[nsp] dscp setup

[Oliver Boehmer (oboehmer)]

> I'd like to submit this config for review. My goal is to have outbound
> latency sensetive traffic(acl 101) and outbound lantency in-sensetive
> traffic(acl 102) get marked w/ dscp values on the internal interface,
> fa0. 
> 
[...]
> 
> Can anyone spot anything wrong with this? I'm worried about QoS. DSCP
> should give prefence to acl 101 but I'm not sure as this is my first
> foray into dscp.

Your approach seems to achieve what you have in mind. I'd still worry
about your class-default, i.e. all traffic not matched by either one of
your ACLs. Based on your policy you don't give any treatment to this
traffic. By default you'll only allocate 75% of the interface bandwidth
to your two classes, so class-default will share the remaining 25% with
all other traffic like routing updates/keepalives/etc. Please make sure
if this is what you want/need. The 75% value can be changed using the
max-reserved bandwidth interface comment.

Please also bear in mind that allocating such a large priority queue can
really slow down your other traffic.

> Should I just dump DSCP and opt for GTS?

You're mixing terms/concepts here. DSCP by itself is way of marking, GTS
is queuing. With your config approach you are using DSCP for marking and
CBWFQ/PQ for queuing, and this is what I'd do.

> Also once packets marked w/ DSCP leave my network - do routers further
> downstream reset those bits to 0? If thats the case Dscps value goes
> down signifigantly.

Well, this depends on the other routers' configuration/policy. If they
reset the dscp to zero, there is not too much point for you setting the
dscp value in the first place, and you can simplify your config by
getting rid of the inbound policy map (setdscp) and its classes and
configure

policy-map manage
class sensetive
priority percent 70
class insensetive
bandwidth remaining percent 30

on your outgoing interface.
 
> Thanks for any feedback, I've found QoS to be very foggy...

I hope I was able to clear the fog a bit ;-) I agree QoS/DiffServ can
get quite complex..

	oli