A network connects interfaces so applications on different hosts can exchange data. Understanding which device, address, and link handles each part of the path makes later Linux commands easier to interpret.
Network Basics · Lesson 1
Network Basics
Learn how hosts, links, switches, routers, and packets form local and wide-area networks.
Hosts and Interfaces
A host is an endpoint or networked system, such as a laptop, server, phone, or virtual machine. One host can have several interfaces: Ethernet, Wi-Fi, loopback, tunnels, bridges, or virtual adapters. Each interface can have link-layer and network-layer configuration appropriate to its technology.
Inspect a Linux host's interfaces and addresses with:
$ ip address show
An interface being present or administratively up does not prove end-to-end connectivity.
What is a network interface?
Local Networks
A local area network, or LAN, covers a limited environment such as a home, office, or data center segment. Ethernet switches forward frames between ports on a local link. A wireless LAN, or WLAN, uses wireless link technology. Wired and wireless interfaces can still belong to the same IP subnet when a bridge or access point joins them.
How does a WLAN relate to a LAN?
Routers and Wider Networks
A router forwards network-layer packets between IP networks according to its routing table. A home device often combines routing, switching, Wi-Fi access, firewalling, NAT, and DHCP, but those remain distinct functions.
A wide area network, or WAN, spans larger geographic or administrative boundaries. An Internet service provider can connect a customer network to other networks, but “WAN” does not simply mean every device outside one house.
What is a router's defining role?
Packets, Frames, and Flows
Applications produce data that protocol layers divide and encapsulate for transmission. IP carries packets across networks; a local link carries each packet inside a technology-specific frame. Routers normally replace link-layer framing at each hop while forwarding the IP packet onward.
A conversation can involve many packets in both directions. Loss, reordering, fragmentation, retransmission, and path changes mean one captured packet rarely describes the whole application transaction.
What normally happens to link-layer framing at a router hop?
Lesson complete
You finished Network Basics
You can now describe the main components of a basic network path.
Distinguish hosts from their physical and virtual interfaces.
Recognize wired and wireless forms of local networks.
Separate routing from other functions in a combined home device.
Distinguish link frames from routed IP packets.
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