Configuring MDRR on Cisco 12000 series router

[kimyin-tay]

I am implementing QOS on a MPLS network. Cisco recommends to use MDRR for Cisco 12000 series routers.

Here is the Cisco url for the MDRR configuration example which i use.

Configuring MDRR and WRED on the Cisco 12000 Series Internet Router Using the Legacy CoS Syntax

http://www.cisco.com/warp/public/63/legacy_cos.html

I have extracted some portion of the above example,

Use the cos-queue-group command to define any WRED parameters:

random-detect-label <label> <minimum-threshold> <maximum-threshold> <mark-probability denominator>

Example

Random-detect-label 0 375 2423 1

!-- Min. threshold 375 packets, max. threshold 2423 packets.

!-- Drop probability at max. threshold is 1

I wish to know what criteria they use when selecting the minimum and maximum threshold ?

The above sample config does not indicate the link speed of the P to P router.

The customer setup is P router - P router, or P router to PE router is GigabitEthernet links.

For the above example, why was 375 and 2423 being used ? Any relation between these 2 values and the link speed ?

[Harold Ritter]

These numbers are taken from the following document and they are indeed related to Link BW:

http://www.cisco.com/en/US/partner/products/hw/routers/ps167/products_tech_note09186a0080094c00.shtml#topic2

Hope this helps,

[Harold Ritter]

According to internal information I was looking at, it would be more appropriate to follow the calculation explained in the following document to set the minimum threshold, maximum threshold and mark probability for WRED:

http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1824/products_feature_guide09186a0080087ae4.html#wp6484

Hope this helps,