Basic Networking

Basic Networking Concepts

- Protocols - Protocols are sets of rules that devices use to communicate with each other for different purposes. They can function at one or several layers of the OSI model, and can call on other protocols to perform services. For example, HTTP is an application layer protocol that defines how web browsers and web servers communicate, and it also uses TCP protocol at the transport layer to provide a reliable transfer of data. Ethernet can refer to both ethernet wiring, and how the data on those wires is formatted for sending to particular hosts on the same LAN. TCP/IP refers to a suite of protocols that most networked devices commonly use for communication between LANs.

- OSI and TCP/IP Models -

- Layers

- Data Encapsulation - The protocols used to move data from one host to another on a LAN, between LANs, and finally to a particular program on the machine on the recieving end all use layers of encapsulation. We'll start with the way data is encapsulated on a LAN. A network card takes the data it is given by the operating system, and adds a header with address information for another device on the LAN. The data, and the header that was added are together called a frame. A frame is the protocol data unit (PDU) used by ethernet. Next, within that frame is another PDU called an IP packet with its own header, and more data inside that. When that frame reaches a router, the router strips off the ethernet header, and looks at the IP header. It then chooses an interface to forward the IP packet out of based on the information in its routing table. If the other interface is an ethernet jack leading to a different LAN, it will encapsulate the packet again into a new frame with a new header.

Layer 1: Physical

Cabling

- UTP Cable - 100m range, TIA/EIA568a and b pinouts, EMI, plenum vs. regular PVC

- Fiber Optic

- Installation and Troubleshooting - crimping, patch panels, cable testing tools

Layer 1 Devices

- Repeaters

- Hubs

Layer 2: Data Link

Ethernet Protocol - MAC addresses, LLC and MAC sublayers, ethernet frame structure, header and footer.

Layer 2 Devices

- Bridge

- Switch

Layer 3: IP

IPv4 - IP address structure, classless vs. classful

IPv6

IPv4 Subnetting

Routing basics

Related services/protocols: DHCP, DNS, ARP, ICMP

Layer 4: Transport

TCP vs. UDP

Ports, sockets

NAT and port forwarding

Common port numbers for protocols

Application Layer:

Common protocols, FTP, HTTP, SSH, HTTPS, POP3, SMTP, IMAP4, etc.