Lecture CCNA Exploration 4.0 (Kỳ 3) - Chapter 2: Basic switch concepts and configurations

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This chapter summarize the operation of Ethernet as defined for 100/1000 Mbps LANs in the IEEE 802.3 standard. Explain the functions that enable a switch to forward Ethernet frames in a LAN. Configure a switch for operation in a network designed to support voice, video, and data transmissions. Configure basic security on a switch that will operate in a network designed to support voice, video, and data transmissions.

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Nội dung Text: Lecture CCNA Exploration 4.0 (Kỳ 3) - Chapter 2: Basic switch concepts and configurations

Chapter 2: Basic switch concepts and configurations CCNA Exploration 4.0 1
Overview Học viện mạng Bach Khoa - Website: www.bkacad.com 2
Key elements of Ethernet/802.3 networks Học viện mạng Bach Khoa - Website: www.bkacad.com 3
Media Access Control (MAC) Deterministic, Non-Deterministic •MAC refers to protocols that logical bus determine which computer topology and on a shared-medium physical star or environment, or collision extended star domain, is allowed to transmit the data. •MAC, with LLC, comprises logical ring the IEEE version of the OSI topology and a Layer 2 physical star topology •There are two broad categories of Media Access Control, deterministic (taking turns) and non-deterministic logical ring (first come, first served) topology and physical dual-ring topology Học viện mạng Bach Khoa - Website: www.bkacad.com 4
CSMA/CD • CSMA/CD used with Ethernet performs three functions: listen-before-transmit 1. Transmitting and receiving data packets 2. Decoding data packets and checking them for Transmitting& valid addresses before listening. 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 5
CSMA/CD Học viện mạng Bach Khoa - Website: www.bkacad.com 6
Backoff •After a collision occurs and all stations allow the cable to become idle (each waits the full inter-frame spacing) •The stations that collided must wait an additional and potentially progressively longer period of time before attempting to retransmit the collided frame •The waiting period is intentionally designed to be random •If the MAC layer is unable to send the frame after 16 attempts, it gives up and generates an error to the network layer Học viện mạng Bach Khoa - Website: www.bkacad.com 7
Extra: Backoff • The stations involved in transmitting frames at the time of the collision must then reschedule their frames for retransmission. The transmitting stations do this by generating a period of time to wait before retransmission, which is based on a random number chosen by each station and used in that station's backoff calculations. • k= min(n,10) ; n= the number of transmission attempts • 0
Ethernet Slot Time Học viện mạng Bach Khoa - Website: www.bkacad.com 9
Ethernet Slot Time Học viện mạng Bach Khoa - Website: www.bkacad.com 10
Ethernet Communications Học viện mạng Bach Khoa - Website: www.bkacad.com 11
Remind Học viện mạng Bach Khoa - Website: www.bkacad.com 12
Ethernet frame structure •At the data link layer the frame structure is nearly identical for all speeds of Ethernet from 10 Mbps to 10,000 Mbps •At the physical layer almost all versions of Ethernet are substantially different from one another with each speed having a distinct set of architecture design rules •The Ethernet II Type field is incorporated into the current 802.3 frame definition. The receiving node must determine which higher-layer protocol is present in an incoming frame by examining the Length/Type field Học viện mạng Bach Khoa - Website: www.bkacad.com 13
Ethernet frame structure •The Preamble is used for Synchronization, Address types timing synchronization in the asynchronous 10 Mbps and slower implementations of 10101011 Ethernet. Faster versions of Ethernet are synchronous, and this timing information is redundant but retained for compatibility •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) Học viện mạng Bach Khoa - Website: www.bkacad.com 14
Ethernet frame structure •The type value specifies the Length if value < 1536 decimal, upper-layer protocol to (0x600) need LLC to identify receive the data after upper protocol 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) •The maximum transmission unit (MTU) for Ethernet is 1500 octets, so the data should not exceed that size 4 bytes •Ethernet requires that the CRC frame be not less than 46 Type if value => 1536 decimal, octets or more than 1518 (0x600) it identify upper octets (Pad is required if not protocol enough data) Học viện mạng Bach Khoa - Website: www.bkacad.com 15
Naming on Ethernet MAC ADDRESS •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 Học viện mạng Bach Khoa - Website: www.bkacad.com 16
OUI Học viện mạng Bach Khoa - Website: www.bkacad.com 17
Ethernet in full duplex Full-duplex Full-duplex Collision occurs only in half-duplex Full-duplex Full-duplex • If the attached station is operating in full duplex then the station may send and receive simultaneously and collisions should not occur. • Full-duplex operation also changes the timing considerations and eliminates the concept of slot time • In half-duplex, if no collision, the sending station will transmit 64 bits (timing synchronization) preamble, DA, SA, certain other header information, actual data payload, FCS Học viện mạng Bach Khoa - Website: www.bkacad.com 18
Ethernet in full duplex Học viện mạng Bach Khoa - Website: www.bkacad.com 19
Ethernet in full duplex Học viện mạng Bach Khoa - Website: www.bkacad.com 20