ITCS217 Lecture 13 - Ethernet PDF 2024

MAHIDOL UNIVERSITY Faculty of Information and Communication Technology Lecture 13 Ethernet Novem...

MAHIDOL UNIVERSITY Faculty of Information and Communication Technology Lecture 13 Ethernet November 2024 Wisdom of the Land 1 MAHIDOL UNIVERSITY, FACULTY OF ICT 2  MAHIDOL UNIVERSITY, FACULTY OF ICT Quotes of the Day Walk with the Wise and Become Wise, but the Companion of Fools will be Destroyed. Proverbs 13:20 Not to associate with fools; To associate with the wise (ไม่คบคนพาล; คบบัณฑิต) Man Gala Sutta (มงคลสูตร 38) Image by jcomp on Freepik 3  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet We learn that there are many protocols and techniques in the data-link layer and physical layer. It is usually used in Local Area Network (LAN). Too many protocols create too many problems and confusion to the end consumer (too flexible like a PC computer). To simplify the protocols, a specific standard (de facto standard) is established. This is called ‘Ethernet’ that is easy to use by most people and support the Internet. Ethernet is a protocol that covers both data-link layer and physical layer together into one standard. 4  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet in OSI Model 5  MAHIDOL UNIVERSITY, FACULTY OF ICT History 6  MAHIDOL UNIVERSITY, FACULTY OF ICT Today 7  MAHIDOL UNIVERSITY, FACULTY OF ICT History Ethernet was developed at Xerox PARC between 1973 and 1974. It was inspired by ALOHAnet, which a Xerox employee, Robert Metcalfe, had studied as part of his PhD dissertation. Metcalfe left Xerox in 1978 to form 3Com a famous network company (now acquired by HP). Matcalfe convinced Digital Equipment Corporation, Intel and Xerox to promote Ethernet as a standard. Ethernet initially competed with expensive IBM’s Token Ring and other proprietary protocols. Ethernet was able to adapt to market needs and with 10BASE2, shift to inexpensive thin coaxial cable and from 1990, to the now-ubiquitous twisted pair with 10BASE-T (UTP) which completely kills Token Ring and other proprietary protocols for the PC market (1995 onwards). 8  MAHIDOL UNIVERSITY, FACULTY OF ICT Dealing with Shared Medium In the 1980s and 1990s several different types of shared-medium LANs were used. All of these LANs used a media-access method to solve the problem of sharing the media. The early Ethernet used the CSMA/CD approach. Competing technologies such as the Token Ring, Token Bus, and FDDI (Fiber Distribution Data Interface) used the token-passing approach. During this period, another LAN technology, ATM LAN, which is deployed in the high speed WAN technology (ATM), also appeared in the market. LAN Internet LAN Application Application Application (e.g. HTTP) (e.g. HTTP) (e.g. HTTP) Layer 5 TCP/IP TCP/IP TCP/IP Layer 3+4 Ethernet ATM Ethernet Layer 1+2 9  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Standard In February 1980, the Institute of Electrical and Electronics Engineers (IEEE) started project 802 (Ethernet) to standardize local area networks (LAN). Data Link Layer Framing Flow control (Ethernet has no flow control) Error control (CRC-32) Media Access Control (CSMA/CD for wired 1983 and CSMA/CA for wireless in 1997) Physical layer Wiring and signaling protocols At the same time, Token Ring (supported by IBM), Token Bus (selected and henceforward supported by General Motors) and FDDI (Fiber Distributed Data Interface supported by ANSI) were also considered as candidates for a LAN standard. Token-based systems were not simple. They need coordination of machines. Plus, the proposed token-based systems were governed by a specific company. It is not open to the community. 10  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Standard In 1983 Ethernet becomes IEEE 802.3 standard for Local Area Network used by billions of people around the world. Almost every LAN except Ethernet has disappeared from the marketplace because Ethernet was able to evolve to meet the needs of higher transmission rates. Ethernet is open to the community. Anyone can manufacture Ethernet devices as long as it follows IEEE 802.3 specification. Ethernet is a cheaper technology than the other competing technologies. 11  MAHIDOL UNIVERSITY, FACULTY OF ICT IEEE Project 802 Early Ethernet focused on the standardization of media access control (MAC) operation and CSMA/CD was pushed to be the standard. Today, Ethernet has evolved to include higher bandwidth, improved medium access control methods, and different physical media. The coaxial cable was replaced with point-to-point links connected by Ethernet repeaters or switches. 