Capítulo 3 de 520% del examen

Networking Fundamentals: TCP/IP, DNS, and DHCP

Networking connects computers so they can share data and services, and it is central to modern IT support. This chapter explains how devices are addressed, how data moves reliably across networks, and the key services like DNS and DHCP that make networks usable. A firm grasp of these concepts is essential for diagnosing connectivity problems.

Addressing and the TCP/IP Model

The internet relies on the Internet Protocol to address and route data between devices. Addresses identify hosts, and the TCP/IP suite defines how data is packaged and delivered. Understanding addressing is the first step to understanding networks.

IP addresses identify devices

The Internet Protocol assigns each device an address used to route packets; IPv4 uses 32-bit addresses and IPv6 uses 128-bit addresses.

Subnet masks split network and host

A mask such as 255.255.255.0 defines which part of an IP address is the network and which is the host, guiding routing decisions.

MAC addresses are hardware IDs

Each network interface has a unique MAC address used for communication within a local network segment at the data link layer.

The default gateway reaches outside

Traffic destined for other networks is sent to the default gateway, usually a router, which forwards it toward its destination.

Transport Protocols: TCP and UDP

Once devices are addressed, transport protocols govern how data is delivered. TCP and UDP offer different trade-offs between reliability and speed. Choosing between them depends on the application's needs.

TCP is reliable and ordered

Transmission Control Protocol establishes a connection and guarantees data arrives correctly and in order, retransmitting lost packets.

UDP is fast and connectionless

User Datagram Protocol sends data without guaranteeing delivery, trading reliability for lower overhead, ideal for streaming and gaming.

Ports identify services

Port numbers direct traffic to the right application, such as port 80 for HTTP, 443 for HTTPS, and 53 for DNS.

The OSI model has seven layers

This conceptual framework, from physical to application, helps organize and troubleshoot how network communication works.

Core Network Services: DNS and DHCP

Two services make networks convenient to use: DNS translates names to addresses, and DHCP assigns addresses automatically. Without them, using and administering networks would be far more difficult. Both are frequent sources of troubleshooting questions.

DNS resolves names to IPs

The Domain Name System acts like a phone book, translating domain names such as example.com into the IP addresses computers use.

DHCP assigns addresses automatically

The Dynamic Host Configuration Protocol hands out IP addresses, subnet masks, gateways, and DNS servers to devices as they join.

Leases are temporary

DHCP assigns addresses for a limited lease period, after which they are renewed or returned to the pool for reuse.

DNS problems mimic outages

If DNS fails, sites appear unreachable by name even though the connection works, a common troubleshooting scenario.

Network Devices and Traffic Flow

Physical and logical devices move data within and between networks. Switches connect local devices, routers connect networks, and NAT lets many devices share one public address. Knowing each device's role clarifies how traffic flows.

Switches connect local devices

A switch forwards frames within a local network to the correct port based on MAC addresses, more efficiently than an older hub.

Routers connect networks

A router forwards packets between different networks, such as a home network and the internet, choosing paths via routing tables.

NAT shares a public IP

Network Address Translation lets many private devices share a single public IP address, conserving scarce IPv4 addresses.

Firewalls filter traffic

A firewall permits or blocks network traffic according to security rules, forming a barrier between trusted and untrusted networks.

Network Troubleshooting Tools

Several command-line tools help diagnose network problems by testing connectivity and revealing configuration. Learning them lets you quickly locate where a network issue occurs. They are staples of everyday IT support.

ping tests reachability

The ping command sends echo requests to a host and reports whether replies return and how long they take, confirming basic connectivity.

traceroute maps the path

Traceroute, or tracert on Windows, lists each router hop between source and destination to locate where delays or failures occur.

ipconfig shows configuration

On Windows, ipconfig displays IP address, subnet mask, and gateway; ipconfig /all adds DNS servers and the MAC address.

HTTPS secures web traffic

HTTPS uses TLS to encrypt data between browser and server, protecting information and indicated by a padlock in the browser.

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Last updated: July 2026