Quick nested QoS question

mmaskart · ‎04-09-2008

Here is the config:

policy-map RATELIMIT

class-default

shape average 10000000

service-policy QOSPOLICY

policy-map QOSPOLICY

class VOICECLASS_MAP

priority xxx

class VIDEOCLASS_MAP

priority xxx

class class-default

fair-queue

interface FastEthernet0/0

service-policy output RATELIMIT

==========================

would this config shape the connection to 10Mb first then provide the specified LLQ within the nested policy-map?

According to the "shape average 10000000 ?" command: "Recommend not to configure it, the algorithm will find out the best value". Does that mean that traffic will burst as the router sees fit?

Thanks in advance for the help.

M

Joseph W. Doherty · ‎04-09-2008

"would this config shape the connection to 10Mb first then provide the specified LLQ within the nested policy-map?"

In theory it should. In practice it seems the shaper makes its own flow queues; haven't found specific information when it exactly pushes back into the child queues. (Somewhat similar issue to tx hardware FIFO queues need to overflow into defined software queues.)

"According to the "shape average 10000000 ?" command: "Recommend not to configure it, the algorithm will find out the best value". Does that mean that traffic will burst as the router sees fit?"

What this generally means is, allow the command to default the burst sizes. When working with realtime traffic, especially voice, the defaults might need to be reduced.

PS:

If you really wanted to limit 100 Mbps Fastethernet connection to 10 Mbps, I've found it better, if possible, to down the speed to 10 Mbps physically and just use the policy (QOSPOLICY) without a parent shaper.