernet is due to the following factors: 1. Simplicity and ease of maintenance 2. Ability to incorporate new technologies 3. Reliability 4. Low cost of installation and upgrade The introduction of Gigabit Ethernet has extended the original LAN technology to distances that make Ethernet a Metropolitan Area Network (MAN) and WAN standard. Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet – Communication through the LAN Học viện mạng Bach Khoa - Website: www.bkacad.com Historic Ethernet 9.2.1.1 Học viện mạng Bach Khoa - Website: www.bkacad.com Historic Ethernet 9.2.1.2 Học viện mạng Bach Khoa - Website: www.bkacad.com Historic Ethernet • Early Ethernet Media: Coaxial cable – Logical and physical bus topology – 10BASE5, or Thicknet, used a thick coaxial that allowed for cabling distances of up to 500 meters before the signal required a repeater. – 10BASE2, or Thinnet, used a thin coaxial cable that was smaller in diameter and more flexible than Thicknet and allowed for cabling distances of 185 meters. • Now, it was replaced by UTP cables. – The UTP cables were easier to work with, lightweight, and less expensive. – Physical topology was a star topology using hubs. • Hubs concentrate connections. • Any single cable to fail without disrupting the entire network. • Repeating the frame to all other ports did not solve the issue of collisions. Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet Collision Management Legacy Ethernet • In 10BASE-T networks, typically using a hub. – This created a shared media. – Only one station could successfully transmit at a time: half-duplex communication. • More devices, more collisions. • Using CSMA/CD to manage collisions, with little or no impact on performance. As the number of devices and subsequent data traffic increase, however, the rise in collisions can have a significant impact on the user's experience. 9.2.2 Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet Collision Management Current Ethernet • 100BASE-TX Ethernet. Switches replace hubs • Switches can control the flow of data by isolating each port and sending a frame only to its proper destination (if the destination is known), rather than send every frame to every device. • The switch reduces or minimizes the possibility of collisions. • Support full-duplex communications (transmit and receive signals at the same time) • 1Gbps Ethernet and beyond. Học viện mạng Bach Khoa - Website: www.bkacad.com Move to 1Gbps and Beyond • The applications tax even the most robust networks. – For example, the increasing use of Voice over IP (VoIP) and multimedia services requires connections that are faster than 100 Mbps Ethernet. • 1000 Mbps (Gigabit) Ethernet is used. • Some of the equipment and cabling in modern, well-designed and installed networks may be capable of working at the higher speeds with only minimal upgrading. This reduces the total cost. Học viện mạng Bach Khoa - Website: www.bkacad.com Move to 1Gbps and Beyond Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Metro Ethernet Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet Frame Học viện mạng Bach Khoa - Website: www.bkacad.com The Frame – Encapsulating the Packet 9.3.1 Học viện mạng Bach Khoa - Website: www.bkacad.com The Frame – Encapsulating the Packet • Ethernet II is the Ethernet frame format that is used in TCP/IP networks. Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet frame structure •The Preamble is used for timing synchronization in the asynchronous 10 Mbps and slower implementations of Ethernet. Faster versions of Ethernet are synchronous, and this timing information is redundant but retained for compatibility. • Note: the timing information represented by the preamble and SFD is discarded and not counted toward the minimum and maximum frame size. 10101011 Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet frame structure •The Destination Address field contains the MAC destination address. It can be unicast, multicast (group), or broadcast (all nodes) •The Source Address is generally the unicast address of the transmitting Ethernet node (can be virtual entity – group or multicast). 10101011 Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet frame structure •The Type value specifies the upper-layer protocol to receive the data after Ethernet processing is completed. •The Length indicates the number of bytes of data that follows this field. (so contents of the Data field are decoded per the protocol indicated). Length if value < 1536 decimal, (0x600)
