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Karteikarten von Scott Jones, aktualisiert more than 1 year ago
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| Frage | Antworten |
| What is SFP | Small form-factor pluggable. They are ports used for fiber connections. |
| What interfaces are SFP/SFP+ be used on? | SFP : Gigabit interfaces SFP+ : 10Gbps interfaces |
| What is multimode fiber? | An LED emits light at multiple angles into the core. It uses a wider core than single-mode. |
| What is single-mode fiber? | A laser based transmitter send light through the core at a single angle. It uses a narrower core than multimode. |
| Why are fiber cables more secure than UTP? | UTP emits a faint signal outside the cable, the transmitted data is at risk of being intercepted. |
| What is a multicast address? | The address used by a subset of devices on the LAN that volunteer to receive data. |
| What is the MAC? | All devices are assigned a unique Media Access Control address. Specifically, the address is assigned to individual NICs. It allows them to be identified on networks for sending and receiving frames. |
| What is a broadcast address? | It is used for sending data to all devices on the Ethernet LAN. The address is FFFF:FFFF:FFFF |
| List 4 alternative names for the MAC address. | Ethernet, NIC, LAN, and Unicast address. |
| How many bytes in a MAC address? | 6-bytes |
| How many bits are in a single hex digit? | 4 bits |
| How many bits in a byte? | 8 bits in a byte |
| How are MAC addresses unique? | NIC manufacturers get a 3-byte organisationally unique identifier (OUI) from the IEEE. The OUI is used on the first half of the MAC address. For the last half the manufacturers produces their own random 3-byte value (vendor assigned). |
| What is half duplex logic? | The device must wait to send if it is receiving a frame; it cannot send and receive simultaneously. |
| What is full duplex logic? | A node does not have to wait on other devices as it can send and receive frames at the same time. |
| Acronym 'CSMA/CD' | Carrier Sense Multiple Access With Collision Detection |
| The CSMA/CD algorithm is used with LANs using what device? | Hubs |
| Should ports connecting to a LAN hub use full duplex or half duplex logic? | Half duplex |
| Why is it important to understand CSMA/CD? Why not just use full duplex logic? | Occasionally you will find hubs being used in some enterprise networks. Full duplex does not work on hubs, the CSMA/CD algorithm must be used. |
| In simple terms, what does CSMA/CD do? | It alleviates collisions by managing how devices recover from a collision and resend frames. |
| On a LAN using a hub, does everything have to use half duplex logic, or would it only be the ports directly connected to the hub? | Only the ports connected to the hub. |
| On LANs using hubs, what are collisions? | Collisions are when multiple frames collide during transmission because hubs support only 1 frame in transmission at a time. |
| What is meant by a hub flooding frames? | For data to reach its destination, the hub will simultaneously transmit frames out to all other ports. |
| What are the advantages of hub ports using half duplex logic? | It helps prevent collisions because devices must wait for the traffic to be clear before sending data. |
| What are the limitations of half duplex logic ? | Collisions still happen because when the traffic is clear, any waiting nodes will transmit at the same time. |
| Name three application layer protocols. | HTTP, POP3, SMTP |
| Name the major protocol in the network layer. | Internet Protocol (IP) |
| What are the wired and wireless protocols used in the data link layer? | Ethernet & 802.11 |
| Name two transport layer protocols. | Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) |
| Explain how a webpage gets from a server to a browser in the application layer. | The browser sends a GET request to the server. The name of the file is in the HTTP header. The server responds with an OK message and sends part of the file. Subsequently it sends more data over until all the contents of the file a received. |
| As a server responds to a request for a file, an OK message is also known as what? | code 200 |
| A server sends over the first part of the requested file to a web browser. Do the other parts of the file sent over have HTTP headers? | No, only the first part of the file. |
| Explain what TCP is and how it works. | TCP is for error recovery. If parts of the requested file are lost, TCP will send another request to send the data. |
