Networking: Basics

Overview

Networking

Overview

The internet connects various computing devices globally. When accessing a website from a smartphone or laptop, the connection typically goes through a cellular tower, a router, and then to Internet Service Providers (ISPs). Packets are forwarded through local ISPs to the network hosting the website. Within the company network, packets pass through a link-layer switch to reach the appropriate server.

Routers and link-layer switches are both packet switches responsible for forwarding packets. Routers are primarily used in the network core to connect multiple networks, while link-layer switches are utilized in access networks to connect multiple devices within a single network.

Computer Networking: Top-Down Approach

DNS

Domain Name System (DNS) is a decentralized naming system for computers, services, or any resource connected to the Internet or a private network. It translates human-readable domain names (like example.com) into IP addresses (like 192.0.2.1), which computers use to identify each other on the network.

DNS Server Types

• Authoritative: Stores DNS records for a domain and provides answers to DNS queries about that domain
• Recursive (Resolver): Receives DNS queries from clients and fetches the corresponding DNS records by querying other DNS servers
• Root: First step in resolving a DNS query. It points to the authoritative servers for top-level domains (TLDs) like .com, .org

DNS Record Types

• A (Address) Record: Maps a domain name to an IPv4 address
• AAAA (IPv6 Address) Record: Maps a domain name to an IPv6 address
• CNAME (Canonical Name) Record: Alias of one domain to another (www.example.com to example.com)
• MX (Mail Exchange) Record: Specifies the mail server responsible for receiving email on behalf of the domain
• TXT (Text) Record: Used to associate arbitrary text with a domain. Often used for SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) records
• NS (Name Server) Record: Specifies the authoritative name servers for the domain
• SOA (Start of Authority) Record: Contains administrative information about the domain name, such as the primary name server and the email of the domain administrator

DNS Resolution for Web Browsing

Process of DNS Resolving IP

CDN Process

OSI Model

OSI (Open Systems Interconnection) model is a conceptual framework used to understand and standardize the functions of a telecommunication or computing system.

OSI Model Layer	Visualization	Description	Protocols	Data Format	TCP/IP Model
Application Layer		Closest to end users; where most applications reside. Requests data from backend servers without needing to understand data transmission specifics	DNS, HTTP, SMTP, FTP	Sending Data	Application Layer
Presentation Layer		Handles data encoding, encryption, and compression for the application layer and prepares data for transmission, such as HTTPS using TLS for secure communications	TLS, SSL
Session Layer		Manages opening and closing of communications between devices and sets checkpoints for large data to avoid full retransmission from the beginning	Sockets
Transport Layer		Manages end-to-end communication between devices. Breaks data into segments at sender's side and reassembles at receiver's side. Implements flow control to prevent congestion	TCP, UDP	Sending Segments, Datagrams	Transport Layer
Network Layer (IP logical addressing)		Facilitates data transfer between different networks. Divides segments or datagrams into smaller packets. Finds optimal route to destination using IP addresses (routing)	IP, ICMP, IGMP, IPsec	Sending Packets	Internet Layer
Data Link Layer (MAC physical addressing)		Allows data transfer between devices on the same network. Breaks packets into frames confined to local area network	Ethernet, WiFi	Sending Frames	Network Address Layer
Physical Layer (cables)		Sends bitstreams over cables and switches. Closely associated with physical connection between devices	Fiber	Sending Bits

Transfer Process

Linux Kernel