Re: [LARTC] pb with ingress policy

[Stef Coene <stef.coene@docum.org>]

On Wednesday 07 August 2002 16:43, Thomas SPECK wrote:
> Hi !
>
> I have a single host which is connected via an 512kbit ADSL link to the
> net. I quite often use some realaudio application that uses some bandwidth
> and I want to avoid other traffic to scale that bandwidth down. So I used
> some classes (with htb) on imq0 device and applied some filters and it
> seems to work in most cases. However, there are some sites with which
> download is interrupted if bandwidth is limited. I tried to trace it down
> and did some simple test:
>
> modprobe imq numdevs=1
> tc qdisc add dev imq0 root handle 1: htb default 10
> tc class add dev imq0 parent 1: classid 1:10 htb rate 60kbit ceil 512kbit
> burst 15k tc qdisc add dev imq0 parent 1:10 handle 10: sfq perturb 10
> iptables -t mangle -A PREROUTING -i ppp0 -j IMQ --todev 0
> ip li set imq0 up
>
> So now all traffic is limited to 60kbit. 
You limit all traffic to 512 kbit with the ceil parameter, not 60 kbit.  The 
rate is used when you have 2 or more child classes with the same parent.

> If I use some particular site for
> downloading (with wget) I observe the following with tcpdump: At the
> beginning there is a huge burst (wget indicating something like 45 kbps)
> than speed decreases dramatically and achieves some equilibrium around
> 60kbit. Then for some reason after about 15 seconds my host sends FIN to
> the other site. Why ? ;-) Is that a problem with some queue being too full
> after the burst at the beginning ? I tried to play with the burst option
> and I also used the pmtu stuff (iptables -A FORWARD -p tcp --tcp-flags
> SYN,RST SYN -j TCPMSS  --clamp-mss-to-pmtu) without success.

Stef

-- 

stef.coene@docum.org
 "Using Linux as bandwidth manager"
     http://www.docum.org/
     #lartc @ irc.oftc.net
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