From owner-freebsd-bugs Mon Oct 28 19:10: 4 2002 Delivered-To: freebsd-bugs@hub.freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id B0CAB37B401 for ; Mon, 28 Oct 2002 19:10:03 -0800 (PST) Received: from freefall.freebsd.org (freefall.freebsd.org [216.136.204.21]) by mx1.FreeBSD.org (Postfix) with ESMTP id 7334143E6E for ; Mon, 28 Oct 2002 19:10:03 -0800 (PST) (envelope-from gnats@FreeBSD.org) Received: from freefall.freebsd.org (gnats@localhost [127.0.0.1]) by freefall.freebsd.org (8.12.6/8.12.6) with ESMTP id g9T3A3x3003626 for ; Mon, 28 Oct 2002 19:10:03 -0800 (PST) (envelope-from gnats@freefall.freebsd.org) Received: (from gnats@localhost) by freefall.freebsd.org (8.12.6/8.12.6/Submit) id g9T3A30F003625; Mon, 28 Oct 2002 19:10:03 -0800 (PST) Date: Mon, 28 Oct 2002 19:10:03 -0800 (PST) Message-Id: <200210290310.g9T3A30F003625@freefall.freebsd.org> To: freebsd-bugs@FreeBSD.org Cc: From: kenji@k2r.org Subject: Re: misc/39787: T/TCP support Reply-To: kenji@k2r.org Sender: owner-freebsd-bugs@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org The following reply was made to PR misc/39787; it has been noted by GNATS. From: kenji@k2r.org To: freebsd-gnats-submit@FreeBSD.org, dhuang@qobra.com Cc: kenji@k2r.org Subject: Re: misc/39787: T/TCP support Date: 29 Oct 2002 12:00:17 +0900 The reason of this behavior is documented in /usr/src/sys/netinet/tcp_syncache.c (I quote from the 4.6.2-RELEASE version, src/sys/netinet/tcp_syncache.c,v 1.5.2.6) as follows, just before the function syncache_add(): - quote - * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. * Doing so would require that we hold onto the data and deliver it * to the application. However, if we are the target of a SYN-flood * DoS attack, an attacker could send data which would eventually * consume all available buffer space if it were ACKed. By not ACKing * the data, we avoid this DoS scenario. - unquote - So I'd rather consider this as an *intentional feature* of FreeBSD to block SYN-flooding. // Kenji Rikitake To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message