How does iptables classify change skb priority

[Bhanu CV <vbhanu.mailinglists@gmail.com>]

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.

I had posted this same message on netfilter user mailing list but did
not get any responses. I am now posting it here hoping that the folks
on this mailing list would be able to help better.

Thanks in advance,
Bhanu