[LARTC] tc causes errors on HTML downloads

[LARTC] tc causes errors on HTML downloads

[Jason Hunter]

LARTC - 

I have just started using tc in a closed capacity lab situation.  The
lab setup contains 20 machines (win 2000), each with 5 IP address,
downloading a sequence of HTML pages through HTTP.  The downloads are
accomplished by a simple browser simulator that is given a list of
pages.  It downloads a page and all its sub-components (frames, images,
etc.) and then moves on to the next page in the list.  There is a
separate browser simulator running on each IP address (a client).

These simulated clients talk to a web server through a Linux machine
setup up as a router (RedHat 7.3 - 2.4.18-3 stock).  I have configured
tc using the attached script to limit the bandwidth between each
simulated IP address and the server.  

When I run the test with 40 clients (40 of the 100 simulated IPs)
active, the simulated browser gives errors downloading the images in the
second page (of a two page list).  However, when tc is cleared (just
linux routing with no shaping) there are no errors.  If I reduce the
number of active clients to 4 or 5 then the errors also disappear.  

Can anyone suggest the cause of this behavior and how I might change my
tc configuration to avoid it?  Or any other suggestions on how to better
configure the queues to accomplish my goal?

Thanks for you responses, 

Jason Hunter
jthunter@ictcompress.com


----  Attached bash script ----------

#!/bin/bash

# add the top level queue to allow us to add other managing queues
tc qdisc add dev eth0 root handle 1:0 cbq bandwidth 100Mbit avpkt 1000
cell 8

# add a shaping queue for traffic to/from the LabNet (7 network)
machines individually
i=10
while (($i <= 200))
do
	j=0
	while (($j < 5))
	do
		k=$(($i+$j))
		tc class add dev eth0 parent 1:0 classid 1:$k cbq
bandwidth    \
100Mbit rate 1200bps weight 1 prio 8 allot 1514 cell 8 maxburst 100
avpkt  \ 1000 bounded 
		tc qdisc add dev eth0 parent 1:$k handle $k: sfq
		tc filter add dev eth0 parent 1:0 protocol ip prio 2 u32
match \
ip dst 192.168.7.$k flowid 1:$k
		tc filter add dev eth0 parent 1:0 protocol ip prio 2 u32
match \
ip src 192.168.7.$k flowid 1:$k

		j=$(($j+1))
	done

	i=$(($i+10))
done


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Re: [LARTC] tc causes errors on HTML downloads

[Martin Devera]

Probably you will have to do closer look (tcpdump
and tcptrace).
From my experiance I'd not believe CBQ much but without
closer expertise it is hard to say what's goin' on.
Also you tried to add IP adresses as both SRC and DST
which is nonsense to do on single interface. It seems
like if you don't understand that shaping shapes egress
traffic only.
devik

On Thu, 23 May 2002, Jason Hunter wrote:

>
> LARTC -
>
> I have just started using tc in a closed capacity lab situation.  The
> lab setup contains 20 machines (win 2000), each with 5 IP address,
> downloading a sequence of HTML pages through HTTP.  The downloads are
> accomplished by a simple browser simulator that is given a list of
> pages.  It downloads a page and all its sub-components (frames, images,
> etc.) and then moves on to the next page in the list.  There is a
> separate browser simulator running on each IP address (a client).
>
> These simulated clients talk to a web server through a Linux machine
> setup up as a router (RedHat 7.3 - 2.4.18-3 stock).  I have configured
> tc using the attached script to limit the bandwidth between each
> simulated IP address and the server.
>
> When I run the test with 40 clients (40 of the 100 simulated IPs)
> active, the simulated browser gives errors downloading the images in the
> second page (of a two page list).  However, when tc is cleared (just
> linux routing with no shaping) there are no errors.  If I reduce the
> number of active clients to 4 or 5 then the errors also disappear.
>
> Can anyone suggest the cause of this behavior and how I might change my
> tc configuration to avoid it?  Or any other suggestions on how to better
> configure the queues to accomplish my goal?
>
> Thanks for you responses,
>
> Jason Hunter
> jthunter@ictcompress.com
>
>
> ----  Attached bash script ----------
>
> #!/bin/bash
>
> # add the top level queue to allow us to add other managing queues
> tc qdisc add dev eth0 root handle 1:0 cbq bandwidth 100Mbit avpkt 1000
> cell 8
>
> # add a shaping queue for traffic to/from the LabNet (7 network)
> machines individually
> i\x10
> while (($i <= 200))
> do
> 	j=0
> 	while (($j < 5))
> 	do
> 		k=$(($i+$j))
> 		tc class add dev eth0 parent 1:0 classid 1:$k cbq
> bandwidth    \
> 100Mbit rate 1200bps weight 1 prio 8 allot 1514 cell 8 maxburst 100
> avpkt  \ 1000 bounded
> 		tc qdisc add dev eth0 parent 1:$k handle $k: sfq
> 		tc filter add dev eth0 parent 1:0 protocol ip prio 2 u32
> match \
> ip dst 192.168.7.$k flowid 1:$k
> 		tc filter add dev eth0 parent 1:0 protocol ip prio 2 u32
> match \
> ip src 192.168.7.$k flowid 1:$k
>
> 		j=$(($j+1))
> 	done
>
> 	i=$(($i+10))
> done
>
>
> _______________________________________________
> LARTC mailing list / LARTC@mailman.ds9a.nl
> http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/
>
>

