[Snort-users] TCP reserved flags: which is it?
jsage at ...2022...
Sun Jul 21 23:00:05 EDT 2002
Actually, if you had read my initial post, the *real* question was
why snort reported the flags as 12****S* while ACID reports the flags
Notice the "1" and the "2" are reversed between the two.
I know *what* the flags mean; I'm just trying to understand why snort
and ACID seem to be reporting them differently...
(That, and I was kinda funnin' with Erek, but he doesn't seem to have
"Obviously, we do not want to leave zombies around."
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On Sun, Jul 21, 2002 at 12:14:27PM -0600, Phil Wood wrote:
> On Sat, Jul 20, 2002 at 10:10:00PM -0700, John Sage wrote:
> > On Wed, Jul 17, 2002 at 11:38:31PM -0700, John Sage wrote:
> > > Received some tcp:25 packets with the reserved flag bits set.
> > <snip>
> > What about my question?
> > Guys?
> Take a look at rfc2481 and rfc2914.txt. Those bits are being used
> for explicit congestion control. Of course it only works if both ends
> and intervening routers are participating. Here is a snippit from rfc 2481:
> 6.1. TCP
> The following sections describe in detail the proposed use of ECN in
> TCP. This proposal is described in essentially the same form in
> [Floyd94]. We assume that the source TCP uses the standard congestion
> control algorithms of Slow-start, Fast Retransmit and Fast Recovery
> [RFC 2001].
> This proposal specifies two new flags in the Reserved field of the
> TCP header. The TCP mechanism for negotiating ECN-Capability uses
> the ECN-Echo flag in the TCP header. (This was called the ECN Notify
> flag in some earlier documents.) Bit 9 in the Reserved field of the
> TCP header is designated as the ECN-Echo flag. The location of the
> 6-bit Reserved field in the TCP header is shown in Figure 3 of RFC
> 793 [RFC793].
8< snip >8
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