need LLC to identify upper protocol Type if value >= 1536 decimal, (0x600)
it identify upper protocol 4 bytes CRC Học viện mạng Bach Khoa - Website: www.bkacad.com • Three functions of the upper data link sublayer in the OSI model 1. Identifies the network layer protocol 2. Makes the connection with the upper layers 3. Insulates network layer protocols from changes in physical equipment Remember for sublayer LLC Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet frame structure •The Maximum Transmission Unit (MTU) for Ethernet is 1500 octets, so the data should not exceed that size • Ethernet requires that the frame be not less than 46 octets or more than 1500 octets (Pad is required if not enough data). • The IEEE 802.3ac standard, released in 1998, extended the maximum allowable frame size to 1522 bytes. •The frame size was increased to accommodate a technology called Virtual Local Area Network (VLAN). Length if value < 1536 decimal, (0x600)
need LLC to identify upper protocol Type if value >= 1536 decimal, (0x600)
it identify upper protocol 4 bytes CRC Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet frame structure • A FCS contains a 4-byte CRC value that is created by the device that sends data and is recalculated by the destination device to check for damaged frames. Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Ethernet frame structure •The data field must be at least 46 bytes long. •This length assures that the frame signals stay on the network long enough for every Ethernet station on the network system to hear the frame within the correct time limits. •Every station must hear the frame within the maximum round-trip signal propagation time of an Ethernet system. Học viện mạng Bach Khoa - Website: www.bkacad.com The Ethernet MAC Address 9.3.2 Học viện mạng Bach Khoa - Website: www.bkacad.com •Ethernet uses MAC addresses that are 48 bits in length and expressed as 12 hexadecimal digits. •Sometimes referred to as burned-in addresses (BIA) because they are burned into read-only memory (ROM) and are copied into random-access memory (RAM) when the NIC initializes. The Ethernet MAC Address Học viện mạng Bach Khoa - Website: www.bkacad.com Hexadecimal Numbering and Addressing 9.3.3 Học viện mạng Bach Khoa - Website: www.bkacad.com Hexadecimal Numbering and Addressing • Hexadecimal Numbering: The base 16 numbering system uses the numbers 0 to 9 and the letters A to F. • Understanding Bytes: 8 bits (a byte) is a common binary grouping, binary 00000000 to 11111111 can be represented in hexadecimal as the range 00 to FF. • Representing Hexadecimal Values: preceded by 0x (for example 0x73) • 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. Học viện mạng Bach Khoa - Website: www.bkacad.com Hexadecimal Numbering and Addressing Học viện mạng Bach Khoa - Website: www.bkacad.com Another Layer of Addressing 9.3.4 Học viện mạng Bach Khoa - Website: www.bkacad.com Another Layer of Addressing Data Link Layer • OSI Data Link layer (Layer 2) physical addressing, implemented as an Ethernet MAC address, is used to transport the frame across the local media. – Although providing unique host addresses, physical addresses are non-hierarchical (Flat !). – They are associated with a particular device regardless of its location or to which network it is connected. • These Layer 2 addresses have no meaning outside the local network media. – A packet may have to traverse a number of different Data Link technologies in local and wide area networks before it reaches its destination. – A source device therefore has no knowledge of the technology used in intermediate and destination networks or of their Layer 2 addressing and frame structures. Học viện mạng Bach Khoa - Website: www.bkacad.com Another Layer of Addressing Network Layer • Network layer (Layer 3) addresses, such as IPv4 addresses, provide the ubiquitous, logical addressing that is understood at both source and destination. To arrive at its eventual destination, a packet carries the destination Layer 3 address from its source. However, as it is framed by the different Data Link layer protocols along the way, the Layer 2 address it receives each time applies only to that local portion of the journey and its media. In short: • The Network layer address enables the packet to be forwarded toward its destination. • The Data Link layer address enables the packet to be carried by the local media across each segment. Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet Unicast 9.3.5 Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet Broadcast Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet Multicast The source will always have a unicast address. Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: IP Multicast address
