[LARTC] pb with ingress policy

["Thomas SPECK" <thomas.speck@wanadoo.fr>]

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. 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.

Anyone having an idea ?

Kernel 2.4.19, iptables 1.2.6a.

Thank you
--
Thomas

_______________________________________________
LARTC mailing list / LARTC@mailman.ds9a.nl
http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/