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NETW202 Ch 9
Ethernet
| Question | Answer |
|---|---|
| ARP cache | A logical storage in a host's RAM to store ARP entries. |
| ARP poisoning/spoofing | A technique used to attack an Ethernet network by sending fake ARP messages to an Ethernet LAN. These frames contain false MAC addresses that "confuse" network devices and cause frames intended for one node to be sent to another node. |
| ARP table | A logical storage in a host's RAM to store ARP entries. |
| asynchronous | Communication that does not use a common clock between the sender and receiver.To maintain timing, additional information is sent to synchronize the receive circuit to the incoming data. |
| bridge table | The table used by a switch or bridge that associates MAC addresses with the outgoing port. The switch or bridge uses this table for its forwarding/filtering decisions. |
| bridge | A device that connects multiple network segments at the data link layer of the OSI model. Predecessor to switches. |
| bridging | The process of forwarding frames in a switch or a bridge from one port to another port or from segment to segment. |
| burned-in address (BIA) | The MAC address that is permanently assigned to a LAN interface or NIC. it is called burned-in because the address is burned into a chip on the card, and the address cannot be changed. Also known as a universally administered address (UAA) |
| carrier sense multiple access collision detect (CSMA/CD) | The MAC algorithm used by Ethernet devices in a shared media. A node wishing to transmit will listen for a carrier signal before trying to send. |
| collision domain | A physical or logical area in a LAN where the signals sent by the interfaces (including NICs) may be subject to being combined (a collision). |
| delimiter | This field of a frame signals the beginning or the end of a frame. |
| Ethernet PHY | The physical interface transceivers. It deals with the Layer 1 (the physical layer, hence the PHY) of Ethernet. |
| extended star | A network topology characterized by a central location connected to multiple hubs. In an extended star, these interconnected hubs may be connected to more hubs. Sometimes called a hierarchical star. |
| fast ethernet | A common name for Ethernet technology that operates at 100 Mbps. |
| filtering | In Ethernet, the process performed by a bridge or switch when it decides that it should not forward a frame out another port. |
| flooding | A process used by a switch or bridge to forward broadcasts and unknown destination unicasts. The bridge/switch forwards these frames out all ports except for the port on which the frame was received. |
| forwarding | In Ethernet, the process performed by a bridge/switch when it decides that it should send a frame out another port. |
| gigabit Ethernet | Ethernet that transmits data at 1,000,000,000 (1 billion) bits per second. |
| host group | A group defined by a class D address (multicast 224.0.0.0 to 239.255.255.255), whereupon hosts can pertain to multicast groups. Hosts that have the same multicast address are part of the same host group. |
| hub | A Layer 1 device that receives an electrical signal in one port, interprets the bits, and regenerates a clean signal that is sends out to all other ports of the hub. |
| interframe spacing | Time period between Ethernet frames that allows fairness with the CSMA/CD algorithm. W/o a space between frames,a NIC might always listen for silence, never hear silence, and therefore never get a chance to send a frame. |
| jam signal | A shared Ethernet network signal generated by the transmitting device that detects the collision. It will continue to transmit for a specific period to ensure that all devices on the network detect the collision. The jam signal is a part of CSMA/CD. |
| latency | The time that passes while some event occurs. Latency refers to the time that occurs between when something is sent in a network until it is received by another device. |
| locally administered address (LAA) | A MAC address that can be configured on a device. The LAA can be used in place of the BIA. This means that you can replace a NIC or use a substitute device without changing the address used by the network to access the station. |
| MAC table | On a switch, a table that lists all known MAC addresses, and the bridge/switch port out which the bridge/switch should forward frames sent to each MAC address. |
| metropolitan-ara network (MAN) | A network with a geographic size between a LAN and a WAN. Typically used by service providers to create a high-speed network in a major metropolitan area where many customers might want high-speed services between large sites around the city. |
| organization unique identifier (OUI) | The first half of a MAC address. Manufacturers must ensure that the value of the OUI has been registered with the IEEE. This value identifies the manufacturer of any Ethernet NIC or interface. |
| pad | A part of the Ethernet frame that fills in the data field to ensure that the data field meets the minimum size requirement of 46 bytes. |
| proxy ARP | Process that uses the same ARP msgs as normal ARP, but by which a router replies instead of the requested host since the ARP request can't reach the requested host. |