| How do sequence numbers work with TCP? | Each part of a requested file is sent over in sequence numbers. If one of these sequences are missing, the TCP logic on the receiving side can request the data again as soon as it notices. |
| What is HTTP? | Hyper Text Transfer Protocol. It allows web browsers to request web pages and servers to send the contents. |
| What is IP and how does it work? | A network layer protocol that deals with addressing, how to group addresses, and is essential for the routing process. It places data in packets containing the destination and source address. |
| Forwarding an IP packet is also known as... | Routing |
| What is the Ethernet protocol? | It defines the Ethernet frame. The IP packet is encapsulated and the frame and its data is transmitted. When it reaches it next destination it is de-encapsulated. |
| What is 802.11 | The wireless protocol. |
| What three layers on the OSI model are considered as the application layer on the TCP/IP model. List these layers from top to bottom. | Application Presentation Session |
| What are the terminologies used when data is encapsulated at the transport, data link, and network layers | TCP Segment, IP Packet, and Ethernet Frame |
| Why is the OSI model relevant? | The numberings are still used for reference. For example, L4PDU etc. |
| What is a protocol data unit (PDU)? | It is used in OSI referencing when talking about encapsulated data at different layers. |
| An L2PDU is on what layer? | Data Link Layer |
| An L4PDU is on what layer? | Transport Layer |
| What is the IEEE? | The Institute of Electrical and Electronics Engineers. They develop communication and network standards |
| What is same layer interaction? | Two computers use a protocol to communicate with each other on the same layer. |
| What is adjacent layer interaction? | Adjacent layers on the same computer work together. |
| What do switches do? | Multiple devices will plug into a switch which will establish a LAN connection for them by plugging into a router. |
| What do routers do? | Routers connect the LAN to the WAN and |
| What does a transceiver do? | They transmit and receive data at the same time. |
| What is a node? | Networking devices that transmit and receive data. |
| What is meant by Ethernet? | A family of standards defining how to send data over cables and the protocols/rules that nodes must follow to be part of an Ethernet LAN. |
| Ethernet Frame. What does the preamble do? | Simply put, it deals with synchronisation. |
| Ethernet Frame. What does the start frame delimiter (SFD) do? | It signifies that the next byte begins the destination MAC address field. |
| Ethernet Frame: What does the Type field contain? | The type of L3PDU in the frame, typically an IP packet (IPv4 or IPv6). |
| Ethernet Frame. What does the data and padding field contain? | Data from a higher layer, typically a network layer packet. The sender adds padding to meet the minimum of 46 bytes required. |
| Data Link Layer Frames. What does the frame check sequence (FCS) field do? | It allows the receiving node to detect errors in the frame. It is the only field in the Ethernet trailer. |
| How does the frame check sequence (FCS) work? | The sender and receiver apply a math formula to the frame, if the receiver does not get the same result as the sender, it means the frame has changed during transmission, it is then discarded. |
| What is Ethernet shared media. | Also known as shared media network. Networks that use hubs, CSMA/CD and share bandwidth. |
| What is Ethernet point-to-point | A network built with switches; each (point to point) link works independently of the others. Frames can be sent on every link at the same time. |
| What are UTP cables? | Unshielded Twisted Pair. An Ethernet cable with RJ-45 connectors. The wires are twisted in two pairs or four pairs depending on the speed. |
| A UTP with two twisted wire pairs works up to what speeds? | 10BASE-T and 100BASE-T |
| A UTP cable with 4 twisted pairs works up to what speeds? | 1000BASE-T |
| What are RJ-45s? | The Ethernet ports and connectors. The connectors have 8 pin positions where the wires plug into. |
| Ethernet Frame. What is the minimum and maximum bytes in the data and padding? | 46 - 1500 |
| What is a crossover cable? | It is an Ethernet cable that swaps the pin logic on either end. Pins 1,2 on one end will connect to pins 3,6 on the other end. It is used when similar devices are connecting such as two switches or two PCs. |
