Total of CBWFQ "priority percent" and "bandwidth percent" can't reach 100%?

gwhuang5398 · ‎11-17-2012

I have a 2811 router with the following QoS configuration. My intention is to have class INTERNET use whatever is left from other classes. Does this policy map accomplish this? I'm not sure because "show policy-map interface" doesn't show any bandwidth numbers for class INTERNET. Besides, there's also a class class-default in there too.

--------------

policy-map QOS
class VOICE
priority percent 20
class CONTROL
bandwidth percent 5
class VIDEO
bandwidth percent 30
class BUSINESS
bandwidth percent 30
random-detect
class INTERNET

int serial0/0/0
bandwidth 2000
max-reserve 100
service-policy out QOS

-----------------

I'm thinking to put a "bandwidth percent 15" command for class INTERNET. So it will use exactly all the remaining bandwidth. However IOS showed this error "Sum total of class bandwidths exceeds 99 percent". It only took the command "bandwidth percent 14", but in that case, the total only adds up to 99%.

My question is: (1) does the policy-map mean class INTERNET can use whatever is left from other classes? (2) if to have a bandwidth command for class INTERNET, is it IOS behavior to have total only to 99%?

Thanks

Reza Sharifi · ‎11-17-2012

Hi,

My question is: (1) does the policy-map mean class INTERNET can use whatever is left from other classes?

Yes, the remaining bandwidth (in this case 15 percent) goes to class-default (Internet) If class-default is not using it, than the other classes can use it.

Here is doc for more info:

http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a0080103eae.shtml

(2) if to have a bandwidth command for class INTERNET, is it IOS behavior to have total only to 99%?

The total sum should be at 100% not 99.

here is your sample config with Internet having 15%

policy-map qos

class voice

priority percent 20

class control

bandwidth percent 5

class video

bandwidth percent 30

class business

bandwidth percent 30

class internet

bandwidth percent 15

HTH

Joseph W. Doherty · ‎11-18-2012

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What you might be bumping into is a need for 1% of bandwidth being available for class-default (which is always present, even when not explicitly defined). Bandwidth allocation rules vary a little on your installed IOS, i.e. whether it's pre or post HQF.

Bandwidth statements set a "floor" bandwidth. Any unused bandwidth is available to outer non-LLQ classes. (If more than one class wants the excess available bandwidth, they will share it in the same ratios as their bandwidth statements are configured.)

(Note: LLQ classes are a little different as the priority statement defines an implicit policer.)

gwhuang5398 · ‎11-19-2012

I'm using IOS 12.4(24)T2. The router is 2811. The WAN interface is Frame-relay. Is 1% bandwidth required for class class-default in Cisco publications? I did a brief search of Cisco documentations but didn't find any.

In my config, is it precise to say "class INTERNET and class class-default will use whatever bandwidth is remaining from other classes"? When I tried "class INTERNET, bandwidth percent 15", IOS didn't accept it. If class class-default does require a minimum 1% bandwidth, this would make sense, because class-default can't be deleted.