NRS1 Module 3 Flashcards
What are the functions of the Link layer?
Required as an interface between the underlying physical infrastructure and the upper layers; it hides the details ofthe interaction with the physical medium entirely from the upper-layer protocols so that they do not need to haveknowledge of the underlying physical infrastructure.More specifically, the Link layer is in change of encapsulation of upper-layer data, unique addressing of physicalinterfaces into the local network, and orderly access of devices to use the physical medium.
What are the characteristics of Ethernet?
Ethernet was originally designed as a broadcast technology that relied on a shared media for communication. It useda “passive” wait-and-listen protocol called CSMA/CD to handle frame collision on a shared media. It has evolved toallow collision-free transmission on point-to-point interfaces.It uses MAC addresses to identify devices on the network.It uses a frame format that includes source and destination MAC addresses, the type of information being carried, theupper-layer payload, and a frame-check field to detect transmission errors.
What is CSMA/CD and why does it result in half duplex operation?
In CSMA/CD all hosts constantly listen to the shared media. When a host transmits, all other hosts listen to the sendinghost and do not transmit. All hosts receive frames from the sending host.CSMA/CD is a protocol used reduce the chance of collision and handle those that occur, but it does not and cannotprevent them. When two hosts transmit frames at the same time, they will both detect collision. Both hosts willgenerate a jam signal to notify all other hosts. A random back-off timer is then started on the two transmitting hosts.Afterward, either of the hosts will initiate a transmission after they detect no other transmission on the line.As a result, only one host can successfully transmit at a time, resulting in half-duplex operation
What are the differences between an Ethernet switch and an Ethernet hub?
An Ethernet switch can provide full-duplex capabilities on point-to-point interfaces. An Ethernet switch can make anintelligent forwarding decision and send frames only to the port that needs to receive them.The hub, on the other hand, provides half-duplex capabilities and collisions can occur. Any Ethernet frame that arriveson a port is automatically forwarded out to all other ports.
When does an Ethernet switch record a MAC address in its MAC FDB?
When an Ethernet switch receives an Ethernet frame, it records the source MAC address and the interface on which itarrived to its MAC forwarding table (FDB)
Differentiate between a collision domain and a broadcast domain
A collision domain is one in which two or more endpoints (hosts or switches) are connected to each other eitherdirectly or through one or multiple hubs. If there are hubs in between, collisions can occur, and CSMA/CD ismandatory. If it is only two endpoints and there is no hub in between, collisions can still occur if redundant cabling hasnot been installed. It is called a collision domain because of the possibility of collisions among its connected endpoints.In a broadcast domain, every Ethernet device will receive and process all broadcast packets.
What are the advantages of using VLANs in an Ethernet network?
1) To decrease the amount of broadcast traffic – broadcast traffic from a device within a VLAN is only received andprocessed by other devices within the same VLAN. Devices in a different VLAN do not process that traffic.2) To increase the network security – traffic in one VLAN is separated from that in another VLAN as if they wereseparate physical networks.
What are the benefits of VLAN stacking?
1) It solves the problem caused by Provider Edge (PE) routers only supporting 4,094 VLANs.2) It allows multiple customers to use the same VLAN tag values in their networks
What are the benefits of a LAG?
A LAG is used to provide link redundancy. A LAG aggregates multiple physical links between Ethernet devices so thatthey are functionally equivalent to a single logical link.The primary benefits of a LAG are:1) It increases the bandwidth available between two Ethernet devices by grouping multiple ports into one logical link.2) It provides link redundancy between devices.
What problems can be encountered in a switched network with path redundancy if STP is not used?
1) Broadcast storm due to constant “looping” of Ethernet frames.2) FDB table instability as switches might see a frame with a source address that comes from a different port than theone registered in the existing entry of the MAC FDB
