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Wrap-up and resources

Key Takeaways

1. What is a network? Devices, kinds and measures: A network is devices, links and rules. The internet is a network of networks, every device works at a given layer, and speed is one thing while delay is another.
2. Layers: the OSI and TCP/IP models and encapsulation: Each layer does one job and adds its header. Know which layer broke and you have done half the troubleshooting.
3. Cables and the physical layer: copper, fibre and Ethernet: The physical layer only carries bits, yet many faults start there. Know each cable's limits (100 m for copper), pick fibre for distance and speed, and start any troubleshooting with the light and the cable.
4. Addresses: IP, MAC, ARP and IPv6: MAC is for the hop inside a network, IP for the whole trip, and ARP translates between them. Private addresses never reach the internet except through NAT.

Term	Definition	Part
Network	Devices and links exchanging data by agreed protocols.	1
Protocol	Written rules both sides agree on: the shape and order of messages.	1
LAN and WAN	A local network in a building, and a wide one joining cities and countries.	1
Encapsulation	Each layer wraps its header around what the layer above handed it.	2
PDU	Data, then segment, packet, frame, bits.	2
Layer 2	Data link: MAC, frames, switches, VLANs.	2
Layer 1	Moves bits as a signal: electricity, light or radio. Knows no addresses.	3
UTP and RJ45	Copper cable with four twisted pairs and an eight-pin connector.	3
Copper limit	100 m per channel: 90 fixed + patch cords.	3
MAC	A fixed 48-bit address in the network card, for layer 2.	4
IPv4	32 bits in four octets, a network part and a host part.	4
RFC 1918	The private ranges: 10/8, 172.16/12, 192.168/16.	4

Grouped by type. Start with the official docs for precision, or an article or video for the explanation.