12  MAHIDOL UNIVERSITY, FACULTY OF ICT IEEE Project 802 Project 802 was started to unify functions and specifications of the physical layer and the data-link layer of major LAN protocols because There were too many protocols at the time Physical layer and data-link layer have to work closely together. LLC is not a part of At the time, there were many competing technologies IEEE 802.3 standard 13  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet in OSI Model The LLC sublayer handles the communication between the upper layers and the lower layers. This is typically between the networking software and the device hardware. The LLC sublayer takes the network protocol data, which is typically an IPv4 packet, and adds control information to help deliver the packet to the destination node. Ethernet == IEEE 802.3 https://en.wikipedia.org/wiki/IEEE_802 14  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Evolution There are 4 major types of Ethernet. Today, Ethernet can support 40 Gbps and 100 Gbps. Use CSMA/CD CSMA/CD is (Bus or Hub) optional No CSMA/CD (hub only) (switch is used) 15  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Specification (Flow Control) Ethernet provides a connectionless service. Each frame sent is independent of the previous or next frame. Ethernet has no connection establishment or connection termination phases. Since Ethernet has no LLC, the sender sends a frame whenever it has it. The receiver may or may not be ready for it. The sender may overwhelm the receiver with frames, which may result in dropping frames. If a frame drops, the sender will not know about it. We rely on the higher level protocol such as TCP to deal with the frame drop using flow control in the transport layer. Internet protocol (layer 3), which is using the service of Ethernet, is connectionless, it will not know about a frame drop. If the transport layer is also a connectionless protocol, such as UDP, the frame is lost and salvation may only come from the application layer. However, if the transport layer is TCP, the sender TCP does not receive acknowledgment for its segment and sends it again. 16  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Specification (Error Control) Ethernet has no LLC (flow control), Ethernet is unreliable like IP and UDP. Data link layer is responsible for flow control. Most real-world implementations just use Ethernet without flow control and leave flow control to transport layer for speed. Ethernet does provide CRC-32 for frame error checking. If a frame is corrupted during transmission and the receiver finds out about the corruption, due to CRC-32, the receiver drops the frame silently. It is the duty of high-level protocols to find out about it and correct it using transport layer protocols. 17  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Specification (Framing) Preamble: This field contains 7 bytes (56 bits) of alternating 0s and 1s that alert the receiving system to the coming frame and enable it to synchronize its clock if it’s out of synchronization. The preamble is actually added at the physical layer and is not (formally) part of the frame. 18  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Specification (Framing) Start frame delimiter (SFD): This field (1 byte: 10101011) signals the beginning of the frame. The SFD warns the station or stations that this is the last chance for synchronization. This field is actually a flag that defines the beginning of the frame. SFD is added at the physical layer. 19  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Specification (Framing) Destination address (DA). This field is six bytes (48 bits) and contains the link-layer address of the destination station or stations to receive the packet. → MAC address Source address (SA). This field is also six bytes and contains the link-layer address of the sender of the packet. Type. This field defines the upper-layer protocol whose packet is encapsulated in the frame. This protocol can be IP, ARP, OSPF, and so on. 20  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Specification (Framing) Data. This field carries data encapsulated from the upper-layer protocols. It is a minimum of 46 and a maximum of 1500 bytes. It has to have a minimum length because of CSMA/CD requirement to listen to the incoming frame. 