Re: tc is giving an error: RTNETLINK answers: File exists

Linux Advanced Routing and Traffic Control

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On Sat, 2006-09-16 at 09:14 -0700, gypsy wrote:
> fourcentsshy wrote:
> > the script so I could examine what was really going on. For this device,
> > the error takes place on the third command. the command sequence take
> > place like this:
> > 
> > /sbin/tc qdisc add dev eth5 root handle 1: cbq bandwidth 1600Kbit\
> >  cell 8 avpkt 1000 mpu 64
> > 
> > /sbin/tc class add dev eth5 parent 1: classid 1:1 est 1sec 8sec cbq\
> >  bandwidth 1600Kbit rate 1500kbit allot 1514 maxburst 20 avpkt 1000\
> >  prio 0 bounded isolated
> > 
> > /sbin/tc qdisc add dev eth5 parent 1:1 handle 1:76 cbq\
> >  bandwidth 1600Kbit cell 8 avpkt 1000 mpu 64
> This says to me "cell", not "ceil".  That's a mistake.

I wish that were true. It would make this problem so much easier to
solve. The HTB classes use the ceil parameter, but CBQ qdiscs use the
cell parameter for packet transmission time calculations. The manual
says it has a reasonable default, but the working script I have didn't
shape properly until I played with it.

ATM, since I'm debugging the script, its setup to exit after the 3rd tc
command I've listed above. tc doesn't seem to care what handle I give
the second qdisc. I've tried many different handles and every time I get
the same error: 

RTNETLINK answers: File exists. 

I've even tried running those very same lines on different machines,
with different Linux distros on them. I keep getting the same error on
them as well. It would be helpful if the device let me know which file
it's talking about. The working script only adds CBQ classes to CBQ
classes. Is it possible that its forbidden to add a CBQ qdisc to a CBQ
class?

> 
> ==--snip--==

> One more thing.
> You can send your commands to a database (mysql or whatever).  Once
> disallowing duplicate records and again allowing dups.  The difference
> is the Bad Boy.

I do love mysql and work with it almost daily (great fun). I thought
about writing a customer database for the very reason you mentioned, but
dups are not the problem. I do have a working script that uses the same
resource file with no problems. It limits customer bandwidth nicely and
even uses the same method of choosing handles, but there is a minor
problem with load balancing. I'd very much like to fix that.

> 
> I use HTB not CBQ but I still think the parameter is "ceil" not "cell"
> and fixing that will help or solve.

When I first started playing with tc, I tried using HTBs because they
looked easier to work with. I couldn't get them to work, so I tried the
CBQs. They didn't work either. It turned out that one of our technicians
has installed an older version of Fedora on the gateway server and that
version of tc was broken. I upgraded it to FC4 and the script came
alive. Since the script was working, I didn't bother to switch back to
the HTBs (but I'm strongly considering doing just that). 

Thanks for your time. I guess I'll keep trying different things. 

Cheers,
William Murphy
Velocity Technologies, Inc.

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