Week 5 CLO2 - Implementing Ethernets, and Switched Networks PDF

CIN 2103: Networking Fundamentals Week 5: CLO2 – Implementing Ethernets, and Switched Networks Delivery Outline 2 Computer Networks W1: C...

CIN 2103: Networking Fundamentals Week 5: CLO2 – Implementing Ethernets, and Switched Networks Delivery Outline 2 Computer Networks W1: CLO1 - Explaining modern network technologies principles W2: CLO1 - Explaining network protocols and standards principles W3: CLO2 – Classifying network physical connectivity W4: CLO2 – Implementing media access control, and data link communication W5: CLO2 – Implementing Ethernets, and switched networks W6: CLO3 – Implementing Network layer IP protocols W7-8: CLO3 – Implementing IPv4 subnetting for network segmentation W9: CLO3 – Implementing IPv6 addressing W10: CLO4 – Classifying transport layer protocols operation for end-to-end communication W11: CLO4 – Classifying application layer protocols operation in end-user applications W12: CLO4 – Implementing network hardening features to enhance security W13-14: CLO2-4 – Designing and simulating a small network Week 5 CLO2 – Ethernet Switching  Ethernet Switching 4 Objectives Upon completing this chapter, the learner should be able to understand: LANs using switches. (Chapter 2 of Textbook) Tiered switches. (Chapter 2 of Textbook) Ethernet Switching Responsibilities. (Chapter 6 of Textbook) Frame forwarding. (Chapter 6 of Textbook)  Ethernet Switching 5 LANs using Switches Switches have become the backbone of most organizations' networks and understanding their functionality is an important skill for any IT support member. Not only do switches allow for greater network segmentation, but they also offer full-duplex communication, making them more efficient. Switches operate by learning which of its ports a particular MAC address is connected to and base their forwarding decisions on this knowledge. One of the benefits of using a switch is that all the devices can communicate at the same time.  Ethernet Switching 6 LANs using Switches If Computer C wants to talk to Computer B while Computer A is talking to Computer D, it can. The switch will form a virtual connection between Computer A and Computer D. It will also form another virtual connection between Computer C and Computer B.  Ethernet Switching 7 Tiered Switches The following is an example of an enterprise switched network. As the size of the organization increases, you will start to see a tiered approach being adopted  8 The purpose of switches and switching Ethernet Switching By introducing a switch to our network, we are providing a means of segmenting the network into smaller, more manageable, and more efficient areas. Further segmentation can be provided using VLANs. Each VLAN corresponds to a broadcast domain.  Ethernet Switching 9 Ethernet Frames Ethernet operates in the data link layer and the physical layer. It is a family of networking technologies defined in the IEEE 802.2 and 802.3 standards.  Ethernet Switching 10 Data Link Sublayers The 802 LAN/MAN standards, including Ethernet, use two separate sublayers of the data link layer to operate: LLC Sublayer: (IEEE 802.2) Places information in the frame to identify which network layer protocol is used for the frame. MAC Sublayer: (IEEE 802.3, 802.11, or 802.15) Responsible for data encapsulation and media access control, and provides data link layer addressing.  Ethernet Switching 11 MAC Sublayer The MAC sublayer is responsible for data encapsulation and accessing the media. Data Encapsulation IEEE 802.3 data encapsulation includes the following: 1. Ethernet frame - This is the internal structure of the Ethernet frame. 2. Ethernet Addressing - The Ethernet frame includes both a source and destination MAC address to deliver the Ethernet frame from Ethernet NIC to Ethernet NIC on the same LAN. 3. Ethernet Error detection - The Ethernet frame includes a frame check sequence (FCS) trailer used for error detection.  Ethernet Switching 12 MAC Sublayer Media Access Legacy Ethernet using a bus topology or hubs, is a shared, half- duplex medium. Ethernet over a half-duplex medium uses a contention-based access method, carrier sense multiple access/collision detection (CSMA/CD). Ethernet LANs of today use switches that operate in full-duplex. Full-duplex communications with Ethernet switches do not require access control through CSMA/CD  Ethernet Switching 13 Ethernet Frame Fields The minimum Ethernet frame size is 64 bytes and the maximum is 1518 bytes. The preamble field is not included when describing the size of the frame. Any frame less than 64 bytes in length is considered a “collision fragment” or “runt frame” and is automatically discarded. Frames with more than 1500 bytes of data are considered “jumbo” or “baby giant frames”. If the size of a transmitted frame is less than the minimum, or greater than the maximum, the receiving device drops the frame. Dropped frames are likely to be the result of collisions or other unwanted signals. They are considered invalid. Jumbo frames are usually supported by most Fast Ethernet and Gigabit Ethernet switches and NICs Check Your Understanding 1. Login to NetAcad: https://Netacad.com2. Quiz link: https://contenthub.netacad.com/itn-dl/7.1.5  Ethernet Switching 15 MAC Address and Hexadecimal An Ethernet MAC address consists of a 48-bit binary value, expressed using 12 hexadecimal values. 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. When using hexadecimal, leading zeroes are always displayed to complete the 8-bit representation. For example, the binary value 0000 1010 is represented in hexadecimal as 0A. Hexadecimal numbers are often represented by the value preceded by 0x (e.g., 0x73) to distinguish between decimal and hexadecimal values in documentation. Hexadecimal may also be represented by a subscript 16, or the hex number followed by an H (e.g., 73H).  