0-padding is needed if the frame data is too short. CRC. The last field contains error detection information, in this case a CRC-32. The CRC is calculated over the addresses, types, and data field. 21  MAHIDOL UNIVERSITY, FACULTY OF ICT 64 bytes is from Ethernet Frame Length Lec.12 Slide 58 An Ethernet frame needs to have a minimum length of 512 bits or 64 bytes to support CSMA/CD. Part of this length is the header and the trailer. If we count 18 bytes of header and trailer (6 bytes of source address, 6 bytes of destination address, 2 bytes of length or type, and 4 bytes of CRC), then the minimum length of data from the upper layer is 64 − 18 = 46 bytes. The standard defines the maximum length of a frame (without preamble and SFD field) as 1518 bytes. If we subtract the 18 bytes of header and trailer, the maximum length of the payload is 1500 bytes. This is because Memory was very expensive when Ethernet was designed; a maximum length restriction helped to reduce the size of the buffer. Second, the maximum length restriction prevents one station from monopolizing the shared medium, blocking other stations that have data to send. 22  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Addressing Each station on an Ethernet network (such as a PC, workstation, or printer) has its own network interface card (NIC). The NIC fits inside the station and provides the station with a link-layer address. The Ethernet address is 6 bytes (48 bits), normally written in hexadecimal notation, with a colon between the bytes (e.g., 4A:30:10:21:10:1A). The first 24 bits are manufacturer specific assigned by IEEE (OUI) and the last 24 bits are assigned by manufacturers (vendors). 23  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Addressing 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. 24  MAHIDOL UNIVERSITY, FACULTY OF ICT MAC Spoofing MAC Address spoofing or MAC spoofing is a technique for changing a factory- assigned Media Access Control (MAC) address of a network interface on a networked device. The MAC address that is hard-coded on a network interface controller (NIC) cannot be changed. However, many drivers allow the MAC address to be changed. MAC address spoofing is limited to the local broadcast domain. Unlike IP address spoofing, where senders spoof their IP address in order to cause the receiver to send the response elsewhere In MAC address spoofing, the response is usually received by the spoofing party if switch is not configured to prevent MAC spoofing. To prevent third parties from using the MAC address to track devices, Android, Linux, iOS, and Windows have implemented MAC address randomization. In June 2014, Apple announced that future versions of their iOS platform would randomize MAC addresses for all Wi-Fi connections, making it more difficult for internet service providers to track user activities and identities, which resurrected moral and legal arguments surrounding the practice of MAC spoofing among several blogs and newspapers 25  MAHIDOL UNIVERSITY, FACULTY OF ICT MAC Spoofing https://www.howtogeek.com/192173/how-and-why-to-change- your-mac-address-on-windows-linux-and-mac/ Example Linux MacOS Windows 26  MAHIDOL UNIVERSITY, FACULTY OF ICT Using Addresses to Transmit Frames The way the addresses are sent out online is different from the way they are written in hexadecimal notation. The transmission is left to right, byte by byte; however, for each byte, the least significant bit is sent first and the most significant bit is sent last. This means that the bit that defines an address as unicast or multicast arrives first at the receiver. This helps the receiver to immediately know if the packet is unicast or multicast. Sent first 27  MAHIDOL UNIVERSITY, FACULTY OF ICT MAC Address Types 28  MAHIDOL UNIVERSITY, FACULTY OF ICT Transmission of Addresses Example: Show how the address 47:20:1B:2E:08:EE is sent out online. 29  MAHIDOL UNIVERSITY, FACULTY OF ICT Transmission of Addresses For Standard Ethernet or traditional Ethernet, the physical layer is shared medium. All transmission will be broadcasted anyway. Then, what do we do about the unicast, multicast and broadcast addresses? In a unicast transmission, all stations will receive the frame, the intended recipient keeps and handles the frame; the rest discard it. In a multicast transmission, all stations will receive the frame, the stations that are members of the group keep and handle it; the rest discard it. In a broadcast transmission, all stations (except the sender) will receive the frame and all stations (except the sender) keep and handle it. 30  MAHIDOL