MAC Multicats address Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet Media Access Control Học viện mạng Bach Khoa - Website: www.bkacad.com Media Access Control in Ethernet Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: CSMA/CD Listen-before-transmit Transmitting& listening Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: CSMA/CD CSMA/CD used in Ethernet performs 3 functions: 1.Transmitting and receiving data packets 2.Decoding data packets and checking them for valid addresses before passing them to the upper layers of the OSI model 3.Detecting errors within data packets or on the network Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: CSMA/CD • Carrier Sense Multiple Access (CSMA): when a NIC has data to transmit, the NIC first listens to the cable (using a transceiver) to see if a carrier (signal) is being transmitted by another node. This may be achieved by monitoring whether a current is flowing in the cable (each bit corresponds to 18-20 milliAmps (mA)). • Collision Detection (CD) : when there is data waiting to be sent, each transmitting NIC also monitors its own transmission. If it observes a collision (excess current above what it is generating, i.e. > 24 mA for coaxial Ethernet), it stops transmission immediately and instead transmits a 32-bit jam sequence. Học viện mạng Bach Khoa - Website: www.bkacad.com CSMA/CD – The Process 9.4.2.1 Học viện mạng Bach Khoa - Website: www.bkacad.com CSMA/CD – The Process Học viện mạng Bach Khoa - Website: www.bkacad.com CSMA/CD – The Process Học viện mạng Bach Khoa - Website: www.bkacad.com CSMA/CD – The Process • After an Ethernet collision, when the backoff algorithm is invoked, which device has priority to transmit data? • Any device in the collision domain whose backoff timer expires first • What’s a drawback of the CSMA/CD access method? • Collisions can decrease network performance Học viện mạng Bach Khoa - Website: www.bkacad.com CSMA/CD – The Process • Hubs and Collision Domains (?) 9.4.2.2 Học viện mạng Bach Khoa - Website: www.bkacad.com Lab 9.4.2.3 Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet Timing This accumulated delay increases the collisions because a listening node may transition while the hub or repeater is processing the message 9.4.3.1 Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Ethernet delay/latency Listen - Free ? - Transmit 1 0 1 0 1 delay latency Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet Timing • Ethernet 10Mbps and slower are asynchronous. • Ethernet 100Mbps and higher are synchronous. • However, for compatibility reasons, the Preamble and Start Frame Delimiter (SFD) fields are still present. 9.4.3.2 Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet Timing 9.4.3.3 Bit Time: For each different media speed, a period of time is required for a bit to be placed and sensed on the media. This period of time is referred to as the bit time. Example: 10Mbps: 10^7 bit/10^9 nano second (ns)
1bit at the MAC sublayer requires 100ns to transmit. Ethernet Timing • For CSMA/CD Ethernet to operate, the sending device must become aware of a collision before it has completed transmission of a minimum-sized frame. •Why ? Học viện mạng Bach Khoa - Website: www.bkacad.com 9.4.3.3 Ethernet Timing Slot time ? Học viện mạng Bach Khoa - Website: www.bkacad.com 9.4.3.3 Học viện mạng Bach Khoa - Website: www.bkacad.com Interframe Spacing and Backoff • Interframe Spacing: this time is measured from the last bit of the FCS field of one frame to the first bit of the Preamble of the next frame. 9.4.4.1 Học viện mạng Bach Khoa - Website: www.bkacad.com Interframe Spacing and Backoff Jam Signal • As soon as a collision is detected, the sending devices transmit a 32-bit "jam" signal that will enforce the collision. This ensures all devices in the LAN to detect the collision. 9.4.4.2 Học viện mạng Bach Khoa - Website: www.bkacad.com Interframe Spacing and Backoff Học viện mạng Bach Khoa - Website: www.bkacad.com Interframe Spacing and Backoff • After 16 attempts, it gives up and generates an error to the Network layer. 