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Networking Essentials

Networking connects computers so they can share data and access the internet. This chapter introduces the common ports and protocols, TCP/IP addressing, wireless standards, and the devices that move traffic through a network.

Common Ports and Protocols

Protocols define how devices communicate, and each service listens on a well-known port. Memorizing the frequently used ports speeds up configuration and troubleshooting.

HTTP 80, HTTPS 443

Web traffic uses port 80 unencrypted and port 443 encrypted with TLS.

SSH 22, RDP 3389

SSH provides encrypted remote CLI access; RDP provides remote desktop sessions.

Email uses SMTP 25, POP3 110, IMAP 143

SMTP sends mail between servers while POP3 and IMAP retrieve mail for clients.

Prefer encrypted protocols

SSH and HTTPS protect credentials, unlike clear-text Telnet, FTP, and HTTP.

TCP/IP and Addressing

TCP/IP is the foundation of modern networks. Devices need an IP address, subnet mask, default gateway, and DNS to communicate beyond the local segment.

Private ranges are not routable

RFC 1918 defines 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 for internal use.

APIPA signals a DHCP failure

A 169.254.x.x address means the host could not reach a DHCP server.

Subnet masks map to CIDR

255.255.255.0 equals /24, setting the first 24 bits as the network portion.

The gateway routes off-network traffic

Hosts send packets destined for other networks to the default gateway.

Wireless Standards

Wi-Fi standards define speed, frequency, and range. Technicians match the standard and band to the environment and client capabilities.

802.11ax is Wi-Fi 6

It improves efficiency and works in both 2.4 GHz and 5 GHz bands.

2.4 GHz reaches farther, 5 GHz is faster

Lower frequency penetrates walls better; higher frequency offers more speed at shorter range.

Newer standards are backward compatible

Modern access points still support older clients at reduced speeds.

Interference degrades 2.4 GHz

Microwaves and neighboring networks crowd the limited 2.4 GHz channels.

Network Devices

Different hardware operates at different layers to move data. Knowing what each device does helps isolate where a problem occurs.

Switches forward by MAC address

A Layer 2 switch learns MACs and forwards frames only to the correct port.

Routers connect networks

A router forwards packets between networks at Layer 3 using IP addresses.

NAT shares one public IP

Network Address Translation lets many private hosts use a single public address.

Hubs are obsolete

Hubs repeat traffic to all ports, causing collisions; switches replaced them.

Cabling and Connectors

Physical media carries the signal. Choosing the right cable category and connector ensures the link meets the required speed and distance.

RJ45 terminates twisted pair

Ethernet uses 8-pin RJ45 connectors; RJ11 is for telephone lines.

Cat 6a supports 10 Gbps

It carries 10 Gigabit Ethernet up to 100 meters, unlike Cat 5.

Fiber for long distance and EMI immunity

Optical cable resists interference and spans longer runs than copper.

Test suspect cables

A cable tester verifies correct end-to-end termination and continuity.

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