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RFC 791, "Internet Protocol", September 1981

Note: This RFC has been updated by RFC 1349, RFC 2474, RFC 6864

Source of RFC: Legacy
Area Assignment: int
See Also: RFC 791 w/ inline errata

Errata ID: 6356
Status: Verified
Type: Technical
Publication Format(s) : TEXT

Reported By: Patrick Ni
Date Reported: 2020-12-15
Verifier Name: Eric Vyncke
Date Verified: 2021-01-04

Section 3.2 says:

(14) THEN TL <- TDL+(IHL*4)

It should say:

(14) THEN TL <- TDL+(IHL-Of-First-Fragment*4)


IHL could be different between the first fragment and the rest. Only the first fragment's IHL is the same as the one in the original datagram before fragmentation

--- Verifier note ---
Updated the type of errata to technical from editorial.

Section 3.2 of RFC 791 clearly states that "When fragmentation occurs, some options are copied, but others remain with the first fragment only." so IHL varies from fragment to fragment. Therefore when copying the IP header of the F=0 fragment (step 11) all options are rightfully copied and must be counted in the re-assembled fragment total length on step 14 as noted by Patrick Ni.

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