From owner-freebsd-questions Thu Mar 20 16:43:22 2003 Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id BFCDC37B401 for ; Thu, 20 Mar 2003 16:43:20 -0800 (PST) Received: from mailsrv.otenet.gr (mailsrv.otenet.gr [195.170.0.5]) by mx1.FreeBSD.org (Postfix) with ESMTP id 7CAC843FA3 for ; Thu, 20 Mar 2003 16:43:19 -0800 (PST) (envelope-from keramida@ceid.upatras.gr) Received: from gothmog.gr (patr530-a182.otenet.gr [212.205.215.182]) by mailsrv.otenet.gr (8.12.8/8.12.8) with ESMTP id h2L0hD5u023524; Fri, 21 Mar 2003 02:43:13 +0200 (EET) Received: from gothmog.gr (gothmog [127.0.0.1]) by gothmog.gr (8.12.8/8.12.8) with ESMTP id h2L0hCkg002070; Fri, 21 Mar 2003 02:43:12 +0200 (EET) (envelope-from keramida@ceid.upatras.gr) Received: (from giorgos@localhost) by gothmog.gr (8.12.8/8.12.8/Submit) id h2L0hCHQ002069; Fri, 21 Mar 2003 02:43:12 +0200 (EET) (envelope-from keramida@ceid.upatras.gr) Date: Fri, 21 Mar 2003 02:43:12 +0200 From: Giorgos Keramidas To: John Fitzgibbon Cc: freebsd-questions@FreeBSD.org Subject: Re: Repeated ACKs - possible DoS? Message-ID: <20030321004312.GA1964@gothmog.gr> References: <200303201408.53238.fitz@jfitz.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200303201408.53238.fitz@jfitz.com> X-RAVMilter-Version: 8.4.2(snapshot 20021217) (terpsi) Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On 2003-03-20 14:08, John Fitzgibbon wrote: > Notes: > X is the remote machine. > Y is my server, (FreeBSD 4.7-STABLE, built 2003/01/06) > > tcpdump showing 2 remote connections repeatedly sending "ack 1": > > 09:16:10.236812 X.64670 > Y.http: . ack 1 win 32589 > 09:16:10.236879 Y.http > X.64670: . ack 489 win 58400 (DF) > 09:16:10.242978 X.64670 > Y.http: . ack 1 win 32589 > 09:16:10.243037 Y.http > X.64670: . ack 489 win 58400 (DF) > 09:16:10.248883 X.64677 > Y.http: . ack 1 win 32767 > 09:16:10.248946 Y.http > X.64677: . ack 25 win 58400 (DF) > 09:16:10.255044 X.64670 > Y.http: . ack 1 win 32589 > 09:16:10.255123 Y.http > X.64670: . ack 489 win 58400 (DF) > 09:16:10.262925 X.64677 > Y.http: . ack 1 win 32767 > 09:16:10.262989 Y.http > X.64677: . ack 25 win 58400 (DF) > 09:16:10.268842 X.64670 > Y.http: . ack 1 win 32589 > 09:16:10.268905 Y.http > X.64670: . ack 489 win 58400 (DF) > 09:16:10.275241 X.64670 > Y.http: . ack 1 win 32589 > 09:16:10.275303 Y.http > X.64670: . ack 489 win 58400 (DF) Hmmm, is this repeatable? Can you try to grab the output of the following command in a log file while it happens? # tcpdump -n -v -s 128 -XX port 80 - Giorgos To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message