Date: Fri, 21 Mar 2003 02:43:12 +0200 From: Giorgos Keramidas <keramida@ceid.upatras.gr> To: John Fitzgibbon <fitz@jfitz.com> Cc: freebsd-questions@FreeBSD.org Subject: Re: Repeated ACKs - possible DoS? Message-ID: <20030321004312.GA1964@gothmog.gr> In-Reply-To: <200303201408.53238.fitz@jfitz.com> References: <200303201408.53238.fitz@jfitz.com>
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On 2003-03-20 14:08, John Fitzgibbon <fitz@jfitz.com> 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
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