Networking

TFTP and FTP

Trivial File Transfer Protocol and File Transfer Protocol for network file transfers with varying security and reliability

TFTP (Trivial File Transfer Protocol)

  • Lightweight file transfer protocol designed for simplicity over features
  • Uses UDP port 69 (connectionless, no reliability guarantees)
  • No authentication - relies on network-level security
  • No directory listing - must know exact filename
  • Maximum file size limited to 32MB due to 16-bit block numbering
  • Primarily used for network device operations (router/switch firmware, config backups)

FTP (File Transfer Protocol)

  • Full-featured file transfer protocol with comprehensive functionality
  • Uses TCP ports 20 (data) and 21 (control) for reliable delivery
  • Requires authentication with username/password
  • Supports directory browsing, file management, and multiple transfer modes
  • No practical file size limitations
  • Two connection modes: Active (server initiates data connection) and Passive (client initiates both connections)

Protocol Comparison

Feature TFTP FTP
Transport Protocol UDP (port 69) TCP (ports 20/21)
Authentication None Username/Password
Security Minimal Basic (cleartext by default)
File Size Limit 32MB No practical limit
Directory Operations No Yes
Reliability None (UDP) Built-in (TCP)
Complexity Minimal Full-featured
Typical Use Device management General file transfer

Common Use Cases

TFTP Applications:

  • Router/switch firmware upgrades (copy tftp: flash:)
  • Configuration file backups (copy running-config tftp:)
  • PXE boot environments for network installations
  • Cisco IP phone firmware delivery
  • Small file transfers in controlled environments

FTP Applications:

  • Large file transfers between systems
  • Website content management
  • Database backups and synchronization
  • Software distribution
  • General-purpose file sharing (though largely replaced by SFTP/FTPS)

Vocabulary

Active FTP: Server initiates data connection back to client (can cause firewall issues)

Passive FTP: Client initiates both control and data connections (firewall-friendly)

Block Size: TFTP transfers files in 512-byte blocks by default (can negotiate larger)

Acknowledgment: TFTP requires ACK for each block before sending next (stop-and-wait)

Binary vs ASCII: Transfer modes - binary for executables/images, ASCII for text files

Notes

  • TFTP is inherently insecure - use only on trusted networks or with VPN protection
  • TFTP’s simplicity makes it ideal for embedded systems with limited memory/processing
  • For production environments, consider SFTP (SSH File Transfer Protocol) or FTPS (FTP over SSL/TLS) instead of standard FTP
  • TFTP timeout and retry mechanisms vary by implementation - typically 5-second timeouts with 5 retries
  • When using copy commands on Cisco devices, TFTP is often the default protocol unless otherwise specified
  • FTP active mode often blocked by firewalls since server connects back to client - use passive mode for NAT/firewall traversal
  • Both protocols transfer credentials and data in cleartext - monitor network access carefully