| What makes a straight-through cable different from a crossover cable? | The straight-through doesn't swap the pin logic because it is used for two 'un-like' devices to connect such as a wireless AP to a switch. |
| Why does pin logic matter? | If devices trying to connect are transmitting and receiving on the same Ethernet cable pin positions, they will not connect. The device type therefore determines the cable type. |
| What does auto-mdix do? | It allows devices with Gigabit Ethernet functionality to change the cable's logic if the wrong type is used. Without Gigabit Ethernet support, a crossover cable is essential. |
| What is EMI? | Electromagnetic Interference. As electrical circuits pass over the wires, it creates interference with the signals. Twisting wires helps reduce EMI. |
| What is crosstalk? | It is when EMI takes place between different wire pairs in the same cable. |
| What does the term 'burned-in address' imply? | It's another name for the Ethernet MAC address. The MAC address is permanently encoded into the ROM chip on the NIC by the manufacturer. |
| Where is half duplex logic used? | It is used on any ports connecting to a LAN hub. |
| What is the cladding used for in fiber cables? | Reflecting light back into the core |
| What is an encoding scheme? | It is what devices use to transmit data as bits. |
| What is 'IETF' and what do they do? | The Internet Engineering Taskforce. They create new TCP/IP standards. |
| What is a telco? | A telephone company, they will create leased lines for WAN access. |
| What is the serial link on a router for? | Connecting to a leased line. |
| How do serial links transmit data? | It uses full-duplex logic with two wire pairs, one pair for each direction. |
| Were does a telco place their networking equipment? | Central Offices. |
| How does a leased line reach customers? | The telco establishes a WAN across a large area (city/country) by linking their COs. From the COs cables are installed to other buildings in preparation for selling their service. |
| What is a T1? | A specific type of leased line transmitting data at 1.544 Mbps. |
| What are 5 other names for a leased line? | Leased circuit Serial line/link, Point-to-point line/link WAN Link Private Line |
| What data-link protocols are used by leased lines? | Point-to-Point Protocol (PPP) High-Level Data Link Control (HDLC) |
| List 5 HDLC fields. | Flag, Address, Control, 'Type', FCS |
| HDLC, what is the purpose of the flag field? | It is found at the start and end of the frame. It lets nodes know that anew frame is coming and when it has ended. |
| HDLC, what is the control field? | It is not important by today's standards but it is used the process of communication. |
| HDLC, what is the address field used for? | To show where the frame is going. |
| HDLC, what makes the Type field different? | HDLC does not inherently use a Type field. Vendors need to insert their own. When the Type field is inserted, the HDLC becomes a proprietary protocol and will not work with other vendor's HDLC. |
| Why is Ethernet better than leased lines? | It is faster, cheaper, and quicker to get installed. |
| Fiber links such as 1000BASE-ZX make Ethernet a viable WAN technology. What distance does this support? | 70km |
| What is a point of presence (PoP)? | It is the local access point to an ISP. A fiber cable links the customer site to the PoP. |
| What is EoMPLS | Ethernet over Multiprotocol Label Switching - It is a technology used in creating Ethernet services. |
| Name two common names (not including EoMPLS) used for an Ethernet WAN. | Ethernet Line Service (E-Line) Ethernet Emulation |
| When transmitting frames over an Ethernet WAN, why does the destination MAC address change? | The destination MAC address relates to the next-hop router. A new MAC address is encapsulated with the frame across each point. |
| A host on a network is another name for what? | A computer |
| How do hosts choose where to send IP packets? | They use TCP/IP software embedded in their OS. |
| What is a routing table? | A table with entries to particular network destination. Routers use them for routing. |
| What is a subnet? | Part of the IP address. All devices on a LAN share the same subnet and are grouped together. When a packet contains an IP address with a different subnet it will be routed to another LAN. |
| Create IPv4 addresses for two devices on the same subnet. | The first art of the addresses should match. You should have something like: 170.83.41.55 170.83.41.113 |
| How many bytes are in an IPv4 header? | 20-bytes |
| How many bits are in the destination and source address fields in the IPv4 header? | Each are 32 bits in length |