UNIVERSITY, FACULTY OF ICT Broadcast, Multicast and Unicast 31  MAHIDOL UNIVERSITY, FACULTY OF ICT Unicast Frame Transmission 32  MAHIDOL UNIVERSITY, FACULTY OF ICT Broadcast Frame Transmission 33  MAHIDOL UNIVERSITY, FACULTY OF ICT Multicast Frame Transmission 34  MAHIDOL UNIVERSITY, FACULTY OF ICT Broadcast and Multicast Broadcast Usually broadcast operations involve the use of protocols that requires broadcasting to get information from a network such as DHCP and ARP. Multicast 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. A host subscribes to a Multicast group using IGMP protocol (not for this course) Multicast helps the sender by reducing the number of frames that the sender has to send out. Routers/switches will help duplicate multicast frames and send them through ports. Multicast addresses would be used in multiplayer online 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 The multicast IP address requires a corresponding multicast MAC address to actually deliver frames on a local network. 35 Let’s have a Break ! 36  MAHIDOL UNIVERSITY, FACULTY OF ICT Sending Data from LAN to another LAN Sending a frame from one LAN to another LAN (involve OSI Layers) https://www.youtube.com/watch?v=zhlMLRNY5-4 https://www.youtube.com/watch?v=O7CuFlM4V54 https://www.youtube.com/watch?v=-6Uoku-M6oY More info about Ethernet frame structure https://www.youtube.com/watch?v=_b4dXKB8Pt8 Cisco CCNA1 course Data encapsulation https://www.youtube.com/watch?v=xaKvGnnuYmk 37  MAHIDOL UNIVERSITY, FACULTY OF ICT Communicating on a Local Network 38  MAHIDOL UNIVERSITY, FACULTY OF ICT Communicating to a Remote Network 39  MAHIDOL UNIVERSITY, FACULTY OF ICT Standard Ethernet (Access Method) Only Standard Ethernet requires CSMA/CD. The Standard Ethernet chose CSMA/CD with 1- persistent method. The sender continues to listen during transmission. A station sending a minimum frame length of 64 bytes (512 bits). Reason: If we consider the transmission rate of the Ethernet as 10 Mbps, this means that it takes the station 512/(10 Mbps) = 51.2 s to send out 512 bits. With the speed of propagation in a cable (2 x 108 m/s), the first bit could have gone 10,240 meters (one way) or only 5120 meters (round trip), have collided with a bit from the last station on the cable, and have gone back. In other words, if a collision were to occur, it should occur by the time the sender has sent out 512 bits (worst case) and the first bit has made a round trip of 5120 meters. However, in practice, the maximum cable length is 2,500 meters to compensate for the delay in the medium. 40  MAHIDOL UNIVERSITY, FACULTY OF ICT History In the 1980s and 1990s several different types of LANs were used. Most of them use the concept of shared medium. 10Base5 Bus (Thick Ethernet) 10Base2 Bus (Thin Ethernet) 41  MAHIDOL UNIVERSITY, FACULTY OF ICT History 10BaseT Star (Hub) 10BaseT Star (Switch) 42  MAHIDOL UNIVERSITY, FACULTY OF ICT History 10Base-F Star (Fiber Hub) 43  MAHIDOL UNIVERSITY, FACULTY OF ICT Thick Ethernet (10Base-5) The first commercially available Ethernet (1982) Coaxial cable 44  MAHIDOL UNIVERSITY, FACULTY OF ICT Thin Ethernet (10Base-2) Coaxial cable 45  MAHIDOL UNIVERSITY, FACULTY OF ICT 10Base-T Ethernet Twisted Pair Cable 46  MAHIDOL UNIVERSITY, FACULTY OF ICT Cables 47  MAHIDOL UNIVERSITY, FACULTY OF ICT Backward Compatibility 48  MAHIDOL UNIVERSITY, FACULTY OF ICT Standard Ethernet (Physical Layer) 49  MAHIDOL UNIVERSITY, FACULTY OF ICT Medium Sharing In a Standard Ethernet network, the total capacity (10 Mbps) is shared among all stations with a frame to send; the stations share the bandwidth of the network. If only one station has frames to send, it benefits from the total capacity (10 Mbps). But if more than one station needs to use the network, the capacity is shared. If two stations try to send, each station will get 5 Mbps. This means that the more computers you have, the slower you get. 50  MAHIDOL UNIVERSITY, FACULTY OF ICT Dividing and Connecting 2 LANs Placing a bridge to a Standard Ethernet can help separate collision domain. This can increase the data transfer rate within a small segment of the network. A bridge is essentially a 2 port switch. It can determine whether a frame should be forwarded to the other side of the network. 51  MAHIDOL UNIVERSITY, FACULTY OF ICT Switched Ethernet A switch is essentially a N-port bridge. The collision domain is separated into N subdomains. Each subdomain can enjoy the full 10 Mbps transfer rate. Collision will never happen. So, CSMA/CD is not needed!!! To fully use the subdomain, full duplex transmission is implemented. 