RFC 5925, "The TCP Authentication Option", June 2010

Errata ID: 4365
Status: Verified
Type: Technical
Publication Format(s) : TEXT
Reported By: Joe Touch
Date Reported: 2015-05-12
Verifier Name: Martin Stiemerling
Date Verified: 2015-12-16

Section 7.6 says:

   TCP's 4-bit data offset requires that the options end 60 bytes (15
   32-bit words) after the header begins, including the 20-byte header.
   This leaves 40 bytes for options, of which 15 are expected in current
   implementations (listed below), leaving at most 25 for other uses.
   TCP-AO consumes 16 bytes, leaving 9 bytes for additional SYN options
   (depending on implementation dependant alignment padding, which could
   consume another 2 bytes at most).

   o  SACK permitted (2 bytes) [RFC2018][RFC3517]

   o  Timestamps (10 bytes) [RFC1323]

   o  Window scale (3 bytes) [RFC1323]

It should say:

   TCP's 4-bit data offset requires that the options end 60 bytes (15
   32-bit words) after the header begins, including the 20-byte header.
   This leaves 40 bytes for options, of which 19 are expected in current
   implementations (listed below), leaving at most 21 for other uses.
   TCP-AO consumes 16 bytes, leaving 5 bytes for additional SYN options
   (depending on implementation dependent alignment padding, which could
   consume another 2 bytes at most).

   o  SACK permitted (2 bytes) [RFC2018][RFC3517]

   o  Timestamps (10 bytes) [RFC1323]

   o  Window scale (3 bytes) [RFC1323]

   o  Maximum Segment Size (4 bytes) [RFC793]

Notes:

MSS was missing in the original text. New text includes MSS and updates numbers accordingly.

Also corrects a spelling error (dependant -> dependent), which is non-technical but included in the revised text.

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