Policy Map with a Service Policy

parians · ‎04-22-2010

Hi all, in regards to the configuration below, what exactly does the following two commands do:

class class-default
shape average 800000 8000

My interpretation is that the "class-default" applies the "shape average 800000 8000" shaping to the whole of the "SHAPE_VPN" policy. By doing this you have defined the bandwidth that the percentages in the SHAPE_VPN policy map uses. Is this correct?

My other question is, why do you need to put one policy map (SHAPE_VPN) in to another policy map (SHAPE) in order to apply a polcy map to an ADSL (ATM0) interface or a tunnel interface? Why can't the first policy map (SHAPE_VPN) be applied directly to the interfaces?

policy-map SHAPE_VPN
   class ROUTER
   bandwidth percent 5
   class MGMT
   bandwidth percent 10
   class DATA
   bandwidth percent 40
   random-detect dscp-based
   class class-default
   fair-queue
   random-detect

policy-map SHAPE
class class-default
shape average 800000 8000
service-policy SHAPE_VPN

Thanks everyone.

Giuseppe Larosa · ‎04-22-2010

Hello Parians,

this is an example of Hierarchical modular QoS:

the parent policy implements shaping for all packets and it is used to create a logical pipe at speed 800000 bps and invokes a child policy that is a scheduler, a Class Based Weighted Fair Queueing, that implements 4 queues for 4 traffic classes (including the default class)

The need for this nested policy maps come when you want to adapt to an effective speed that is lower than physical speed of outgoing interface (this is done by parent shape all policy) and at the same time you want to implement a queue system that provides differentiated QoS to some traffic classes (child policy).

Hope to help

Giuseppe