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RE: [LARTC] tc causes errors on HTML downloads

[Jason Hunter]

Devik - 

Actually, I didn't realize that the shaping only shapes on egress.  That is interesting.  I assume this can be somewhat overcome by applying queues to both interfaces, however, this doesn't provide exactly the same simulation.  That is to say, if I am trying to simulate a bounded connection of 1200bps shared between the upload and the download (e.g. a modem) then there isn't a direct way to do this, unless you can filter traffic in both directions into the same queue?


>  tc class add dev eth0 parent 1:0 classid 1:$k cbq bandwidth    		   \
> 100Mbit rate 1200bps weight 1 prio 8 allot 1514 cell 8 maxburst 100 avpkt  \ 
> 1000 bounded

As for the errors, I think that I have tracked them down to the maxburst value of 100 in my second level cbq queues.  I adjusted this value to between 3 and 5, and got much better results.

- Jason 

 -----Original Message-----
From: 	Martin Devera [mailto:devik@cdi.cz] 
Sent:	Friday, May 24, 2002 4:27 AM
To:	Jason Hunter
Cc:	lartc@mailman.ds9a.nl
Subject:	Re: [LARTC] tc causes errors on HTML downloads

Probably you will have to do closer look (tcpdump
and tcptrace).
From my experiance I'd not believe CBQ much but without
closer expertise it is hard to say what's goin' on.
Also you tried to add IP adresses as both SRC and DST
which is nonsense to do on single interface. It seems
like if you don't understand that shaping shapes egress
traffic only.
devik



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http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/

RE: [LARTC] tc causes errors on HTML downloads

[Martin Devera]

Use IMQ. I will allow you it.

On Fri, 24 May 2002, Jason Hunter wrote:

> Devik -
>
> Actually, I didn't realize that the shaping only shapes on egress.  That is interesting.  I assume this can be somewhat overcome by applying queues to both interfaces, however, this doesn't provide exactly the same simulation.  That is to say, if I am trying to simulate a bounded connection of 1200bps shared between the upload and the download (e.g. a modem) then there isn't a direct way to do this, unless you can filter traffic in both directions into the same queue?
>
>
> >  tc class add dev eth0 parent 1:0 classid 1:$k cbq bandwidth    		   \
> > 100Mbit rate 1200bps weight 1 prio 8 allot 1514 cell 8 maxburst 100 avpkt  \
> > 1000 bounded
>
> As for the errors, I think that I have tracked them down to the maxburst value of 100 in my second level cbq queues.  I adjusted this value to between 3 and 5, and got much better results.
>
> - Jason
>
>  -----Original Message-----
> From: 	Martin Devera [mailto:devik@cdi.cz]
> Sent:	Friday, May 24, 2002 4:27 AM
> To:	Jason Hunter
> Cc:	lartc@mailman.ds9a.nl
> Subject:	Re: [LARTC] tc causes errors on HTML downloads
>
> Probably you will have to do closer look (tcpdump
> and tcptrace).
> >From my experiance I'd not believe CBQ much but without
> closer expertise it is hard to say what's goin' on.
> Also you tried to add IP adresses as both SRC and DST
> which is nonsense to do on single interface. It seems
> like if you don't understand that shaping shapes egress
> traffic only.
> devik
>
>
>
>
>

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