ccna 200-301 network simulator ns2 serves jeep

ccna 200-301 network simulator ns2 serves jeep.A major development in Ethernet was the emergence of switches, which were used in place of hubs in Ethernet. Switches provide dedicated bandwidth to each workstation and can work in full duplex to avoid collisions. The switch is able to forward based on the port corresponding to the destination MAC address, leaving unrelated ports unaffected, thus creating a multipath Ethernet network where data can be sent simultaneously between multiple unrelated nodes; this type of communication is described as full-duplex communication.Ethernet switches use 5 basic operations to perform their functions: learning, aging, flooding, selective forwarding, and filtering.. Learning: the switch MAC address table contains the MAC address and the corresponding port. As each frame enters the switch, the switch reviews the source MAC address, performs a lookup, and if the MAC address table does not contain this MAC address, the switch creates a new entry that includes the source MAC address and the incoming port. Later, if there are frames going to this MAC address, the switch forwards them to the corresponding port.. Aging: MAC address entries in the switch have a survival time. For each MAC address entry learned, a time value is appended. As time passes, the value keeps decreasing, and when the data value decreases to 0, the MAC address entry is cleared. If a new frame containing this MAC address arrives, the MAC address aging time value is refreshed.. Flooding: If the switch receives a data frame, it can look for it in the switch's MAC address table. if the destination MAC address of the data frame is not found, the switch forwards the data frame to all ports except the receiving port, that is, it broadcasts the data frame. If the switch receives a data frame that is broadcast, i.e., the destination MAC address of the data frame is "FFFFFFFFFFFFF", the switch also forwards the data frame to all ports except the receiving port. Because no device has a MAC address of "FFFFFFFFFFFFF", the switch learns based on the source MAC address of the data frame and never learns this MAC address.. Selective forwarding:The switch forwards the frame based on the destination MAC address of the frame. When the switch receives a data frame, the switch looks up the destination MAC address of the data frame in the MAC address table, and if the switch has learned this MAC address, the data frame will be forwarded to the port corresponding to that MAC address without flooding to all ports.. Filtering: In some cases, frames will not be forwarded, a process known as frame filtering. In one case, the switch does not forward the frame to the received port; in another case, if a frame's CRC checksum fails, the frame is also discarded. Another reason for using frame filtering is security considerations, which can prevent or allow a switch to forward specific MAC addresses to specific ports.There are several factors that have made Ethernet so successful: . Simplicity and ease of maintenance; . The ease of incorporating new technologies; . Increased reliability; . Low cost of installation and upgrades.71 44. How CSMA/CD Works CSMA/CD is an acronym for CarrierSense MultipleAccess/CollisionDetection, which translates to "Carrier Sense Multiple Access/Collision Detection" or "Carrier Sense Multiple Access with Collision Detection". oCSMA/CD is a contention-based media access control protocol. It originated from the contention protocol used in the ALOHA network developed by the University of Hawaii, USA, and has been improved to provide higher media utilization than the ALOHA protocol. CSMA/CD is a distributed medium access control protocol in which each station (node) in the network can independently decide on the sending and receiving of data frames. The so-called Carrier Sense, meaning that each workstation on the network before sending data are listening to the bus there is no data transmission. If there is data transmission (called bus busy), then no data is sent; if there is no data transmission (called bus empty), then the ready data is sent immediately. The so-called Multiple Access means that all workstations on the network use the same bus for sending and receiving data, and the data sent is broadcast. The so-called conflict (Collision), meaning that if there are two or more workstations on the network at the same time to send data, the collision of signals will occur on the bus, resulting in a mixture of signals, which workstation can not identify what the real data is. In order to avoid data conflicts in the process of sending, workstations in the process of sending data, but also constantly detect their own data sent, there is no conflict with the data of other workstations in the transmission process, this is the collision detection (Collision Detection). The working principle of CSMA/CD media access control method can be summarized as follows: . Listen first and talk later, while listening; . Stop talking as soon as there is a conflict; . Wait for the right moment and then talk; . Listen, i.e., listen and detect; . Listen, i.e., listen and detect; ... Speak, i.e., send data. Before sending data, listen to the bus to see if it is idle. If the bus is busy, it does not send; if the bus is idle, it sends the prepared data to the bus. In the process of sending data, the workstation checks the bus while sending to see if there is a conflict in the data it sends. If there is no conflict, it continues to send until all