[LARTC] problem with prio qdisc and TOS

Linux Advanced Routing and Traffic Control

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Hi Andreas,

I hope I have this right, based on my limited understanding of Linux QoS. 
If I'm wrong then I hope someone will correct me =)

>  If I just attach a PRIO qdisc on eth1(outgoing) will I be able to
> prioritise packets based on the TOS value.

You don't even need to do that, the default qdisc is pfifo_fast which also 
prioritises by TOS flags.

> The TOS value is set by a test application.

It can also be overridded by a Netfilter rule, if you want to force or 
change priority for certain types of packets.

> At very high data rates will the data stream with lower
> priority TOS value be starved because it cannot send out of packets from
> its band on eth1 interface?.

Yes, if there is not enough capacity to send on eth1 then lower-priority 
packets will be starved, will queue up until the queue is full and then 
get dropped.

> Does something be set in linux kernel so that kernel sets priority for
> packets according to TOS value.I guess this priorty will be used by PRIO
> qdisc(by default) to decide which band the packet belongs.

Yes, it happens by default, with the pfifo_fast qdisc.

Cheers, Chris.
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 / __// / ,__(_)_  | Chris Wilson -- UNIX Firewall Lead Developer |
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