9.4.4.3 Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Ethernet slot time Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Ethernet slot time Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Ethernet slot time Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Ethernet slot time Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Slot time on 1000Mbps Ethernet Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Backoff Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Backoff k=min (n,10); n= the number of transmission attempts r=random (0,2^k) The backoff delay = r* slot time Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet Physical Layer Học viện mạng Bach Khoa - Website: www.bkacad.com Overview of Ethernet Physical Layer Học viện mạng Bach Khoa - Website: www.bkacad.com 10Mbps and 100Mbps Ethernet • 10BASE5 using Thicknet coaxial cable • 10BASE2 using Thinnet coaxial cable • 10BASE5, and 10BASE2 used coaxial cable in a physical bus. No longer used; and are not supported by the newer 802.3 standards. 10BASE-T: • 10BASE-T (in 1990) used cheaper and easier to install Category 3 unshielded twisted pair (UTP) copper cable rather than coax cable. The cable plugged into a central connection device (the shared bus), this device was a hub. • This is referred to as a star topology. The distances the cables could extend from the hub via another hub referred to as an extended star topology. • Originally 10BASE-T was a half-duplex protocol, but full-duplex features were added later. • 10BASE-T : Manchester encoding, max. 100 meter horizontal cable, use RJ-45 connectors 9.5.2.1 Học viện mạng Bach Khoa - Website: www.bkacad.com 10Mbps and 100Mbps Ethernet Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: 10Mbps Ethernet Common timing parameters Common frame format (Exponent) r=random(0,2^k) k=min(n,10) The wating period=r*slot time Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: 5-4-3-2-1 Rule • The 5-4-3-2-1 rule requires that the following guidelines should not be exceeded: – 5 segments of network media – 4 repeaters or hubs – 3 host segments of the network – 2 link sections (no hosts) – 1 large collision domain Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Signal Quality Error AUI transceiver cable Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Signal Quality Error Học viện mạng Bach Khoa - Website: www.bkacad.com 10Mbps and 100Mbps Ethernet • 100-Mbps Ethernet is also known as Fast Ethernet. • The two technologies that have become important are 100BASE-TX, which is a copper UTP medium and 100BASE-FX, which is a multimode optical fiber medium. 9.5.2.2 Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: 100Mbps Ethernet Học viện mạng Bach Khoa - Website: www.bkacad.com 1000Mbps Ethernet 1000 Mbps - Gigabit Ethernet • The development of Gigabit Ethernet standards resulted in specifications for UTP copper, single-mode fiber, and multimode fiber. • Encoding and decoding data is more complex. • Gigabit Ethernet uses 2 separate encoding steps. 1000BASE-T Ethernet • 1000BASE-T Ethernet provides full-duplex transmission using all four pairs in Category 5 or later UTP cable. – Gigabit Ethernet over copper wire enables an increase from 100 Mbps per wire pair to 125 Mbps per wire pair, or 500 Mbps for the four pairs. – Each wire pair signals in full duplex, doubling the 500 Mbps to 1000 Mbps. • 1000BASE-T uses 4D-PAM5 line encoding to obtain 1 Gbps data throughput. 9.5.3.1 Học viện mạng Bach Khoa - Website: www.bkacad.com Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Gigabit and 10-Gigabit Ethernet •At the physical layer, the bit patterns from the MAC layer are converted into symbols. •The symbols may also be control information such as start frame, end frame, medium idle conditions Fiber-based Gigabit Ethernet (1000BASE-X) uses 8B/10B encoding, this is followed by the simple Non-Return to Zero (NRZ) line encoding of light on optical fiber Học viện mạng Bach Khoa - Website: www.bkacad.com 1000Mbps Ethernet Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Compare 10,100BaseT with 1000BaseT • “BI” stands for bi-directional, while DA, DB, DC and DD stand for “Data A”, “Data B”, “Data C” and “Data D”, respectively: • One pair is used for transmitting data and the other pair is used for receiving data. Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Gigabit Ethernet on copper • As might be expected, this results in a permanent collision on the wire pairs. – These collisions result in complex voltage patterns. • With the complex integrated circuits using techniques such as echo cancellation, Layer 1 Forward Error Correction (FEC), and prudent selection of voltage levels, the system achieves the 1Gigabit throughput. – The 1000BASE-T system uses a set of digital signal processing (DSP) techniques. These include echo cancellation, near-end crosstalk (NEXT) cancellation and far-end crosstalk (FEXT) cancellation. – Another DSP technique is signal equalization, to help compensate for signal distortion over the channel. • The 1000BASE-T transceiver also scrambles the signal to spread out the electromagnetic emission patterns in the data to help avoid signal emission from the cable. Học viện mạng Bach Khoa - Website: www.bkacad.com 1000Mbps Ethernet 9.5.3.2 Full-duplex binary transmission at 1250 Mbps over two strands of optical fiber. The transmission coding is based on the 8B/10B encoding scheme. Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet – Future Options 9.5.4 Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet – Future Options Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet – Future Options Future Ethernet Speeds • Although 1-Gigabit Ethernet is now widely available and 10-Gigabit products are becoming more available, the IEEE and the 10-Gigabit Ethernet Alliance are working on 40-, 100-, or even 160-Gbps standards. • The technologies that are adopted will depend on a number of factors, including the rate of maturation of the technologies and standards, the rate of adoption in the market, and the cost of emerging products. Học viện mạng Bach Khoa - Website: www.bkacad.com Hubs and Switches Học viện mạng Bach Khoa - Website: www.bkacad.com Legacy Ethernet – Using Hubs • Using hubs to interconnect nodes: – not perform any type of traffic filtering – forwards all the bits to every device – share the bandwidth • High levels of collisions on the LAN, so this type of Ethernet LAN has limited use: typically in small LANs or in LANs with low bandwidth. • Some of the issues: – Scalability – Latency – Network Failure – Collisions 9.6.1 Học viện mạng Bach Khoa - Website: www.bkacad.com Legacy Ethernet – Using Hubs Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Layer 2 bridging Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet – Using Switches Switches allow the segmentation of the LAN into separate collision domains. 9.6.2.1 Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet – Using Switches • In a LAN where all nodes are connected directly to the switch, the throughput of the network increases dramatically. • The three primary reasons for this increase are: 1. Dedicated bandwidth to each port 2. Collision-free environment 3. Full-duplex operation 9.6.2.2 Học viện mạng Bach Khoa - Website: www.bkacad.com Ethernet – Using Switches Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Switch Characteristic • Content-addressable memory (CAM) is memory that essentially works backwards compared to conventional memory. • An application-specific integrated circuit (ASIC) is a device consisting of undedicated logic gates that can be programmed to perform functions at logic speeds. Lab 9.6.2 Học viện mạng Bach Khoa - Website: www.bkacad.com Học viện mạng Bach Khoa - Website: www.bkacad.com Hubs vs Switches • Why not use switches in every Ethernet LAN? • Three reasons why hubs are still being used: – Availability – Economics – Requirements Học viện mạng Bach Khoa - Website: www.bkacad.com Switches – Selective Forwarding 9.6.3.1 Học viện mạng Bach Khoa - Website: www.bkacad.com Switches – Selective Forwarding •MAC Table •Switch Table •Bridge Table Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: Switching Modes Học viện mạng Bach Khoa - Website: www.bkacad.com Switches – Selective Forwarding • Switch Operation: 1. Learning: The MAC table must be populated with MAC addresses and their corresponding ports. 2. Aging: to remove old entries in the MAC table. 3. Flooding: sends the unknown frame to all ports except the port on which the frame arrived. 4. Selective Forwarding: forwards the frame to the corresponding port. 5. Filtering: not forward a frame. 