From mboxrd@z Thu Jan 1 00:00:00 1970 From: paddy joesoap Subject: Forward Chain: is Inbound traffic on eth0 not also Outbound depending on your view? Date: Sun, 8 Nov 2009 11:11:44 +0000 Message-ID: Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:date:message-id:subject :from:to:content-type; bh=hiZ69zc3u4SHHlRpbMkhtRZnTBdsF2fgHRoyBdND0Zs=; b=d0I07edRfVjoN0c4659+0nUV7lUVgVXaAToy8iYsUJdpRqafMOVLSbCXQRY6VbKv8l /gihrtx7A6pfGle2Uec17mRnOrDeiZEsM9EwRdsCKZe81OUpaezTsBJX2gnWOQch8p6v 5UP2mkNmKCBcZnsagNYVygg0y71x9nEE7OvWI= Sender: netfilter-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: netfilter@vger.kernel.org Dear Experts I am curious to know more about what FORWARD chain inbound and outbound actually mean. Example firewall set-up below: Internet --- Firewall --- PC Firewall has 2 interfaces: eth0 = External and eth1 = Internal >From what I can gather from the Netfilter website, all I need to do is create are inbound and outbound rules on the FORWARD chain. To allow inbound Internet access, I specify: FORWARD -i eth0 To allow outbound PC access, I specify: FORWARD -o eth1 The question is from whose perspective do you view what is inbound and what is outbound? For example, in the case of the Internet client, traffic flowing towards the firewall is indeed Inbound so naturally "FORWARD -i eth0" is required. However, isn't it also Outbound on eth1, given that it leaves interface eth1 to get to PC? Similarly, clients on the internal network think of their traffic as being outbound only, but when traffic is being "forwarded" from eth1 to eth0 heading for the Internet, isn't that traffic classed as Inbound on eth0? Do I need to create rules for this scenario also or is Netfilter handling these implied situations? Beginner questions so apologies in advance. Paddy.