Standards and Concepts
Domain 1 of CCST Networking tests the vocabulary and models that everything else sits on: the OSI and TCP/IP models, encapsulation, standards bodies, protocol behavior, and the basic ways networks are described. Expect questions that ask you to place a protocol or device at the correct layer and to follow a packet from application to wire.
Models and encapsulation
The OSI model has seven layers: Physical, Data Link, Network, Transport, Session, Presentation, Application. The TCP/IP model collapses these into Network Access, Internet, Transport, and Application. Each layer adds a header (and sometimes a trailer) as data moves down the stack; the unit changes name: data, segment (TCP) or datagram (UDP), packet, frame, bits. Switches operate at Layer 2, routers at Layer 3, and hubs/repeaters at Layer 1.
Standards and protocol facts
IEEE defines 802.3 Ethernet and 802.11 wireless LAN. IETF publishes TCP/IP RFCs. ISO/IEC defines OSI; TIA/EIA defines cabling standards such as TIA-568. TCP is connection-oriented and reliable; UDP is connectionless. Common ports: HTTP 80, HTTPS 443, DNS 53, DHCP 67/68, SSH 22, Telnet 23, SMTP 25, FTP 20/21. A MAC address is 48 bits; IPv4 is 32 bits; IPv6 is 128 bits.
Worked example
A laptop requests https://example.com. The browser uses HTTPS, so the transport header is TCP with destination port 443. The network header is IPv4 or IPv6 with the server's address. The data-link header is Ethernet with the next-hop MAC address, not the server's MAC if a router sits between them. The frame becomes bits on the medium. At the server the process reverses.
Traps
Do not confuse PDU names: TCP data is a segment, IP data is a packet, Ethernet data is a frame. A switch does not normally rewrite IP addresses. TCP port 53 is DNS, but DNS also uses UDP 53 for most queries. Encapsulation adds headers at each layer; de-encapsulation removes them.