Networking and Connectivity
Core concepts
Know the OSI and TCP/IP models and map protocols to layers: Ethernet at the link layer, IP at the network layer, TCP/UDP at transport, HTTP/DNS/DHCP at application. Understand IPv4 addressing, subnet masks, default gateways, private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), NAT, and basic IPv6. Distinguish LAN, WAN, VLAN, and VPN. Know DNS resolution, DHCP lease process, and common ports (HTTP 80, HTTPS 443, DNS 53, DHCP 67/68, SSH 22). Understand switching vs routing, Wi-Fi standards, and cabling categories.
Traps in questions
A classic trap is confusing a switch (same subnet, MAC-based) with a router (between subnets, IP-based). Another is assuming DNS assigns IP addresses - DHCP does; DNS resolves names. Do not confuse TCP (connection-oriented, reliable) with UDP (connectionless). Watch for questions that place a protocol on the wrong layer. Also, a device with an IP but no gateway can reach local hosts but not the internet, and APIPA addresses (169.254.x.x) signal DHCP failure.
Worked example / rule of thumb
A host reaches local servers but not websites. Rule of thumb: local works, remote fails - suspect the default gateway or DNS. Check the gateway address and ping it; then test name resolution by pinging a public IP versus a hostname. If the IP works but the name fails, DNS is the issue; if neither works, the gateway or routing is at fault.
Exam focus
Expect subnetting basics, protocol-to-layer mapping, port numbers, and troubleshooting by isolating which layer fails.