cbwfq proportionally shared bandwidth

[Dennis Olvany]

I am troubleshooting an issue on a T1 where data latency spikes, but total bandwidth does not. I am interested in learning how proportional bandwidth sharing applies to the default class. The below document states, "If not all of the bandwidth is allocated, the remaining bandwidth is proportionally allocated among the classes, based on their configured bandwidth." I am unsure how this applies to a queue such as class-default, which lacks a bandwidth value.

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

Service policy:

policy-map out

class-map voice

  priority 768

class-map control

  bandwidth 256

class-map video

  bandwidth 512

class-map class-default

  fair-queue

[Juan Perez]

Hi Dennis,

Remaining BW will be allocated under class default but this can be used by other classes when unused, previous to HQF (12.4(20)T) class default could get starved because of the remaining classes, which will proportionally get the "unused" BW. Starting (12.4(20)T) class default will be guaranteed with at least 1% of the interface BW (unused traffic is still shared among other classes but you will have a minimum BW guarantee for default class).

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6558/white_paper_c11-481499.html

"Changes Related to Class-Default".

I hope this helps.