Re: How does iptables classify change skb priority

[Patrick McHardy <kaber@trash.net>]

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.