| pulse amplitude modulation (PAM) | Form of signal modification where the message info is encoded in the amplitude of a series of signal pulses. It transmits data by varying the amplitudes of the individual pulses. This is now obsolete and has been replaced by pulse code modulation. |
| random-access memory (RAM) | read-write memory. Main working area, or temporary storage, used by the CPU for most processing and operations. Volatile and will be lost if the device is turned off. |
| read-only memory (ROM) | A type of computer memory in which data has been prerecorded. After data has been written to a ROM chip, it cannot be removed and can only be read. |
| runt frames | An Ethernet frame that is less than 64 bytes in size (which is the min. frame size for Ethernet). Runts are caused by collisions and are also known as collision fragments. |
| selective forwarding | The forwarding of packets where the forwarding decision is taken dynamically, hop by hop, based on the conditions of downstream and forwarding nodes. |
| slot time | The min. time a NIC or interface can take to send an entire frame. Slot time, then, implies a min. frame size. |
| store and forward | A method of internal processing by LAN switches. The switch must receive the entire frame before it sends the first bit of the frame. Store-and-forward switching is the method used by Cisco switches. |
| switch table | A general term for the table that a LAN bridge uses for its forwarding/filtering decisions. The table holds a list of MAC addresses and the port out which the bridge should forward frames for those frames to reach the correct destination. |
| synchronous | Communication that uses a common clocking signal. In most synchronous communication, one of the communication devices generates a clock signal into the circuit. Additional timing information is not required in the header. |
| thicknet | A common term for 10BASE5 Ethernet, referring to the fact that 10BASE5 cabling is thicker than the coaxial cabling used for 10BASE2 (Thinnet). |
| thinnet | A common term for 10BASE2 Ethernet, referring to the fact 10BASE2 cabling is thinner than coaxial cabling used for 10BASE5 (Thicknet). |
| transparent bridging | The learning of source addresses on incoming frames and adding them to the bridging table. After the table has been completed and when a frame is received on one of the bridges interfaces and the frame is forwarded out the indicated port. |
| universally administered address (UAA) | Same thing as a burned in address (BIA) |
| virtual local-area network (VLAN) | A network of computers that behave as if they are connected to the same network segment, even though they might be physically located on different segments of a LAN. VLANs are config'd thru software on the switch and router. |
| Voice over IP (VoIP) | Voice data encapsulated in an IP packet that allows it to traverse already implemented IP networks w/o needing its own network infrastructure. |
| Name the two data link sublayers, and list their purposes. | LLC: Handles the communication between the upper layers and the lower layers, typically hardware. MAC: Ethernet MAC sublayer handles Data encapsulation, Media access control, and Addressing. |
| Which of the following describes legacy Ethernet technologies? Poor scalability, Expensive media, No collisions, or Frame format incompatible with current Ethernet? | Poor scalability |
| Which field of an Ethernet frame is used for error detection? | Frame Check Sequence |
| How many bits are in an Ethernet MAC address? | 48 |
| Why are Layer 2 MAC addresses necessary? | An Ethernet MAC address is used to transport the frame across the media. |
| Which address is used as a destination address for an Ethernet broadcast frame? 0.0.0.0. 255.255.255.255, FF-FF-FF-FF-FF-FF, or 0C-FA-94-24-EF-00? | FF-FF-FF-FF-FF-FF |
| What is the purpose of a jam signal in CSMA/CD? | To make sure that all sending nodes see the collision. |
| Describe an Ethernet collision domain. | The group of connected devices that can cause collisions to occur with each other is a collision domain. Collision domains occur at Layer 1 of the networking reference model. |
| What Ethernet characteristic is shared by historic Ethernet and legacy Ethernet? | They both share the same logical topology. |
| What is a characteristic of a connection to a switch port? | It is a separate collision domain. |
| What is the stage of operation of an Ethernet switch that creates MAC table entries? | Learning; When a frame of data is received from a node, the switch reads the source MAC address and saves the address to the lookup table against the incoming interface. |
| When does a network host need to broadcast an ARP request? | When it has a packet to send to an IP address that does not have a map in the ARP cache. |
| If a frame arrives at a switch that contains a destination MAC address that is not listed in the MAC table, what process will occur? | Flooding; When the switch does not have a destination MAC address in its lookup table, it sends (floods) the frame out all interfaces except the one on which the frame arrived. |
| Why are higher-speed Ethernet implementations more susceptible to noise? | Timing can be more easily distorted with the shorter bit times. |
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