Ethernet Switching 16 Ethernet MAC Address In an Ethernet LAN, every network device is connected to the same, shared media. MAC addressing provides a method for device identification at the data link layer of the OSI model. An Ethernet MAC address is a 48-bit address expressed using 12 hexadecimal digits. Because a byte equals 8 bits, we can also say that a MAC address is 6 bytes in length. All MAC addresses must be unique to the Ethernet device or Ethernet interface. To ensure this, all vendors that sell Ethernet devices must register with the IEEE to obtain a unique 6 hexadecimal (i.e., 24-bit or 3- byte) code called the organizationally unique identifier (OUI). An Ethernet MAC address consists of a 6 hexadecimal vendor OUI code followed by a 6 hexadecimal vendor-assigned value.  Ethernet Switching 17 Frame Processing When a device is forwarding a message to an Ethernet network, the Ethernet header include a Source MAC address and a Destination MAC address. When a NIC receives an Ethernet frame, it examines the destination MAC address to see if it matches the physical MAC address that is 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 is the source or destination of an Ethernet frame, will have an Ethernet NIC and therefore, a MAC address. This includes workstations, servers, printers, mobile devices, and routers.  Ethernet Switching 18 Unicast MAC address In Ethernet, different MAC addresses are used for Layer 2 unicast, broadcast, and multicast communications. A unicast MAC address is the unique address that is used when a frame is sent from a single transmitting device to a single destination device. The process that a source host uses to determine the destination MAC address associated with an IPv4 address is known as Address Resolution Protocol (ARP). The process that a source host uses to determine the destination MAC address associated with an IPv6 address is known as Neighbor Discovery (ND). Note: The source MAC address must always be a unicast.  Ethernet Switching 19 Broadcast MAC address An Ethernet broadcast frame is received and processed by every device on the Ethernet LAN. The features of an Ethernet broadcast are as follows: It has a destination MAC address of FF-FF-FF- FF-FF-FF in hexadecimal (48 ones in binary). It is flooded out all Ethernet switch ports except the incoming port. It is not forwarded by a router. If the encapsulated data is an IPv4 broadcast packet, this means the 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.  Ethernet Switching 20 Multicast MAC addresscessing An Ethernet multicast frame is received and processed by a group of devices that belong to the same multicast group. There is a destination MAC address of 01-00-5E when the encapsulated data is an IPv4 multicast packet and a destination MAC address of 33-33 when the encapsulated data is an IPv6 multicast packet. There are other reserved multicast destination MAC addresses for when the encapsulated data is not IP, such as Spanning Tree Protocol (STP). It is flooded out all Ethernet switch ports except the incoming port, unless the switch is configured for multicast snooping. It is not forwarded by a router, unless the router is configured to route multicast packets. 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. As with the unicast and broadcast addresses, the multicast IP address requires a corresponding multicast MAC address.  Ethernet Switching 21 The MAC Address Table - Switch Fundamentals A Layer 2 Ethernet switch uses Layer 2 MAC addresses to make forwarding decisions. It is completely unaware of the data (protocol) being carried in the data portion of the frame, such as an IPv4 packet, an ARP message, or an IPv6 ND packet. The switch makes its forwarding decisions based solely on the Layer 2 Ethernet MAC addresses. An Ethernet switch examines its MAC address table to make a forwarding decision for each frame, unlike legacy Ethernet hubs that repeat bits out all ports except the incoming port. When a switch is turned on, the MAC address table is empty Note: The MAC address table is sometimes referred to as a content addressable memory (CAM) table.  Ethernet Switching 22 Switch Learning and Forwarding Examine the Source MAC Address (Learn) Every frame that enters a switch is checked for new information to learn. It does this by examining the source MAC address of the frame and the port number where the frame entered the switch. If the source MAC address does not exist, it is added to the table along with the incoming port number. If the source MAC address does exist, the switch updates the refresh timer for that entry. By default, most Ethernet switches keep an entry in the table for 5 minutes. Note: 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. Find the Destination MAC Address (Forward) If the destination MAC address is a unicast address, the switch will look for a match between the destination MAC address of the frame and an entry in its MAC address table. If the destination MAC address is in the table, it will forward the frame out the specified port. If the destination MAC address is not in the table, the switch will forward the frame out all ports except the incoming port. This is called an unknown unicast. Note: If the destination MAC address is a broadcast or a multicast, the frame is also flooded out all ports except the incoming port.  