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RFC 1350 / TFTP · ONE BLOCK AT A TIME

Reject stray traffic and respect the limits

05

Most errors stop a transfer. A packet from an unexpected transfer port is the exception: reject that packet without killing the valid transfer.

DIAGRAMRead RFC section 7 ↗
RFC 1350 · § 7EXAMPLE
5 / 5
Reject stray traffic and respect the limitsFive separate cases show an unexpected server50001 being discarded and sent ERROR5 without stopping the valid40000/50000 transfer; missing-file ERROR1 terminating a separate request; lost ERROR requiring peer timeout; a chosen read-only server policy denying a write with ERROR2; and a clear boundary between base512-byte blocks and later client-requested negotiated extensions. TID matching is not authentication and no encryption/login is invented.Separate failure and scope examplesBASE: no options requested512 data bytes per full blockLATER: negotiated options2347 · 2348 · 2349Only requested and accepted options applyNot a new base TFTP packet sequence here
05
Keep later options separate.

Base transfer: no options and 512-byte data blocks. Negotiated extensions in RFCs 2347–2349 change specific rules only when accepted.

Source for this drawing: RFC 1350 · Read RFC section 7 ↗

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Related RFCs and changes

“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.

What changed
RFC 1350 base protocolRFC 2347 Negotiation Protocol

RFC 2347 adds client-requested option negotiation; RFCs 2348 and 2349 define block size and timeout/transfer-size options. This guide’s base examples request none of them.

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KEY POINT

A transfer ID is a routing check, not authentication.

  • If a source TID does not match the established transfer, the packet should be discarded and ERROR code 5 returned to its source, without disturbing the valid transfer (§4).
  • ERROR normally ends the transfer. It is neither acknowledged nor retransmitted; timeouts must also detect failure if the error itself is lost. Codes include 1 file not found, 2 access violation and 3 disk full/allocation exceeded.
  • TFTP has no user authentication or built-in access-control mechanism. Server-process permissions and configured path policy must limit access; RFC 1123 §4.2.3.4 says configurable pathname access control SHOULD be included.
DETAILS

The last scene is a scope boundary, not an extra base opcode exchange. Official metadata lists updates 1782/1783/1784/1785/2347/2348/2349; 2347/2348/2349 obsolete 1782/1783/1784 respectively. Option negotiation, block size and timeout/size extensions are separate. RFC 2347 allows only client-requested options in OACK; unacknowledged options are ignored. The base drawings use no options and remain at 512. Port checks and restricted files do not provide encryption, peer authentication or a safe untrusted-network file service.

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