[SATLUG] OT: question about TCP headers
toddwbucy at grandecom.net
Wed Jan 27 08:15:41 CST 2010
On Tue, 2010-01-26 at 22:27 -0600, Jon Mark Allen wrote:
> On Tue, Jan 26, 2010 at 22:12, redpill <toddwbucy at grandecom.net> wrote:
> > background:
> > I am currently taking Kolars TCP/IP class at SAC and this question
> > relates to a non-graded lab.
> > references:
> > class text - TCP/IP Illustrated Volume 1: the protocols cira 1994
> > web reference png image illustrating the TCP header breakdown -
> > http://freebie.fatpipe.org/~mjb/Drawings/TCP-Header.png
> > question:
> > the text notes that there are 6 reserved bits between the header length
> > and the flags (page 225). The image noted above has shown 4 bits
> > reserved between the length and the flags. 2 additional flags are added
> > on the png file that are not listed in the book: C 0x80 Reduced (CWR)
> > and E 0x40 ECN Echo (ECE). Which one is correct? I was shown this file
> > by a classmate and I need to confirm its accuracy.
> > Challenge:
> > you will win my vote for uber geek of the year if you can give me the
> > RFC's that may clarify this issue.
> > Thanks
> > Todd
> RFC 793 is the original RFC for TCP. Viewing  shows at the top
> that RFC has been "updated" by RFCs 1122  and 3168 . The
> abstract of RFC3168 states:
> "This memo specifies the incorporation of ECN (Explicit Congestion
> Notification) to TCP and IP, including ECN's use of two bits in the IP
> Given that 3168 was issue in September of 2001, that would explain why
> it isn't mentioned in the book.
>  http://tools.ietf.org/html/rfc793
>  http://tools.ietf.org/html/rfc1122
>  http://tools.ietf.org/html/rfc3168
> /* If you haven't found something strange during the day, it hasn't
> been much of a day.
> -- John A. Wheeler */
thanks for the info. I was originally referring to to the faqs.org's
copy of the RFC 793, http://www.faqs.org/rfcs/rfc793.html, which doesn't
refer to the other updates. So not only did you give me the info that I
needed but you pointed me to a better source for my RFC's. You win my
vote for Uber Geek of the year:) The year is still very young so keep
showing off that brain of yours.
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