[c-nsp] QoS - questions

[Jeff Tantsura]

Hi Oli,

My understanding was that at least in 12.0S one could configure explicit and
implicit policers so in case

class LLQ
 priority "bandwidth" 
policer would kick in only in case of congestion 
while in
class LLQ
 priority
 police "bandwidth" 
policer would drop any traffic above the bandwidth specified.

Thanks in advance for clarification.

Regards,,
Jeff

> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-
> bounces at puck.nether.net] On Behalf Of Oliver Boehmer (oboehmer)
> Sent: dinsdag 21 augustus 2007 9:33
> To: varaillon; cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] QoS - questions
> 
> varaillon <> wrote on Tuesday, August 21, 2007 9:20 AM:
> 
> > I have few questions about queuing on Cisco.
> >
> > 7200----HDLC/ISIS/TDP----26xx
> >
> > I have set-up QoS between the two Cisco routers mainly use to carry
> > voice traffic, as follow:
> >
> > Queue1: Voice Bearer    - LLQ        - priority bandwidth 55%
> > Queue2: Voice Signaling - CBWFQ      - bandwidth 10%
> > Queue3: Any IP traffic  - CBWFQ WRED - bandwidth 10%
> > Queue4: default
> >
> > * If my LLQ queue is full, can it borrow bandwidth from any other non
> > full queues including the default one?
> 
> No, "priority" implicitly configures a policer, and excess packets are
> dropped.
> 
> > * If any of my CBWFQ queues is full, can it borrow bandwidth from any
> > other non full queues including the default one?
> 
> Yes.
> 
> > If I use the command "max-reserved-bandwidth 90" on the serial
> > outgoing interface of both routers, and if I have the following
> > queues:
> >
> > Queue1: Voice Bearer    - LLQ        - priority bandwidth 70%
> > Queue2: Voice Signaling - CBWFQ      - bandwidth 10%
> > Queue3: Any IP traffic  - CBWFQ WRED - bandwidth 10%
> > Queue4: default
> 
> Usually you don't want to provision more than 50% of your BW for LLQ.
> Experience has shown that this can introduce some delay..
> 
> What would you put into the default class? See also comment below.
> 
> > What would happen in case of congestion:
> >
> > * Since I know that I have very little IP traffic, Queue 3,
> > guaranties that the TDP session won't go down, right?
> 
> well, since you enabled WRED, we could also drop TDP packets..
> 
> > * Since the default queue has the remaining 10% of the bandwidth,
> > HDLC and ISIS won't go down, right?
> 
> well, first of all you also want to reserve BW there, i.e. add
> "bandwidth percent 10" as well. Then check out
> http://www.cisco.com/warp/public/105/rtgupdates.html to see how your
> platform treats those packets.
> 
> > * So, in this case and despite Cisco advices on that matter, is it
> > safe to use the "max-reserved-bandwidth 90" command?
> 
> I would think so.
> 
> > * Do I risk to lose the serial link due to a lack of bandwidth?
> >
> > * Do I risk anything else?
> 
> No, looks good with the above changes..
> 
> 	oli
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