Where did you get the information that setting TOS with netfilter would affect prio classification ? From what I can see in the source, prio classifies by skb->priority which only inheirits a value from tos field during the forwarding process. I can recall skb->priority also beeing affected by setsockopt(IP_TOS) (besides SO_PRIORITY) but not by simply setting the tos field in the ip header.
Well, it just seemed obvious. One man's "obvious" being another's "bloody stupid idea", of course. Since prio is all based on tos bits it seems logical that changing those bits would have some effect.
I was partly just asking the simple question: are the TOS bits used to prioritise before netfilter gets its hand on them? The answer, from what you say, seems to be "yes". It seems a shame since its such an eligant and intuative way to do simple shaping of this sort
Best regards, Patrick
BTW: the netfilter CLASSIFY target from 2.6 or netfiler patch-o-matic can set skb->priority which is what you need.
This is for active duty so I'll not be running 2.6 until someone tells me it's stable...
Thanks,
Thomas
Thomas Worthington wrote:
Very simple setup: I have several machines, one of which (192.168.0.198) is used exclusively as a vnc client to a remote site. I want it to get priority over guff like email and web etc.
tc qdisc add dev eth1 root handle 1: prio tc qdisc add dev eth1 parent 1:1 handle 10: pfifo tc qdisc add dev eth1 parent 1:2 handle 20: pfifo tc qdisc add dev eth1 parent 1:3 handle 30: pfifo
iptables -t mangle -I OUTPUT -p icmp -s 192.168.0.198 -j TOS --set-tos 16
Effect: zero. All the vnc traffic from x.198 goes into 1:2.
I've tried all the tables (PREROUTE etc) to no avail. I even tried applying the TOS change to ALL traffice bound for eth1 (the outside line) and still saw no change in the queuing despite tcpdump showing that the tos bits were being set.
Why does this not work? It seems as if the priority is being set before iptables' mangle rules are applied.
Thomas Worthington
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