9.6.3.2 Học viện mạng Bach Khoa - Website: www.bkacad.com Switches – Selective Forwarding 9.6.3.2 Học viện mạng Bach Khoa - Website: www.bkacad.com Activity 9.6.4.1 Lab 9.6.4.2 Học viện mạng Bach Khoa - Website: www.bkacad.com Học viện mạng Bach Khoa - Website: www.bkacad.com Address Resolution Protocol Học viện mạng Bach Khoa - Website: www.bkacad.com Address Resolution Protocol (ARP) • In order for devices to communicate, the sending devices need both the IP addresses and the MAC addresses of the destination devices. • The ARP protocol provides two basic functions: 1. Resolving IPv4 addresses to MAC addresses 2. Maintaining a cache of mappings Học viện mạng Bach Khoa - Website: www.bkacad.com Address resolution protocol Học viện mạng Bach Khoa - Website: www.bkacad.com ARP table in host Học viện mạng Bach Khoa - Website: www.bkacad.com 197.15.22.33 A.B.C.1.3.3 197.15.22.126 A.B.C.7.3.5 197.15.22.34 A.B.C.4.3.4 A B C ARP operation ARP Table: ? MAC A.B.C.1.3.3 MAC ? IP 197.15.22.33 IP 197.15.22.126 Data Học viện mạng Bach Khoa - Website: www.bkacad.com 197.15.22.33 A.B.C.1.3.3 197.15.22.126 A.B.C.7.3.5 197.15.22.34 A.B.C.4.3.4 A B C ARP operation: ARP request MAC A.B.C.1.3.3 MAC ff.ff.ff.ff.ff.ff IP 197.15.22.33 IP 197.15.22.126 What is your MAC Addr? Học viện mạng Bach Khoa - Website: www.bkacad.com 197.15.22.33 A.B.C.1.3.3 197.15.22.126 A.B.C.7.3.5 197.15.22.34 A.B.C.4.3.4 A B C ARP operation: Checking MAC A.B.C.1.3.3 MAC ff.ff.ff.ff.ff.ff IP 197.15.22.33 IP 197.15.22.126 What is your MAC Addr? Học viện mạng Bach Khoa - Website: www.bkacad.com 197.15.22.33 A.B.C.1.3.3 197.15.22.126 A.B.C.7.3.5 197.15.22.34 A.B.C.4.3.4 A B C ARP operation: ARP reply MAC A.B.C.7.3.5 MAC A.B.C.1.3.3 IP 197.15.22.126 IP 197.15.22.33 This is my MAC Addr Học viện mạng Bach Khoa - Website: www.bkacad.com 197.15.22.33 A.B.C.1.3.3 197.15.22.126 A.B.C.7.3.5 197.15.22.34 A.B.C.4.3.4 A B C ARP operation: Caching ARP Table: A.B.C.7.3.5 – 197.15.22.126 MAC A.B.C.1.3.3 MAC A.B.C.7.3.5 IP 197.15.22.33 IP 197.15.22.126 Data Học viện mạng Bach Khoa - Website: www.bkacad.com The ARP Process 9.7.1 Học viện mạng Bach Khoa - Website: www.bkacad.com ARP – Destination Outside the Local Network 9.7.2.1 Học viện mạng Bach Khoa - Website: www.bkacad.com Proxy ARP 9.7.2.2 Học viện mạng Bach Khoa - Website: www.bkacad.com Proxy ARP Học viện mạng Bach Khoa - Website: www.bkacad.com ARP – Removing Address Mappings • 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 and its operating system. – For example, some Windows operating systems store ARP cache entries for 2 minutes. If the entry is used again during that time, the ARP timer for that entry is extended to 10 minutes. • Commands may also be used to manually remove all or some of the entries in the ARP table. Học viện mạng Bach Khoa - Website: www.bkacad.com ARP – Removing Address Mappings 9.7.3 Học viện mạng Bach Khoa - Website: www.bkacad.com ARP Broadcasts - Issues • ARP Spoofing • ARP Poisoning Học viện mạng Bach Khoa - Website: www.bkacad.com Extra: ARP poisoning Lab 9.8.1.1-2 Học viện mạng Bach Khoa - Website: www.bkacad.com Học viện mạng Bach Khoa - Website: www.bkacad.com Lab 9.8.2.1-2 Lab 9.8.3.1-2 Học viện mạng Bach Khoa - Website: www.bkacad.com Q&A • Which of the following describe interframe spacing? – the minimum interval, measured in bit- times, that any station must wait before sending another frame – the time allowed for slow stations to process a frame and prepare for the next frame Học viện mạng Bach Khoa - Website: www.bkacad.com Q&A • When a collision occurs in a network using CSMA/CD, how do hosts with data to transmit respond after the backoff period has expired? –The hosts return to a listen-before- transmit mode. Học viện mạng Bach Khoa - Website: www.bkacad.com Q&A • After an Ethernet collision, when the backoff algorithm is invoked, which device has priority to transmit data? –any device in the collision domain whose backoff timer expires first Học viện mạng Bach Khoa - Website: www.bkacad.com Q&A • Which of the following is a drawback of the CSMA/CD access method? –Collisions can decrease network performance. Học viện mạng Bach Khoa - Website: www.bkacad.com Q&A • Which two features make switches preferable to hubs in Ethernet-based networks? –minimizing of collisions –increase in the throughput of communications Học viện mạng Bach Khoa - Website: www.bkacad.com Học viện mạng Bach Khoa - Website: www.bkacad.com Summary Học viện mạng Bach Khoa - Website: www.bkacad.com