Bandwidth 'depredation' revisited

Hi all :))

I've took a look at the documentation related to Traffic Control
and Class Based Queuing, but all of them seems to deal with upload bandwidth, so it won't solve my problem, which is that wget eats all my download bandwidth.

I know: downlink traffic cannot be shaped and Traffic Control is
for data WE send. So, am I missing something? Will my problem be solved and download bandwidth shared between apps thru Traffic Control or will I just get better interactive response?

I think that I'm missing something here, but I'm clueless...

Thanks in advance :)

Raúl

When you start a big download, you actually request a server to send as much data as possible to you. Quickly, the packet queues on your ISP's side gets filled up. If these queues are big (can hold many packets) you will see a rather high latency when trying to retrieve replys, since any pakcets (incl. ACK) will need first to enter the queue, and wait for their turn to be send to you.

The best solution would be to install some sort of traffic shaping on the remove side (you ISP), but that is often(/always) not a possible solution.

The second best solution is to simple drop packets comming in too quickly from the interface. By this, the sending machine will slow down transmission. The idea is to keep the queues at you ISP empty.

To do this you can use ingress scheduler.

Something like:
tc qdisc add dev eth0 handle ffff: ingress
tc filter add dev etc0 parent ffff: protocol ip prio 50 u32 \
match ip src 0.0.0.0/0 police \
rate 232kbit burst 10k drop flowid :1

The downside is, that this actually decreases the maximum download speed, but you can really feel the difference.

IIRC, All this was explained in the Advanced-Routing howto.
There is an example in it, which sets the ingress scheduler up. You can also take a look at the "wonder shaper" at http://lartc.org/wondershaper/.

Regards
Anders Fugmann

Rather than dropping packets, causing retransmits that eat into your bandwidth, you could try the new ECN bits. If you're downloading from a Linux box, it ought to slow down a bit when you claim to be suffering congestion.

ftp://ftp.isi.edu/in-notes/rfc3168.txt
http://www.faqs.org/rfcs/rfc3168.html
http://www.aciri.org/floyd/ecn.html
http://gtf.org/garzik/ecn/
http://www.tux.org/lkml/#s14-2

Yes - That would really be ideal.
Do you know how to enable ECN on the ingress filter, or which filter to use instead?

Anders

Try http://luxik.cdi.cz/~patrick/imq/index.html. Imq allows to shape incomming traffic with egres qdiscs.

Hi Anders :)

That's the point... I'll give it a try, then.

OK. Maybe a stupid question: will I need to mark the packages
with iptables in order to get them thru de ingress scheduler :?

Don't worry about that. I'll give it a try and compare results.

I missed this part, then. Well, I didn't read deeply the
different shapers...

Thanks a lot :)
Raúl

No. You can, but dont need to. The above lines match anything comming from eth0, and shapes it to 232kbit. Tweak the value to suit your needs.

Anders Fugmann

Does this work with 2.2 kernels? I've enabled CONFIG_NET_CLS_POLICE, but tc just barfs

RTNETLINK answers: No such file or directory

Shaping with CBQ works fine. Debian Woody, iproute 20010824-8.

Marius Gedminas

Q:      Why do mountain climbers rope themselves together?
A:      To prevent the sensible ones from going home.

You could also just delay trafic from certain IPs. Or even better, you could postpone acknowledgedments until you get the right distribution.

I know routers that do the former to gain fair download on shared internet connections, but the second would be a lot nicer.