Common Network Protocols: What Each Does, Its Port, and How They Work Together

Network protocols are standardized rules that define how data is transmitted and received across devices in a computer network. This blog explains key protocols like HTTP, TCP/IP, FTP, DNS, and more, with a detailed table covering their functions, ports, and usage. These protocols are essential for establishing reliable communication between systems, ensuring secure data transfer, and supporting internet and local network operations.

Jul 19, 2025 - 12:42

Updated: 1 month ago

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Common Network Protocols: What Each Does, Its Port, and How They Work Together

Quick answer: Common network protocols include IP, TCP, UDP, ICMP, ARP, DHCP, DNS, HTTP and HTTPS, SSH, FTP, SMTP, IMAP, SNMP and BGP. Each does one job at one layer: IP routes packets, TCP delivers reliably, UDP delivers fast, DNS resolves names, and HTTPS carries encrypted web traffic on port 443.

Key takeaways

Protocols are rules for communication, layered so each does one job.
TCP is reliable and connection-based; UDP is fast and connectionless.
Opening a website uses DHCP, DNS, ARP, TCP, TLS, HTTP and IP together.
Prefer secure versions: HTTPS, SSH, SFTP and SNMPv3.

What is a network protocol?

A network protocol is an agreed set of rules for how devices format, send, receive and check data. Without shared rules, a laptop in Pune could not talk to a server in Mumbai. Protocols are layered, so each one does one job and relies on the one below it.

What are the most common protocols, by job?

Protocol	Job	Transport and default port	Notes
IP (IPv4, IPv6)	Addressing and routing packets	Network layer, no port	Every host needs an IP address
TCP	Reliable, ordered delivery	Transport layer	Three-way handshake, retransmission
UDP	Fast delivery without guarantees	Transport layer	Used by DNS queries, streaming, VoIP
ICMP	Error messages and diagnostics	Network layer, no port	ping and traceroute use it
ARP	Maps an IPv4 address to a MAC address	Link layer	Local network only
DHCP	Gives devices IP settings automatically	UDP 67 (server), 68 (client)	Lease based
DNS	Translates names to IP addresses	UDP and TCP 53	Hierarchical, cached
HTTP	Web requests and responses	TCP 80	Plain text
HTTPS (HTTP over TLS)	Encrypted web traffic	TCP 443	Uses TLS certificates
SSH	Encrypted remote login and file copy (SFTP, SCP)	TCP 22	Replaces Telnet
Telnet	Unencrypted remote login	TCP 23	Avoid; credentials are visible
FTP	File transfer	TCP 21 control, 20 data (active)	Unencrypted; prefer SFTP or FTPS
SMTP	Sending email between servers	TCP 25; 587 or 465 for client submission	Used with TLS in modern setups
POP3 and IMAP	Retrieving email	110 and 143; 995 and 993 with TLS	IMAP keeps mail on the server
SNMP	Monitoring network devices	UDP 161, 162	Use SNMPv3 for security
NTP	Clock synchronisation	UDP 123	Needed for logs and certificates
LDAP	Directory lookups	TCP 389; 636 with TLS	Active Directory uses it
SMB	Windows file and printer sharing	TCP 445	Do not expose to the internet
RDP	Remote Windows desktop	TCP 3389	A common attack target
BGP	Exchanging routes between networks	TCP 179	Runs the internet's routing
OSPF	Routing inside an organisation	IP protocol 89, no port	Link-state

Port numbers are defaults. Services can run on other ports, so do not treat a port as proof of what is running.

TCP and UDP in plain words

TCP sets up a connection first (SYN, SYN-ACK, ACK), numbers the data, acknowledges it and resends what is lost. Use it when every byte matters, as in web pages, email and file copies. UDP just sends. There is no setup and no resend, which makes it quick and light. Use it when speed matters more than perfection, as in a voice call, where a lost fragment is better skipped than delayed. The current TCP specification is RFC 9293.

What happens when you open a website?

DHCP already gave your device an IP address, mask, gateway and DNS server.
DNS turns the name (for example www.example.com) into an IP address.
ARP finds the gateway's MAC address on your local network.
TCP opens a connection to the server's port 443.
TLS agrees on encryption and checks the server's certificate.
HTTP carries your request and the page comes back.
IP and the routers (using protocols such as OSPF inside a company and BGP between networks) move every packet along the way.

You can watch parts of this yourself:

dig www.example.com # DNS lookup
ip neigh # ARP table on Linux (arp -a on Windows)
traceroute www.example.com # ICMP/UDP path (tracert on Windows)
curl -v https://www.example.com/ # TCP, TLS and HTTP in one request

Run curl -v and read the lines for the connection, the TLS handshake and the HTTP headers. For specifications, see the HTTP semantics RFC 9110 and TLS 1.3, RFC 8446.

Secure and insecure versions

Insecure	Prefer
HTTP	HTTPS
Telnet	SSH
FTP	SFTP or FTPS
SNMP v1 and v2c	SNMPv3
POP3, IMAP and SMTP without TLS	The same with TLS

Why this matters for your career

Protocols are the vocabulary of networking and security. CCNA tests them directly, and tools such as Wireshark and Nmap are much easier to use once you know what a normal DNS query, a TCP handshake or a DHCP exchange looks like. The first step to spotting an attack is knowing what normal traffic looks like.

Next steps

Learn protocols with hands-on labs in the CCNA 200-301 course. Related reading: the TCP/IP model and protocols across OSI layers.

Frequently Asked Questions

Network protocols are agreed rules for how devices format, send, receive and check data across a network. Without them, devices from different makers could not communicate. Protocols are layered, and each handles one job.

TCP sets up a connection, numbers and acknowledges data and resends lost parts, so it is reliable. UDP sends without setup or acknowledgement, so it is faster but offers no guarantee. Web pages use TCP, voice calls often use UDP.

HTTPS uses TCP port 443 by default. It is HTTP carried over TLS, which encrypts traffic and checks the server's certificate. HTTP without encryption uses port 80.

DNS translates human-readable names such as www.example.com into IP addresses. It mainly uses UDP port 53 and falls back to TCP 53 for larger responses. Results are cached to speed up later lookups.

DHCP gives your device its address, DNS resolves the name, ARP finds the local gateway, TCP opens a connection, TLS encrypts it, HTTP carries the request, and IP and routing protocols move the packets.

Telnet, plain FTP, HTTP, SNMP v1 and v2c, and mail protocols without TLS send data unencrypted. Replace them with SSH, SFTP or FTPS, HTTPS, SNMPv3 and TLS-protected mail.

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Vaishnavi

Vaishnavi is a skilled tech professional at the Ethical Hacking Training Institute in Pune, responsible for managing and optimizing the technical infrastructure that supports advanced cybersecurity education. With deep expertise in network security, backend operations, and system performance, she ensures that practical labs, online modules, and assessments run smoothly and securely. Her behind-the-scenes contributions play a vital role in delivering a seamless and secure learning experience for aspiring ethical hackers.