5.9. TFTP and FTP
💡 First Principle: File transfer protocols move files between devices—critical for IOS upgrades, configuration backups, and disaster recovery. TFTP is simple but insecure (no authentication); FTP adds authentication but complexity. The wrong choice in the wrong situation can brick devices or expose sensitive configurations.
What happens when file transfers go wrong: Imagine you're upgrading a router's IOS. Halfway through the transfer, the network blips and TFTP fails. Now the router has a corrupted image—it won't boot from the incomplete file. Without a backup image or ROMMON access, you have an expensive paperweight. This is why you verify file hashes after transfer and always have a recovery plan.
Consider this security scenario: Your TFTP server is on the user VLAN because "it's more convenient." An attacker on that VLAN downloads your router configs, extracts password hashes (even type 7 encrypted passwords are trivially reversible), and now has credentials for your entire network. TFTP has zero authentication—if you can reach it, you can read from it.
Why this matters:
- Config backup before changes:
copy running-config tftp://server/backup.cfgcould save your job - IOS upgrades: Corrupted or interrupted transfers can make devices unbootable
- Disaster recovery: Working backups mean 10-minute recovery vs rebuilding from scratch
TFTP (Trivial File Transfer Protocol):
- UDP port 69
- No authentication
- Simple read/write operations
- Used for firmware updates, config backups
FTP (File Transfer Protocol):
- TCP ports 20 (data) and 21 (control)
- Authentication required
- Full file management (directories, delete, rename)
- More secure than TFTP because it authenticates, but credentials and data still cross the network in cleartext
SFTP and SCP run over SSH (TCP 22) and encrypt both the login and the file.
Common Use:
Router# copy running-config tftp://10.1.1.100/router-config.txt
Router# copy tftp://10.1.1.100/ios-image.bin flash:
