DCNSA Level II
Computer Networking flashcards
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Complete Flashcard Reference
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Name the layers of the OSI model and of the TCP/IP model, and how they map.
OSI, 7 layers: Physical, Data Link, Network, Transport, Session, Presentation, Application. Mainly a teaching and troubleshooting reference. TCP/IP, 4 layers: Network Access, Internet, Transport, Application. The practical model the internet is built on. Network Access covers OSI's Physical and Data Link; Application covers OSI's Session, Presentation and Application.
How many usable host addresses does a subnet have, and why subtract two?
Usable hosts = 2^h - 2, where h is the number of host bits left after the network prefix. The first address in the block is the network address and the last is the broadcast address; neither can be assigned to a device. Example: a /26 has 6 host bits, 64 addresses, 62 usable.
What is the difference between a switch and a router?
Switch: directs traffic within one network, learning which device sits on which port from its MAC address. Works at the Data Link layer. Router: directs data between different networks, such as a LAN and the internet, forwarding by IP address. Works at the Network layer.
Compare UTP, STP and fibre optic cable on cost, interference resistance and typical use.
UTP: low cost, moderate interference resistance, the standard office LAN cable (1 Gbps to 100 m). STP: moderate cost, high interference resistance, for high-interference sites such as near industrial machinery. Fibre optic: high cost, immune to electrical interference, 10 Gbps or more over kilometres, for backbones and inter-building links.
Why is the star the dominant modern LAN topology, and what is its weakness?
Every device connects to a central hub or switch, so a single device or cable failure affects only that device, and it is the easiest topology to troubleshoot: check one cable run back to its port. Weakness: the whole network depends on the central device, a single point of failure.
A device has an address in the 169.254.x.x range. What does it mean, and what do you check first?
It is an APIPA (Automatic Private IP Addressing) address: the device could not reach a DHCP server and assigned itself a fallback address. Check DHCP first: the DHCP server and the device's connection to it (cable, switch port, the DHCP service itself), not the device's own settings.
How do TCP and UDP differ, and what is each used for?
TCP: connection-oriented, reliable, ordered delivery with retransmission of lost data. Used where accuracy matters: web browsing, file transfer, email. UDP: connectionless, faster, no delivery guarantee and no retransmission. Used where speed matters more than occasional loss: video streaming, voice calls, online gaming.
What does each layer of the hierarchical network design model do?
Core: the high-speed backbone between distribution blocks, doing as little processing as possible so it never bottlenecks. Distribution: enforces policy and routing between access and core, such as access control lists and routing between subnets, and aggregates access switches. Access: where end devices (computers, printers, phones) connect, through edge switches.
Distinguish guided from unguided transmission media.
Guided (wired): signals follow a physical path, copper or fibre. Higher, more predictable speed and less exposure to interception, but cabling must reach every device. Unguided (wireless): signals travel through the air as radio, microwave or infrared. No cabling and supports mobility, but shared, more congested bandwidth and more exposure to interference and eavesdropping.
How do you work out the downtime an availability target allows in a year?
Downtime per year = (1 - availability) x 525,600 minutes (365 x 24 x 60). 99%: 5,256 minutes. 99.9%: 525.6 minutes. 99.99%: 52.56 minutes. Each extra nine cuts the allowance by ten, which is why it gets disproportionately expensive.
What is the difference between data and information?
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What are the benefits of using computers on a network rather than standalone?
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What safety precautions apply when working on shared networking equipment?
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What is the role of a network card (NIC), and why does it need a driver?
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What physical ports does networking hardware carry?
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What counts as networking software? Give examples.
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How does CSMA/CD control access to a shared medium?
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How do token passing and polling control access to the medium?
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What is coaxial cable, and where is it still used?
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List the network types by scope, smallest to largest.
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What is a storage-area network (SAN), and why use one?
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What is the difference between physical and logical topology?
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What are the strengths and weaknesses of bus and ring topologies?
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When is a mesh topology the right choice, and what does it cost?
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What is a hybrid topology?
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Distinguish an intranet, an extranet and the internet by who can reach them.
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Is the World Wide Web the same thing as the internet?
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What do a hub and a bridge do, and why have switches replaced hubs?
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What is a node, and what is a server?
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What are the core functions of a computer network?
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How do IPv4 and IPv6 addresses differ?
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What are the private IPv4 ranges, and how does a private address differ from a public one?
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Distinguish unicast, broadcast and multicast.
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What is subnetting, and what does it achieve?
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Split 192.168.1.0/24 into four equal subnets.
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What is VLSM, and in what order are subnets allocated?
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What three steps work any subnetting or VLSM question?
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What do routing algorithms do, and what metrics do they use?
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State the port numbers for HTTP, HTTPS, FTP, SMTP, POP3 and IMAP.
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How does POP3 differ from IMAP?
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Distinguish availability from manageability as design qualities.
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What are the five standard elements of a network design sketch?
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Contrast modular and flat network design.
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What is the enterprise edge?
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What six requirements is a network design judged against?
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What problem does quality of service (QoS) solve?
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Why are network design tools used before a network is built?
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How to revise with these cards
- Answer out loud or on paper before you turn the card: recalling is what fixes it.
- Go through the deck in short sessions of ten to fifteen minutes, every day.
- Shuffle once you know the order, so you are not answering from memory of the sequence.
- When a card catches you out, read the chapter it links to, then try the topic in a past paper.