52  MAHIDOL UNIVERSITY, FACULTY OF ICT Fast Ethernet (100 Mbps) Hub-based Fast Ethernet The minimum frame size is still 64 bytes. However, the frames will be sent 10 times faster. So, with the influence of CSMA/CD, the maximum length of the cable is reduced from 2,500 meters to 250 meters. In practice, we use the limit of 100 m. Switched Fast Ethernet CSMA/CD is not needed. The link-layer switch receives a frame from a source host and stores it in the buffer (queue) waiting for processing. It then checks the destination address and sends the frame out of the corresponding interface. Since the connection to the switch is full-duplex, the destination address can even send a frame to another station at the same time that it is receiving a frame. In other words, the shared medium is changed to many point-to-point media, and there is no need for contention. 53  MAHIDOL UNIVERSITY, FACULTY OF ICT Backward Compatibility When a 10 Mbps LAN is bridged (through a switch or hub) with 100 Mbps LAN, Fast Ethernet has autonegotiation function which allows the two devices to negotiate the speed of transmission (usually use the slower one). 54  MAHIDOL UNIVERSITY, FACULTY OF ICT Fast Ethernet (Physical Layer) How to make the network run faster? Answer: Increase the signaling bandwidth (baud rate). However, Manchester encoding needs a 200-Mbaud bandwidth for a data rate of 100 Mbps, which makes it unsuitable for a medium such as twisted-pair cable. So, we replace Manchester encoding with MLT-3 is used to increase level (increase data rate) 4B/5B is used to provide synchronization to support MLT-3. 8B/6T is used to provide more levels and synchronization 55  MAHIDOL UNIVERSITY, FACULTY OF ICT Fast Ethernet (Physical Layer) 56  MAHIDOL UNIVERSITY, FACULTY OF ICT Gigabit Ethernet A complete new design of the protocol called IEEE 802.3z. Support speed of 1 Gbps Compatible with Standard and Fast Ethernet using autonegotiation Use the same framing specification. Increase the minimum frame length to 512 bytes (4096 bits) from 64 bytes (512 bits). This is called Carrier Extension. There is no collision due to the use of switch and full-duplex mode. There is no Gigabit Ethernet hub. If the frame length is not 512 bytes, padding will be applied. However, multiple frames can be joined together to form a larger frame. This is called Frame Bursting. 57  MAHIDOL UNIVERSITY, FACULTY OF ICT Gigabit Ethernet (Physical Layer) Encoding 58  MAHIDOL UNIVERSITY, FACULTY OF ICT 10 Gigabit Ethernet Only Fiber optics cable can be used. The new standard is called 802.3ae. Characteristics Same frame size and format as 1 Gigabit Ethernet. Improve interconnection with MAN and WAN. Physical layer 59  MAHIDOL UNIVERSITY, FACULTY OF ICT Summary of Standards 60  MAHIDOL UNIVERSITY, FACULTY OF ICT History Year 1973 1980 1983 1985 Standard Ethernet DIX Standard for IEEE 802.3 10Base-5 IEEE 802.3a 10Base-2 Ethernet II Description Ethernet invented Digital Equipment 10 Mbps Ethernet 10 Mbps Ethernet by Dr. Robert Corp, Intel and Xerox over thick coaxial over thin coaxial Metcalf of Xerox (DIX) released a cable cable standard for 10 Mbps Ethernet over coaxial cable Year 1990 1993 1995 1998 Standard IEEE 802.3i 10Base-T IEEE 802.3j 10Base-F IEEE 802.3u 100Base-xx IEEE 802.3z 1000Base-X Description 10 Mbps Ethernet 10 Mbps Ethernet Fast Ethernet 100 Mbps Gigabit Ethernet over twisted-pair over fiber optic cable over twisted pair and over fiber optics cable fiber optics 61  MAHIDOL UNIVERSITY, FACULTY OF ICT History Year 1985 1999 2002 2006 Standard IEEE 802.3a IEEE 802.3ab IEEE 802.3ae IEEE 802.3an 10Base-2 1000Base-T 10GBase-xx 10G Base-T Description 10 Mbps Gigabit Ethernet 802.3at (Power Power over Ethernet over over twisted pair over Ethernet) Ethernet thin coaxial cable enhancements cable Year 2009 2015 2016 2017 Standard IEEE 802.3at (PoE) 100GbE and 40GbE 2.5GBase-T and IEEE 802.3bs 5GBase-T 200 GbE & 400GbE Description Power over 100G/40G for 2.5 Gbps and 5 200 & 400 Gigabit Ethernet Optical Fiber Gbps over Twisted- Ethernet over fiber enhancements Pair cable optics 62  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Switch Hub and Switch operation https://www.youtube.com/watch?v=eMamgWllRFY Learning MAC address The switch dynamically builds the MAC address table by examining the source MAC address of the frames received on a port. If the source MAC address does not exist, it is added to the table along with the incoming port number. Most Ethernet switches keep an entry in the table for 5 minutes. If the source MAC address does exist in the table but on a different port, the switch treats this as a new entry. The entry is replaced using the same MAC address but with the more current port number. 