[LARTC] Fwd: police burst is mandatory?

[Andy Furniss]

Stas Oskin wrote:
> Hi.
> 
> I'm using the following filter from lartc "ultimate PPP" example:
> 
> tc filter add dev $DEV parent ffff: protocol ip prio 50 u32 match ip src \
> 
> 0.0.0.0/0 police rate ${DOWNLINK}kbit burst 10k drop flowid :1
> 
> It works fine, but when I remove the "burst 10k", I receive the following
> error:
> 
> "burst" requires "rate".
> Illegal "police"
> 
> AFAIK, burst is how many bytes can be transferred over "rate" up to "ceil"
> and is an optional parameter, but here it is mandatory? Also, shouldn't the
> "ceil" parameter absence make this parameter useless?
>

You are thinking of htb - for policer burst/buffer is required.

policers don't delay/shape/queue packets, they just drop overrate 
packets (when used with the drop param).

The burst is the length of a virtual buffer used to decide when to drop 
a packet, when it's "full" everything else gets dropped till enough time 
has passed for it to have enough room for the next packet, how much time 
depends on the rate.

It needs to be at least MTU (MTU+14 on eth) or the policer won't pass 
full size packets at all. If you make it too small, like making a real 
buffer too small - it won't be nice for tcp throughput.

Andy.