[altq 291] Re: Ingress traffic shaping?

[George Uhl <uhl@mamba-e.gsfc.nasa.gov>]

Can't you use a traffic conditioner element to pass ingress traffic
coming over fxp0 to some acceptable rate and dropping the excess?

George

> 
> Karl Pielorz wrote:
> > We're running AltQ-2.1 on FreeBSD 3.3, and we have a config which sets up fxp0
> > to be an interface with a forwarding rate of 512kbs, i.e.
> > 
> > interface fxp0 bandwidth 512k cbq
> > 
> > Outoing traffic seems to be pretty much kept to this overall 512k limit...
> > However, incoming traffic (fxp0 connects via a cisco to a higher speed link,
> > i.e. 2mb) doesn't seem to be limited... I remember reading somewhere that
> > whilst you can schedule / shape outgoing traffic you can't do the same to
> > incoming traffic? 
> 
> That's right.
> 
> > - If this is true, surely the traffic coming 'in' from the
> > router is going to 'out' of the FreeBSD AltQ machine, and thus could be
> > shaped?
> 
> Managing incoming traffic is tricky:
>  - when congestion occurs, packets are dropped at the other side of
>    your bottleneck link.  you can't do much about it.
>  - if incoming traffic is all adaptive (e.g., tcp), there is a chance
>    to control incoming traffic to some extent.
>    but, for packet scheduling to work, packets need to be backlogged
>    in the queue.  
>    if the link is 512Kbps and you shape it to 512Kbps, packets are
>    never backlogged.
>    so, you have to shape it at a slightly lower rate in order to
>    create a bottleneck for the packet scheduler.
> 
> > ps. We do actually have valid reasons for wanting to shape 'incoming' requests
> > :-)
> 
> So does everyone :)
> 
> -Kenjiro