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DSST Computing and IT study materials
DSST Computing and IT study resources

DSST Computing and IT: Connectivity: Networks, Addressing, and Troubleshooting

DSST Computing and IT · Work through your exam, one topic at a time.

All guide sections

Connectivity: Networks, Addressing, and Troubleshooting

Connectivity covers how devices reach each other and the internet, and how faults are isolated. The exam tests layered models, device roles, addressing, and the order of troubleshooting steps. Expect scenario questions where a host cannot reach a service and you must identify the failing layer or service.

Layered models

  • The OSI reference model has seven layers: physical, data link, network, transport, session, presentation, application.
  • TCP/IP condenses these into network access, internet, transport, and application layers.
  • Each layer serves the one above it; a fault at a lower layer breaks everything above.

Devices and media

  • Hubs repeat signals to all ports at layer 1; switches forward frames by MAC address at layer 2; routers forward packets by IP address at layer 3.
  • Firewalls filter traffic by rules; gateways translate between dissimilar systems.
  • Ethernet is the dominant wired LAN standard; Wi-Fi uses shared radio channels and CSMA/CA.

Addressing and services

  • IPv4 addresses are 32-bit; private ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16, translated by NAT for internet access.
  • DHCP assigns addresses, masks, gateways, and DNS servers automatically.
  • DNS resolves names to addresses; a default gateway routes traffic off the local subnet.
  • TCP is connection-oriented and reliable; UDP is connectionless and faster, suiting voice and video.

Performance concepts

  • Bandwidth is capacity; latency is delay. High bandwidth does not fix high latency.
  • A VPN encrypts traffic over an untrusted network; it does not guarantee speed.

Worked example

A workstation reports address 169.254.23.10 and cannot reach any website. Reasoning: 169.254.x.x is an APIPA self-assigned address, meaning the host never received a DHCP lease. The first check is link status and the DHCP server or relay, not DNS and not the web server. Once a valid lease with gateway and DNS settings appears, retest name resolution. If other hosts on the same switch work normally, the fault is local to this host or its cable and port.

Traps that cost marks

  • Confusing switches with routers, or claiming a hub filters traffic.
  • Choosing TCP for real-time voice, or UDP for file transfer requiring reliability.
  • Blaming DNS when the host has no valid IP address at all.
  • Forgetting that private addresses are not routable on the public internet without NAT.
  • Treating bandwidth and latency as the same measure.