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BCCITB: Networking and Internet Technologies

BCCITB · Work through your exam, one topic at a time.

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Networking and Internet Technologies

This domain checks whether you can explain how data moves between hosts, and diagnose a break in that path layer by layer rather than guessing.

Core rules

  • Layers - OSI's seven layers teach the model; TCP/IP's four layers describe practice. Each layer adds or strips its own header.
  • Addressing - private ranges are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. An address starting 169.254 is APIPA, meaning no DHCP server answered.
  • Services - DHCP uses DORA (Discover, Offer, Request, Acknowledge). DNS resolves names to addresses. NAT translates private addresses to a public one.
  • TCP vs UDP - TCP handshakes and retransmits, so it suits web and file transfer. UDP is connectionless and low-latency, suiting DNS queries, VoIP and video.
  • Ports worth memorising - 22 SSH, 25 SMTP, 53 DNS, 80 HTTP, 443 HTTPS, 3389 RDP.
  • Mask and gateway - the subnet mask defines local scope; the default gateway is the router used for everything off-subnet.

Worked example

A workstation reports 169.254.12.7 and reaches nothing, including the gateway. Reasoning: APIPA rules out DNS, because the host never obtained an address at all. Work the DHCP chain - cable or Wi-Fi association, switch port, VLAN, DHCP scope exhaustion - before touching DNS settings.

Traps that cost marks

  • Ping by name succeeds but ping by IP fails: that is name resolution, not connectivity.
  • Confusing the default gateway with the DNS server; they are separate roles.
  • Treating port 443 as proof a site is trustworthy - it proves encryption only.
  • Reporting "the internet is down" when one site or one service has failed.