Various questions regarding action parameters

Various questions regarding action parameters

[Phil Sutter]

Hi,

I'm in the process of writing man pages for tc actions. Sadly I wasn't
able to figure everything out by searching the web, grepping Git log or
reading kernel/iproute2 code. Therefore I present a number of open
questions here, hoping for you to help me work things out. Please feel
free to answer selected questions as well, any input is highly
appreciated.

connmark action
---------------
I struggle with the effect of the different branch targets. My
understanding so far is:

reclassify - restart classification by jumping back to the first filter
             on the same level.
pipe       - continue with the next action in line.
drop/shot  - drop packet without calling any further filters/actions

Is this correct so far? Could you please explain 'continue' and 'pass'
branches (and what distinguishes each from the others if questionable)?

Further, this action supports an 'index' option which seems to specify
the index at which this action is put into the list of actions attached
to the same filter. Is this correct? So is it just there as an
alternative to reordering the action list upon tc invocation? Or are
there other uses of that index?

police action
-------------
OK, this is lame: I failed to find out what distinguishes rate, peakrate
and avrate and what influence burst and mtu values have. That cell size
parameter to the latter was also completely obscure to me. I could
probably steal from tc-htb.8 for most of them, but writing things
without understanding them is usually not a good idea (actually
remembers me of some of my old professors at university ;).
Could you maybe point me to some documentation which applies to police
as well? Even though I finally understood what the rate precalculation
does, the respective kernel code looked pretty weird to me.

OK, that's it for now. (At least these are my 'XXX' entries right now,
review will probably arise more questions later.)

Thanks, Phil

Re: Various questions regarding action parameters

[Andrew Beverley]

On Fri, 2016-01-29 at 18:07 +0100, Phil Sutter wrote:
> I'm in the process of writing man pages for tc actions.

I can't help with your questions, but I just wanted to thank you for
taking on this much-needed task. Many thanks.

Andy

Re: Various questions regarding action parameters

[Martin A. Brown]

Hi Phil,

>I'm in the process of writing man pages for tc actions. Sadly I wasn't
>able to figure everything out by searching the web, grepping Git log or
>reading kernel/iproute2 code. Therefore I present a number of open
>questions here, hoping for you to help me work things out. Please feel
>free to answer selected questions as well, any input is highly
>appreciated.

[snip some good detail already]

>OK, that's it for now. (At least these are my 'XXX' entries right now,
>review will probably arise more questions later.)

I wish I knew more about the usage of 'action' in tc command-lines, 
but I do not.  I am also interested in your progress here, as this 
is an under-documented corner of the network stack.  Whenever I 
think of this section of the traffic control subsystem, I think of 
Jamal Hadi Salim, who seems to be one of the key players involved in 
its design (or maybe just usage).

Several years ago, when I was trying to grasp the system as a whole, 
there was not too much documentation on the 'action' component of 
the tc command line.

During last year's netdev 0.1 conference, it seems that there were 
two papers delivered that may provide some clues.  I just discovered 
today, when I looked for anything with Jamal's name on it.  I 
haven't read them yet, so if they are not directly relevant, then 
oops, apologies!  Here they are:

  http://people.netfilter.org/pablo/netdev0.1/papers/Linux-Traffic-Control-Classifier-Action-Subsystem-Architecture.pdf
  http://people.netfilter.org/pablo/netdev0.1/papers/Distributing-Linux-Traffic-Control-Classifier-Action-Subsystem.pdf

(It seems that there's a video of one of the presentations on the 
YouTube, as well.  Maybe I should view it.)

If you know of other sources of documentation other than the kernel 
and tc source, I would also be interested.

Good luck,

-Martin

-- 
Martin A. Brown
http://linux-ip.net/