Snort mailing list archives
Re: TCP reserved flags: which is it?
From: John Sage <jsage () finchhaven com>
Date: Sun, 21 Jul 2002 22:59:42 -0700
arf.. 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 as flags=21****S* 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 noticed :-) - John -- "Obviously, we do not want to leave zombies around." PGP key http://www.finchhaven.com/pages/gpg_pubkey.html Fingerprint FE 97 0C 57 08 43 F3 EB 49 A1 0C D0 8E 0C D0 BE C8 38 CC B5 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].
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Current thread:
- TCP reserved flags: which is it? John Sage (Jul 17)
- Win32 - libpcap questrion Anonymous - Mike (Jul 18)
- Re: Win32 - libpcap questrion Erek Adams (Jul 18)
- Re: TCP reserved flags: which is it? John Sage (Jul 20)
- Re: TCP reserved flags: which is it? Phil Wood (Jul 21)
- Re: TCP reserved flags: which is it? John Sage (Jul 21)
- Re: TCP reserved flags: which is it? Phil Wood (Jul 22)
- Re: TCP reserved flags: which is it? John Sage (Jul 22)
- Re: TCP reserved flags: which is it? Phil Wood (Jul 21)
- Win32 - libpcap questrion Anonymous - Mike (Jul 18)
- Re: TCP reserved flags: which is it? John Sage (Jul 21)
- Re: TCP reserved flags: which is it? John Sage (Jul 22)