The last two bits are used for ECN I believe.

-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of bill fumerola
Sent: Tuesday, November 28, 2006 3:13 PM
To: Awais Awan
Cc: [email protected]
Subject: Re: [Flow-tools] flow tools tcp flags

On Tue, Nov 28, 2006 at 08:03:51PM +0000, Awais Awan wrote:
> We know that there are 6 possible flags for TCP which are
> URG-ACK-PSH-RST-SYN-FIN (ox2 giving us SYN)
> 
> But net-flow reserves 8 bits for ip-tcp-flags (0-255 values) Can anyone 
> tell me why net-flow has kept 8 bits for ip-tcp-flags? and what are the 
> other two bits?

because that's how big the field on the wire is.

Vladis already answered what the other two bits are:
http://mailman.splintered.net/pipermail/flow-tools/2006-November/003354.html

from /usr/include/netinet/tcp.h on osx/freebsd:

#define TH_ECE  0x40
#define TH_CWR  0x80

-- bill


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