Re: want to randomly drop packets based on percent

[Stephen Hemminger <shemminger@osdl.org>]

O
> >>>>I wanted to insert artificial packet loss based on a percent so i found:
> >>>>network emulab qdisc could do it, so i compiled support into the kernel 
> >>>>and tried:
> >>>>tc qdisc change dev eth0 root netem loss .1%
> >>>>        
> >>>>
> >             ^^^^^^
> >
> >You need to do add not change. Add will set the queue discipline
> >to netem (default is pfifo_fast).  Change is for changing netem parameters
> >after it is loaded.
> >
> >  
> >
> bahhh I see... the wiki has "change" instead of add.  Now i'm running 
> into another problem, I have an XCP qdisc that I have already added via:
> tc qdisc add dev ath0 root xcp capacity 54Mbit size 500
> 

Wiki reads as a set of examples.  First uses, "add" after that "change".


> therefore when I also try to incorperate loss:
> tcq disc add dev ath0 root netem loss .1%
> 
> I get:
> RTNETLINK answers: File exists
> 
> Is it possible to use two qdiscs on the same interface?
> 

No, but netem is "classful" so you can put xcp inside netem.
Look at the token bucket example on the wiki.