From mboxrd@z Thu Jan 1 00:00:00 1970 From: Patrick McHardy Subject: Re: How does iptables classify change skb priority Date: Tue, 01 Feb 2011 17:36:27 +0100 Message-ID: <4D48368B.6050906@trash.net> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: netfilter-devel@vger.kernel.org To: Bhanu CV Return-path: Received: from stinky.trash.net ([213.144.137.162]:45448 "EHLO stinky.trash.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751432Ab1BAQgc (ORCPT ); Tue, 1 Feb 2011 11:36:32 -0500 In-Reply-To: Sender: netfilter-devel-owner@vger.kernel.org List-ID: Am 01.02.2011 17:31, schrieb Bhanu CV: > Hi, > > I am trying to change the skb priority of the packets going out to a > particular destination. Then I use vlan set_egress_map to change the > vlan priority of the packet. This works as I want it to, the confusing > part is I do not know why it works! > > I use the following two commands: > > change the skb->priority (?) for the packets that I am interested in to 3: > iptables -t mangle -A POSTROUTING -d 192.168.10.75 -j CLASSIFY --set-class 0:3 > > change the vlan priority of the packet leaving over the vlan > vconfig set_egress_map eth4.2 3 3 > > This does send a packet on the wire with MAC layer priority of 3, > which is what I want. What I am trying to understand is the action > that iptables is taking. I do not have any class under the root qdisc > on eth4. The root qdisc has handle 0: > > It would be great if someone could explain how iptables is classifying > the packet in a way which changes the skb->priority of the packet. It simply changes the skb->priority value, which used by the VLAN driver to map to VLAN proprities. This is done by the VLAN driver internally and unrelated to qdiscs.