[rbak-nsp] redback-nsp Digest, Vol 36, Issue 8

[Ian Calderbank]

David,

> Since I'm only interested in shaping, I may reduce this to a single queue
in order to save card resources, since as you can see from my example, they
all have the same weight :)

Use a min of two. One for network maintenance (i.e. ppp keepalives) at
higher priority one for subscriber-data at lower. With one shaped queue,
your subscribers can accidentally DOS' themselves by downloading so much
they get a constant full single queue, ppp keepalives get dropped on egress,
they get disconnected due to a keepalive drop :-(.

>     We use both:  in some places we actually have subscribers with 
> metering (for downstream remarking), policing (for upstream 
> remarking), and pwfq all on the same subscriber.  The box will mark 
> ("meter") downstream traffic & then queue it on the same subscriber all
day long.

> According to Ericsson, metering is occuring on egress, perhaps after the
sub is encapsulated in the tunnel headers, this perhaps explains why
"propagate qos to l2tp" was so broken (see my earlier posts)

For sure metering is on egress. This is a good one to walk through in a lab
with the different options on and off to make sure you understand it (and
check where the bugs are!). There is a complex relationship between mark
dscp , mark PD, propagate (or not), ingress and egress marking.  You also
have the option of egress marking on the subscriber circuit versus marking
on the circuit carrying the l2tp trunk.

> So I guess it is only possible to use policing policies for L2TP
subscribers, unless you have evidence of this working with metering on your
kit? (I dont know if you use internal DP like I want to or not)

I've deployed metering + queuing both on l2tp subs for sure.  {  However
those configs were developed for / are property of another isp which I was
contracted to, so lifting and posting that config would be unethical :-) }.
You just have to look carefully about which direction ingress vs egress
marks what field and be aware of what the defaults do particularly with the
PD bits.

ta
Ian