CCNA 200-301 v1.1 reference — Network Fundamentals
TCP and UDP
How TCP provides reliable, ordered delivery and how UDP trades that for low overhead, with port numbers and protocol numbers used across the CCNA.
Objective 1.5v1.1 exam target
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TCP versus UDP
| Property | TCP | UDP |
|---|---|---|
| Delivery | Reliable, acknowledged, retransmitted | Best effort, no retransmission |
| Ordering | Sequenced byte stream | No ordering guarantees |
| Connection | Connection-oriented (3-way handshake) | Connectionless |
| Overhead | 20-byte header minimum | 8-byte header |
| Flow control | Sliding window | None |
| Use when | Loss is unacceptable (web, email, file transfer) | Speed/simplicity matters; loss is tolerable or handled above (DNS, DHCP, VoIP, streaming) |
Common IP protocol numbers
| Protocol number | Protocol | Notes |
|---|---|---|
| 1 | ICMP | Ping, errors, path discovery |
| 2 | IGMP | Multicast group membership |
| 6 | TCP | Reliable stream transport |
| 17 | UDP | Lightweight datagram transport |
| 50 | ESP | IPsec encapsulated security payload |
| 51 | AH | IPsec authentication header |
| 88 | EIGRP | Cisco interior routing protocol |
| 89 | OSPF | Link-state routing protocol |
Protocol numbers live in the IP header and name the upper-layer protocol — they are not TCP/UDP ports.
Well-known TCP ports
| Port | Service | Purpose |
|---|---|---|
| 20 | FTP data | Active-mode data channel |
| 21 | FTP control | Commands and replies |
| 22 | SSH | Secure remote access and SFTP |
| 23 | Telnet | Insecure remote access |
| 25 | SMTP | Mail transfer |
| 53 | DNS | Zone transfers and large responses |
| 80 | HTTP | Unencrypted web |
| 110 | POP3 | Mail retrieval |
| 143 | IMAP | Mail access |
| 443 | HTTPS | Encrypted web |
| 179 | BGP | Inter-AS routing (context) |
Well-known UDP ports
| Port | Service | Purpose |
|---|---|---|
| 53 | DNS | Standard name queries |
| 67/68 | DHCP | Server / client |
| 69 | TFTP | Trivial file transfer |
| 123 | NTP | Time synchronization |
| 161 | SNMP | Agent polling |
| 162 | SNMP traps | Manager receives notifications |
| 514 | Syslog | Log forwarding |
| 520 | RIP | Routing updates (context) |
| 1812/1813 | RADIUS | Authentication / accounting |
| 500 | IKE | IPsec key exchange |
Related resources
Sources
- Cisco CCNA 200-301 v1.1 Exam Topics (official PDF) — reviewed 2026-11-02
- RFC 9293 — Transmission Control Protocol (TCP) — reviewed 2026-11-02
- RFC 768 — User Datagram Protocol — reviewed 2026-11-02
Targets CCNA 200-301 v1.1 objectives. Supplemental blocks are labeled beyond exam scope.