Tài liệu học CCNA kỳ 3 ccna3 mod4 switchingconcepts

1 1 Module 4 Switching Concepts CCNA 3 version 3.1 Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 2 Contents • Introduction to Ethernet/802.3 LANs • Introduction to LAN Switching • Switch Operation 2 Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 3 Ethernet/802.3 LAN development The earliest LAN technologies commonly used either thick Ethernet or thin Ethernet infrastructures Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 4 Ethernet/802.3 LAN development ( cont…) • A hub is a Layer 1 device. • Sometimes referred to as an Ethernet concentrator or a multi-port repeater. • Allowed greater access to the network for more users. • Active hubs also allowed for the extension of networks to greater distances. • A hub does not make any decisions when receiving data signals. It simply regenerates and amplifies the data signals 3 Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 5 Ethernet/802.3 LAN development ( cont…) • Layer 2 devices are more intelligent than Layer 1 devices. • Layer 2 devices make forwarding decisions based on Media Access Control (MAC) • A bridge is a Layer 2 device. • Bridge collect and pass frames between two network segments. • Bridges control traffic to the network. • Bridges do not restrict broadcast traffic. Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 6 Ethernet/802.3 LAN development ( cont…) • A switch is also a Layer 2 device and may be referred to as a multi-port bridge. • Make forwarding decisions based on MAC addresses. • Create a virtual circuit between two connected devices that want to communicate. • Also able to facilitate multiple, simultaneous virtual circuit connections. • Forward broadcast frames to all connected devices on the network. 4 Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 7 Ethernet/802.3 LAN development ( cont…) • A router is a Layer 3 device. • Makes decisions based on groups of network addresses, or classes. • Use routing tables to record the Layer 3 addresses of the networks. • Not compelled to forward broadcasts. • Reduce the size of both the collision domains and the broadcast domains in a network . Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 8 Ethernet/802.3 LAN development ( cont…) • LANs typically employ a combination of Layer 1, Layer 2, and Layer 3 devices. • Implementation of these devices depends on factors that are specific to the particular needs of the organization. 5 Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 9 Factors that impact network performance • Too many users on a 10-Mbps segment • Most users accessing one or two servers • Network-intensive applications such as color publishing, CAD/CAM, imaging and relational databases Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 10 Elements of Ethernet/802.3 networks • Ethernet is used to transport data between devices on a network. • These devices include computers, printers, and file servers… 6 Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 11 Elements of Ethernet/802.3 networks (cont…) The performance of a shared medium Ethernet/802.3 LAN can be negatively affected by several factors: • The data frame delivery of Ethernet/802.3 LANs is of a broadcast nature. • The carrier sense multiple access/collision detect (CSMA/CD) method allows only one station to transmit at a time. • Multimedia applications with higher bandwidth demand such as video and the Internet, coupled with the broadcast nature of Ethernet, can create network congestion. • Normal latency occurs as the frames travel across the Layer 1 medium and through Layer 1, Layer 2, and Layer 3 networking devices. • Extending the distances and increasing latency of the Ethernet/802.3 LANs by using Layer 1 repeaters. Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 12 Elements of Ethernet/802.3 networks (cont…) • Ethernet using CSMA/CD and a shared medium can support data transmission rates of up to 100 Mbps. • CSMA/CD is an access method that allows only one station to transmit at a time. 7 Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 13 Elements of Ethernet/802.3 networks (cont…) A certain number of collisions are expected in the design of Ethernet and CSMA/CD Æ collisions can become a major problem in a CSMA/CD network. Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 14 Network congestion • The requirements have exceeded the 10 Mbps available on shared Ethernet/802.3 LANs • Today's networks are experiencing an increase in the transmission of many forms of media: – Large graphics files – Images – Full-motion video – Multimedia applications 8 Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 15 Network latency Latency, or delay, is the time a frame or a packet takes to travel from the source station to the final destination. Latency has at least three sources: • The time source NIC place voltage pulses on the wire and the time the receiving NIC interpret these pulses. • The actual propagation delay as the signal takes time to travel along the cable. • Latency is added according to which networking devices. Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 16 Ethernet 10 BASE-T transmission time Transmission time equals the number of bits being sent times the bit time for a given technology Another way to think about transmission time is the time it takes a frame to be transmitted. 9 Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 17 The benefits of using repeaters • Allow a longer end-to-end distance • Increase the collision domain size • Increase the broadcast domain size Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 18 Full-duplex transmitting • Allows the transmission of a packet and the reception of a different packet at the same time • Requires the use of two pairs of wires • Collision-free transmission • Offers 100% of the bandwidth in both directions 10 Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 19 LAN segmentation • A network can be divided into smaller units called segments • Why segment LANs ? – Isolates traffic between segments – Achieves more bandwidth per user by creating smaller collision domains Họcviệnmạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 20 LAN segmentation ( cont … ) • Each segment uses the CSMA/CD access method and maintains traffic between users on the segment. • Each segment is its own collision domain. • Segmentation allows network congestion to be significantly reduced • Devices within a segment share the total available bandwidth [...]... www.ciscobachkhoa.com 30 15 Layer 2 switching Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 31 Layer 3 switching Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 32 16 Symmetric switching A symmetric switch provides switched connections between ports with the same bandwidth Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 33 Asymmetric switching • An asymmetric... between sending and receiving hosts Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 42 21 Switches and collision domains switch Collision Domains • A switch employs “microsegmentation” to reduce the collision domain on a LAN 33 33 1111 • The switch does this by creating dedicated network segments, or point-to-point Abbreviated MAC addresses 2222 4444 connections Học viện mạng Cisco Bách Khoa... data frames – Maintaining switching operations Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 25 Basic operations of a switch (cont…) Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 26 13 Basic operations of a switch (cont…) Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 27 Basic operations of a switch (cont…) Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com... existing 802 .3 (CSMA/CD) compliant network interface cards and cabling • All hosts connected to the switch are still in the same broadcast domain Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 23 LAN segmentation with switches (cont…) Virtual network circuit is established within the switch and exists only when the nodes need to communicate maximum available bandwidth Học viện mạng... memory buffering Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 34 17 Memory buffering • In port-based memory buffering frames are stored in queues that are linked to specific incoming ports • Shared memory buffering deposits all frames into a common memory buffer which all the ports on the switch share Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 35 Switching methods... do not need to be forwarded from the local segment Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 21 LAN segmentation with routers • • • • • More manageable, greater functionality, multiple active paths Smaller broadcast domains Operates at Layer 3 Adding a latency factor of 20% to 30 % over a switched network Not forward broadcasts Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com... entire frame is received Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 36 18 Switching methods (cont…) • • The following are two forms of cut-through switching: Fast-forward – switching immediately forwards a packet after reading the destination address Fragment-free – Fragment-free switching filters out collision fragments ( < 64 bytes ) before forwarding begins Học viện mạng Cisco Bách... www.ciscobachkhoa.com 37 Frame transmission modes • • • Fast-forward - immediately forwards a packet after reading the destination address Store-and-forward – the entire frame is received before any forwarding takes place Fragment-free – reads the first 64 bytes of an Ethernet frame and then begins forwarding it to the appropriate port or ports Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 38 19 Frame... for the destination address Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 40 20 How switches and bridges filter frames • Switches flood frames that are: – Unknown unicasts – Layer 2 broadcasts – Multicasts (unless running multicast snooping or IGMP) – Multicast are special layer 2 and layer 3 addresses that are sent to devices that belong to that “group” Học viện mạng Cisco Bách Khoa... (cont…) Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 29 Ethernet switch latency • • Latency is the period of time from when the beginning of a frame enters to when the end of the frame exits the switch Directly related to the configured switching process and volume of traffic Measured in fractions of a second Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com 30 15 Layer