Ethernet Switching 23 The MAC Address Table - 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 MAC address table of the switch contains the destination MAC address, it is able to filter the frame and forward out a single port. Check Your Understanding 1. Login to NetAcad: https://Netacad.com2. Activity link: https://contenthub.netacad.com/itn-dl/7.3.6  Ethernet Switching 25 Methods of frame forwarding Switches have intelligence built into them to prevent devices from receiving all the data being sent on the network, even if it isn't destined for them. Switches use two methods of forwarding data: Cut-through switching (faster) Store and forward  Ethernet Switching 26 Cut-through switching In cut-through switching, 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 it should forward out the data. The switch does not perform any error checking on the frame. There are two variants of cut-through switching: Fast-forward switching - Offers the lowest level of latency by immediately forwarding 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. The destination NIC discards the faulty packet upon receipt. Fast-forward switching is the typical cut-through method of switching. Fragment-free switching - 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, the switch stores and performs an error check on the first 64 bytes of the frame before forwarding. Because most network errors and collisions occur during the first 64 bytes, this ensures that a collision has not occurred before forwarding the frame.  Ethernet Switching 27 Cut-through switching - Fast-forward switching In cut-through switching, the switch forwards the data almost immediately. At a minimum, it just needs to know the destination MAC addresses. As soon as it has this information, it will forward the data, even if the whole frame hasn't been received by the switch. A simplified visualization of this can be seen in Figure 6.2 (Fast- forward switching): step 1, the frame is being sent. step 2, the switch receives the destination MAC address. step 3, the switch starts to forward the frame, even though it's only received the destination MAC address. steps 4 and 5, the switch continues to send the remainder of the frame.  Ethernet Switching 28 Store and forward switching In this process, the switch will store the frame data in its memory buffer until the complete frame has been received. Once the frame has been completely received, the switch will perform error checking on the data before forwarding the frame on. Any corrupt frames are discarded. Store and forward also allows data to be prioritized through Quality of Service (QoS). We can see a simplified visualization of this in Figure 6.3: Step 1, the frame is being sent. Step 2, the switch receives the destination MAC address. Step 3, the switch holds on to (stores) the frame. Step 4, the switch now has all of the frames it will carry out the error check on. Step 5, the switch forwards the frame(s) on if they passed the error check.  Ethernet Switching 29 Memory Buffering on Switches An Ethernet switch may use a buffering technique to store frames before forwarding them or when the destination port is busy because of congestion. Method Description 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 in the queue Port-based memory 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. Deposits all frames into a common memory buffer shared by all switch ports and the amount of buffer memory required by a port is dynamically allocated. Shared memory The frames in the buffer are dynamically linked to the destination port enabling a packet to be received on one port and then transmitted on another port, without moving it to a different queue. Shared memory buffering also results in larger frames that can be transmitted with fewer dropped frames. This is important with asymmetric switching which allows for different data rates on different ports. Therefore, more bandwidth can be dedicated to certain ports (e.g., server port).  Ethernet Switching 30 Duplex and Speed Settings An Ethernet switch may use a buffering technique to store frames before forwarding them or when the destination port is busy because of congestion. Two of the most basic settings on a switch are the bandwidth (“speed”) and duplex settings for each individual switch port. It is critical that the duplex and bandwidth settings match between the switch port and the connected devices. There are two types of duplex settings used for communications on an Ethernet network: Full-duplex - Both ends of the connection can send and receive simultaneously. Half-duplex - Only one end of the connection can send at a time. Autonegotiation is an optional function found on most Ethernet switches and NICs. It enables two devices to automatically negotiate the best speed and duplex capabilities. Note: Gigabit Ethernet ports only operate in full-duplex.  Ethernet Switching 31 Duplex and Speed Settings Duplex mismatch is one of the most common causes of performance issues on 10/100 Mbps Ethernet links. It occurs when one port on the link operates at half-duplex while the other port operates at full-duplex. This can occur when one or both ports on a link are reset, and the autonegotiation process does not result in both link partners having the same configuration. It also can occur when users reconfigure one side of a link and forget to reconfigure the other. Both sides of a link should have autonegotiation on, or both sides should have it off. Best practice is to configure both Ethernet switch ports as full-duplex.  Ethernet Switching 32 Auto-MDIX Connections between devices once required the use of either a crossover or straight-through cable. The type of cable required depended on the type of interconnecting devices. Note: A direct connection between a router and a host requires a cross-over connection. Most switch devices now support the automatic medium-dependent interface crossover (auto-MDIX) feature. When enabled, the switch automatically detects the type of cable attached to the port and configures the interfaces accordingly. The auto-MDIX feature is enabled by default on switches running Cisco IOS Release 12.2(18)SE or later. However, the feature could be disabled. For this reason, you should always use the correct cable type and not rely on the auto-MDIX feature. Auto-MDIX can be re-enabled using the mdix auto interface configuration command. Check Your Understanding 1. Login to NetAcad: https://Netacad.com2. Quiz link: https://contenthub.netacad.com/itn-dl/7.4.6 Test my understanding 1. Login to NetAcad: https://Netacad.com2. Module 7 Quiz Modules 4 - 7: Ethernet Concepts Exam 1. Login to NetAcad: https://Netacad.com2. Exam Link: Module 4-7 Exam  Thank You 800 MyHCT (800 www.hct.ac.ae 69428)