| For a host to send packets to remote destination, what does it need to know about its own LAN? | The IP address of their default gateway. |
| What do routers need to know before they can forward packets? | The routes the packet will take. |
| What are routing protocols used for? | They enable routers to exchange routing information such as different subnets. |
| What is an internetwork? | Two or more networks connected by routers, switches, cables, and other equipment. |
| What does the routing protocol enable routers to do? | Exchange routing protocol messages and learn routes for all known IP routes. |
| What is a routing update? | A routing protocol message which tells a router's neighbours about all routes in its routing table. |
| What is DNS? | Domain Name System. It enables a computer to retrieve an IP address to connect to a server by typing the domain name. |
| What is a DNS query? | It is when a PC asks the DNS server for the IP address of the server it wants to connect to. The domain name will be sent through the DNS query. |
| What is a DNS reply? | This is when the DNS server responds to a DNS query by sending back the requested server's IP address. |
| What address is used when a router forwards a DNS message? | The IP packet will contain the DNS server's address as the destination. |
| Does a DNS server know every domain name? Explain. | No. The information is distributed across many DNS servers working together and forwarding queries to each other. |
| What is ARP? | Address resolution protocol. It enables hosts or routers to dynamically learn the MAC address of another host or router on the LAN. |
| Where do LAN devices store the MAC address of other devices? | The ARP table/cache |
| What causes the reoccurrence of ARP requests? | Devices will occasionally clean out their ARP cache. |
| What is an ARP request and how does it work? | An ARP request is when a device wants to learn the MAC address of another device. A MAC broadcast is transmitted through the LAN with the frame's IP packet containing the target destination address. The associated device will reply back with its MAC address. |
| What is an ARP reply message? | When a device receives the ARP request, it will respond with the reply message containing its IP and MAC address. |
| How would you look at the your computer's ARP cache? | Open the command terminal and type 'arp -a' |
| What is the ping command? | It is an internet control message protocol (ICMP). It sends an echo request to another IP address, if the device gives an echo reply it means packets can be delivered from one host to another and back. |
| An IP network is also known as a what? | An IP subnet. |
| What is a unicast IP address? | It is a single address, it will be the destination address in the IP packet. |
| How is an ARP message broadcasted? | The Ethernet frame needs a destination MAC address, but the whole point in an ARP request is to learn the MAC address. The message is therefore broadcasted using the broadcast address in the frame (FFFF.FFFF.FFFF) |
| On LANs using hubs, what causes collisions? | The nature of hubs flooding frames is the prime cause for this collisions. Two or more devices sending frames at the same time will cause collisions. |
| What are fiber optic cables made of? | Fiberglass, a long thing strand of flexible glass. |
| What runs along the length of a fiber cable? | A glass or plastic core. |
| What does a fiber optical transmitter do? | It shines light into the core, the light passes through the glass. |
| State the common name associated with 10Mbps | Ethernet |
| State the common name associated with 100Mbps | Fast Ethernet |
| How fast is Gigabit Ethernet? | 1000Mbps |
| 10Gbps is known by its common name as what? | 10 Gig Ethernet |
| State the formal IEEE name for 10BASE-T | 802.3 |
| State the formal IEEE name for 100BASE-T | 802.3u |
| State the formal IEEE name for 1000BASE-LX | 802.3z |
| State the formal IEEE name for 1000BASE-T | 802.3ab |
| State the formal IEEE name for 10GBASE-T | 802.3an |
| 1000BASE-LX supports a cable length of up to what? | 5000m |
| A router is sending an IP packet to a device on a local subnet, what will the router lookup as it encapsulates the packet? | The ARP table for the device's MAC address. |
| Ethernet Frame: How is the type field distinguished? | Hex numbers |
| Besides encapsulation, what does a router do with an IP packet? | It compares its destination address to its known IP routes and forwards the packet. |
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