[LARTC] simple TOS based setup vs more complex ones

[Gustavo Homem]

Hi Martin,

On Mon, Jul 10, 2006 at 03:45:49PM -0500, Martin A. Brown wrote:
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> Hello Gustavo,
> 
>  : After reading section 9 of LARTC it seemed to me that a pure TOS 
>  : based QoS setup with be sufficient for a small newtork. 
>  : Interactive packets could have the highest priority, second 
>  : highest for DNS and small HTTP packets and lowest prio for all 
>  : others.
>  : 
>  : The advantage is that, the setup would be simply a couple of 
>  : iptables lines, because the default pfifo_fast qdisc already 
>  : implements priorities.
> 
> In your proposed system, is still possible for a flood of DNS 
> queries to cause queue depths upstream (and queue depths translate 
> directly to queue backups and delays).

Sure, but I am talking about a simple setup that works for small networks. In such cases there won't be DNS floods, unless someone really wants to generate one.

> 
>  : For this case, what is the recommended way to limit the outgoing 
>  : rate to ensure that nothing is queued on the modem?
> 
> The answer depends on what you are trying to do.  Consider HTB 
> and/or HFSC.  Although you might find that TBF is sufficient, you 
> are already talking about ToS, so TBF probably won't cut the 
> mustard in your situation.
> 
>  : Can this be done with pfifo_fast?
> 
> Not really.  

So the priorities are useless in real world with pfifo_fast, is that it? This is bit surprising, IIUC. This is why I asked.

> Although, the actual qdisc proposed is different, 
> please see this recent exchange [0] about prio qdisc.
> 
> If you are using a work-conserving qdisc (i.e., a qdisc that 
> performs no shaping), you'll not really be able to guarantee 
> anything about the quality of traffic from one point to another.  
> In order to offer some sort of guarantees on any link, your device 
> must be the bottleneck.  This requires shaping or, at least, some 
> sort of non-work-conserving qdisc.
> 

What I was initially looking for was just TOS marking + plus simple interface throtlling, i.e, the simplest form of shapping. If it can't be done with pfifo_fast, my next idea was something like:

	tc qdisc add dev eth0 root handle 1: htb default 10
	tc class add dev eth0 parent 1: classid 1:1 htb rate 7000kbps ceil 7000kbps
	tc class add dev eth0 parent 1:1 classid 1:10 prio

	+

	iptables rules for setting TOS values

Is this right? This seems to be similar to what you proposed here:

http://mailman.ds9a.nl/pipermail/lartc/2006q2/019138.html

For a not so simple approach but which seems to be working well, I have an adaption of Dan Singletary's script here:

http://downloads.angulosolido.pt/QoS/

It uses directly HTB on both directions, for a setup with only 2 network interfaces which is very common (no kernel patching is needed).

Do you want to comment?

Still, I want to test the simplest possible solution and see how far one can go with only a few lines of bash, for both practical and pedagogical purposes. I think it's important to have a simple solution that works for typical scenarios (2 interfaces, linux router with NAT) on stock kernels. **

Best regards
Gustavo

** nothing wrong about patching and compiling kernels, but it brings maintenance overhead everytime there is system upgrade for whatever reason

-- 
Angulo Sólido - Tecnologias de Informação
http://angulosolido.pt

> Good luck,
> 
> - -Martin
> 
>  [0] http://mailman.ds9a.nl/pipermail/lartc/2006q2/019130.html
>      http://mailman.ds9a.nl/pipermail/lartc/2006q2/019138.html
>      http://mailman.ds9a.nl/pipermail/lartc/2006q2/019143.html
>      http://mailman.ds9a.nl/pipermail/lartc/2006q2/019158.html
> 
> - -- 
> Martin A. Brown
> http://linux-ip.net/
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