From mboxrd@z Thu Jan 1 00:00:00 1970 From: bossk Subject: ICMP fragmentation needed packets lost Date: Thu, 20 Mar 2008 18:13:35 +0100 Message-ID: <200803201813.36278.bossk@tyntec.biz> Reply-To: bossk@tyntec.biz Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline Sender: netfilter-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: netfilter@vger.kernel.org Hi, I have the following setup ------- ---------------- ----------------- ------------- ---------------- | B |--------| VPN-GW2 |=======| VPN-GW1 | --------| GW |--------| A | ------- ----------------- ------------------ ------------- ---------------- The server GW is in the same net (10.0.1.0/28) as VPN-GW via interface bond0 and connected to the same network (10.0.3.0/24) as server A with interface bond2. Server A can send packets to server B which can be reached through the VPN. Now the tricky part if server A sends a packet with a size of 1460 Bytes the VPN-GW1 sends an ICMP fragmentation-needed packet to A which is not passing the GW, if the FORWARD policy is set to DROP. I have enabled the following rules iptables -A FORWARD -i bond0 -o bond2 -j ACCEPT iptables -A FORWARD -i bond2 -o bond0 -j ACCEPT and specials rules iptables -A FORWARD -s 10.0.1.0/28 -d 10.0.3.0/24 -j ACCEPT iptables -A FORWARD -s 10.0.3.0/24 -d 10.0.1.0/28 -j ACCEPT If I set the FORWARD policy to ACCEPT then the ICMP fragmentation-needed packet is passing the GW. After I change the FORWARD policy to DROP that packet is not passing the GW. Has someone an idea why this happens? Thanks, bossk