Regarding to the config of QoS on policy-map

[Matsu1092]

Hello,
I use Cisco 1921, IOS 15.2(4)M4.
below is QoS configuration on this router.

!
policy-map QoS
 class Voice
     set precedence 5
   priority percent 10
class MCU
   set precedence 1
   bandwidth percent 50
class Management
  set precedence 2
bandwidth percent 10
  class class-default         <-------this
   bandwidth percent 1         <-------this
policy-map SHAPING
   class class-default
       shape average 4000000
       service-policy QoS
!

Regarding to "class class-default" and "bandwidth percent 1",  can default-class use only 40000 bps(1% of 4000000)?
or, this "bandwidth percent 1" is only minimum guaranteed bandwidth so default-class can user more than 1% bandwidth except congestion, is this correct?

[paul driver]

Hello
My understanding is in Hqos all BW is available for the other users classes, whatever is leftover from that 99% of the allocated BW goes to the class default otherwise the class-default has a min guaranteed 1% 

[Joseph W. Doherty]

Bandwidth statements guarantee a minimum.  With such a statement, alone, the class can use all 100% of bandwidth (this assuming there are no other classes of active traffic).

In your particular example, the 1% doesn't actually guarantee 1%, your minimum is more.

Why?  Because you've actually allocated the percentages of 10, 50, 10 and 1, which add up to 71% not 100%.

Your dequeuing ratios, for your non-LLQ (priority) traffic are 50:10:1.

So, for example if only your management class and default class wanted all the bandwidth they could obtain, it would be split 10:1, so class-default, would (at the moment) be guaranteed a minimum of about 9%. 

[Matsu1092]

I understood,
"bandwidth percent 1" means "minimum guaranteed bandwidth is 1% (actually 9%), not upper limit.

paul driver ,Joseph W. Doherty
Thank you very much for your help.

[Joseph W. Doherty]

First, in your OP, class-default upper limit is 100 percent, not 9 percent.

Second, in the example I described, upper limit is still 100 percent while the minimum (again in my example) is (about) 9 percent.

For bandwidth minimums to match your config, two conditions must be true/met.

First, your config must allocate 100 percent.  (Possibly, bandwidth classes might split unassigned bandwidth.  I don't recall seeing documentation on this.)

Second, all your classes must want their configured minimum or more.