63  MAHIDOL UNIVERSITY, FACULTY OF ICT Ethernet Switch Forwarding The switch forwards frames by searching for a match between the destination MAC address in the frame and an entry in the MAC address table. If the destination MAC address is in the table, it will forward the frame out the specified port. This is also called frame filtering. If the destination MAC address is not in the table, the switch will forward the frame out all ports (connecting to computers) except the incoming port. This is known as an unknown unicast. If the destination MAC address is a broadcast or a multicast, the frame is also flooded out all ports except the incoming port. 64  MAHIDOL UNIVERSITY, FACULTY OF ICT Connected Switches A switch can have multiple MAC addresses associated with a single port. This is common when the switch is connected to another switch. The switch will have a separate MAC address table entry for each frame received with a different source MAC address. 65  MAHIDOL UNIVERSITY, FACULTY OF ICT Sending Frame outside LAN 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. The sending device knows about the MAC address of the default gateway through DHCP. 66  MAHIDOL UNIVERSITY, FACULTY OF ICT Example Given the following switch configuration, Where will the switch forward this frame to? Frame MAC Table 67  MAHIDOL UNIVERSITY, FACULTY OF ICT Example What will this switch do for each following scenario? Switch receives a frame from a source address not in its MAC table. Switch receives a frame that has destination address in its MAC table. Switch receives a frame that has destination address NOT in its MAC table. Switch receives a frame that has destination address is a broadcast address. Frame MAC Table 68  MAHIDOL UNIVERSITY, FACULTY OF ICT Example What will this switch do for each following scenario? Switch receives a frame from a source address NOT in its MAC table. Switch puts the source’s MAC address in its MAC table along with the associated port. Switch receives a frame that has destination address in its MAC table. Switch forwards the frame to the port associated with the destination address. Switch receives a frame that has destination address NOT in its MAC table. Switch broadcasts the frame to all the ports that is up except the incoming port. Switch receives a frame that has destination address is a broadcast address. Switch broadcasts the frame to all the ports that is up except the incoming port. 69  MAHIDOL UNIVERSITY, FACULTY OF ICT Types of Ethernet Switch Store-and-forward switch This switch receives the entire frame, checks the frame for error using CRC, and look up the destination address and forward the frame if CRC is valid. Required for Quality of Service (QoS) mechanism to learn the type of frame to provide privilege service. Cut-through switch This switch forwards the frame before it is entirely received by looking at the destination address of the frame first. Good for fast forwarding that does not need QoS. There are two types Fast forwarding switch (basic type) Fragment-free switch (check first 64 bytes for error – remember CSMA/CD) 70  MAHIDOL UNIVERSITY, FACULTY OF ICT Switching Fabric Queues at input and output ports Port-based memory queue (each port) vs. Shared memory queue (all ports) 71  MAHIDOL UNIVERSITY, FACULTY OF ICT Example Fill in the blanks 72  MAHIDOL UNIVERSITY, FACULTY OF ICT Auto Medium Detection Connections between specific devices, such as switch-to-switch, switch-to-router, switch-to-host, and router-to-host devices, once required the use of specific cable types (crossover or straight-through). Most switch devices now support the mdix auto interface configuration command in the CLI to enable the automatic medium-dependent interface crossover (auto- MDIX) feature. When the auto-MDIX feature is enabled, the switch detects the type of cable attached to the port, and configures the interfaces accordingly. Therefore, you can use either a crossover or a straight-through cable for connections to a copper 10/100/1000 port on the switch, regardless of the type of device on the other end of the connection. 73  MAHIDOL UNIVERSITY, FACULTY OF ICT End of the Slides Don’t Forget to do Exercise 13 ☺ 74