Dirk Tilger wrote:
> For the uploads, those dropped ACK packets make your peer think it is
> sending too fast, because it might be also that not the acknowledgement
> ("Yes I got it") of the message was dropped, but the message itself.
> The usual reaction is limiting its bandwidth. But that doesn't help,
> because you still utilize your download bandwidth fully. So it
> decreases sending power further...
Grab htb tools and set yourself up some QoS configs.
By proper queue's and packet classification you can *ensure* that acks going
upstream *never* get
dropped and get out the pipe first. This makes for great downloads :p)
QoS is a bit of black magic if you have never configured it previously, but the
combination of tc
for setting up your queues and iptables for classifying packets is immensely
powerful.
Here I have 4 queues.
-Acks
-SSH traffic / ICMP packets
-Other service related traffic - dns/ntp/...blah
-The rest (which generally is all my p-t-p traffic (this is a default catch all
bucket)
And the traffic is prioritised and sent out in that order.
In addition, I rate limit my outgoing at 10kbit/s slower than my maximum
acheivable speed.
Etisalat seems to control your bandwidth speed via external limiting rather
than limiting the actual
connection, so I can squirt about 512kbit/s upi my ADSL, but only about 380k/s
actually gets out to
the world, the rest gets dropped somewhere. By process of experimentation
(continuous pings from an
outside server) I determined that about 360k/s is about the maximum I can
squeeze through my pipe
without a) losing packets, and b) having huge laggy queues in the
modem/upstream router.
So by rate limiting my outgoing to 360k/s (not to bad for a 256k uplink!) I
never drop a vital
packet (I do drop p-t-p outgoing packets, but I do it before my modem) and I
ensure the fastest
round trip times for stuff that requires good latency (ntp/ssh).
QoS is certainly worth looking at if you have heavily utilised links. My ADSL
outbound is saturated
24/7 and with QoS I can ssh in from the outside world, tunnel VNC over ssh and
always have great
response times. without QoS it was almost unusable. In addition, I don't drop
outbound acks anymore
and my downloads are quicker.
As for bittorent.... I use azureus, and get great speeds if I'm connected to a
decent swarm. Most
stuff I download these days is botique and has small swarms, it can take
daaaaays/weeks/months to
get some stuff..
Having said that, I also use gtk-gnutella and might have the same file download
7 or 8 times
completely before a fully correct version happens, so bittorent has a lot going
for it in not
wasting bandwidth and ensuring a good download every time.
Perhaps QoS should be the topic of a future workshop session.
--
"Human beings, who are almost unique in having the ability
to learn from the experience of others, are also remarkable
for their apparent disinclination to do so." -- Douglas Adams
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