From owner-freebsd-ipfw Fri Dec 21 21:32:24 2001 Delivered-To: freebsd-ipfw@freebsd.org Received: from gate.killian.com (gate.killian.com [205.179.65.162]) by hub.freebsd.org (Postfix) with ESMTP id 0C2BC37B416 for ; Fri, 21 Dec 2001 21:32:13 -0800 (PST) Received: (from root@localhost) by gate.killian.com (8.11.6/8.11.6) id fBM5Vui36708; Fri, 21 Dec 2001 21:31:56 -0800 (PST) (envelope-from earl) Date: Fri, 21 Dec 2001 21:31:56 -0800 (PST) Message-Id: <200112220531.fBM5Vui36708@gate.killian.com> From: "Earl A. Killian" To: freebsd-ipfw@freebsd.org Subject: keep-state Sender: owner-freebsd-ipfw@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG I tried a firewall using keep-state and ran into a problem. I am looking for suggestions on the best way to fix it. My firewall was essentially <> divert natd all from any to any via ${oif} check-state <> The problem is that the firewall is invoked twice, on both input and output. A host on the inside initiates a connection by sending a SYN packet from INSIDE-IP to OUTSIDE-IP. This was accepted via one of the filters and a keep-state was done. Next, the kernel determines that the packet is destined for outside, so it is run through the rules a second time on the way out. This time it is diverted to natd which rewrites it to a packet from OIF-IP to OUTSIDE-IP. Another dynamic rule is created for this by a susequent keep-state. When the SYN ACK comes back from OUTSIDE-IP to GATE, it is diverted on input to natd, which rewrites it as OUTSIDE-IP to INSIDE-IP. This hits the check-state and is accepted by the first dynamic rule created above, and ups the lifetime of the rule to 1000s. However, the second dynamic rule created above will eventually time out (it has only a 20s lifetime because it never sees the SYN ACK), at which point the connection is blocked (further packets from INSIDE-IP to OUTSIDE-IP will be dropped on the floor on output). One way to fix this would be to augment the rules to accept anything output from the gateway to the internet: <> divert natd all from any to any via ${oif} allow all from ${oip} to any out xmit ${oif} check-state <> This will prevent the need for the second dynamic rule. However, it seems to compromise security somewhat since it is fairly permissive, and generally one follows the rule that anything not required is denied. Is there a better way? -Earl To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-ipfw" in the body of the message