BCMSN QoS question

I am having trouble deciphering the following example config
it is supposed to demonstrate a max and min WRED threshold configuration
on a 1p2q2t line card I think

int g1/1
no ip address
wrr-queue bandwidth 50 75
wrr-queue queue-limit 100 50
wrr-queue random-detect min-threshold 1 50 70
wrr-queue random-detect max-threshold 1 75 100
wrr-queue cos-map 1 1 0 2
wrr-queue cos-map 1 2 3
wrr-queue cos-map 2 1 4
wrr-queue cos-map 2 2 6
priority queue cos-map 1 1 5 7
rcv-queue cos-map 1 1 0
switchport

I do not understand the follwoing 2 commands
wrr-queue cos-map 2 1 4
wrr-queue cos-map 2 2 6

It looks like the above thresholds explicitly configured for queue 1
how can you apply the threshold for queue 1 to queue 2?
or am I reading this wrong?

any help appreciated

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Comments

fonque

bumpity

techgirl321

That configuration is for Weighted Round Robin not WRED.
An example of Weighted Random Early Detection would be:
random-detect precedence 0 32 256 100
thats IP precedence 0 has a minimum threshold of 32 and a max threshold of 256 and 1/100 mark probability.
The example you provided is for weighted round robin cos mapping (changing the defaults)

The first number is the queue, the second number is the threshold, the third+ number(s) is the COS value. So here is how I am reading this:

wrr-queue cos-map 1 1 0 2 !map standard transmit queue 1 (low priority), drop threshold 1 to cos 0 or 2 marked frames
wrr-queue cos-map 1 2 3 !map standard transmit queue 1, drop threshold 2 to cos 3 marked frames
wrr-queue cos-map 2 1 4 !map standard transmit queue 2 (high priority), drop threshold 1, to cos 4 marked frames
wrr-queue cos-map 2 2 6 !map standard transmit queue 2, drop threshold 2 to cos 6 marked frames
And of course voice and routing is the ONLY traffic in the priority queue.

Per Cisco Documentation the defaults are:

•Receive queue 1/drop threshold 1 and transmit queue 1/drop threshold 1: CoS 0 and 1.

•Receive queue 1/drop threshold 2 and transmit queue 1/drop threshold 2: CoS 2 and 3.

•Receive queue 2/drop threshold 3 and transmit queue 2/drop threshold 1: CoS 4 and 6.

•Receive queue 2/drop threshold 4 and transmit queue 2/drop threshold 2: CoS 7.

•On 1p1q4t, 1p2q2t, and 1p3q1t interfaces, CoS 5 is mapped to the strict-priority queues.

In the example you provide they are just adjusting those maps to fit their needs.
Someone please correct me if I'm wrong here as I have only book/classroom experience with WRR.
Of course its 1 am so my accuracy is highly questionable.

lildeezul

yeah you are right....

i believe if there is only 1 threshold per queue. then the 1 is implied.

for instance, a cat 3550 with a 1p3q1t

the command could be wrr-queue cos-map 1 0 1 2

so this command says for queue 1, frames marked with a cos value of 0, 1, and 2 then they will be placed in queue 1.

see there wasnt the 1 1 0 1 2

the 1 is implied, so we go straight to 1 0 1 2.

hope this doesnt sound confusing

fonque

now i am totally confused. It is weight round robin, because that is when you would use weighted random early detection. You do not use WRED with shaped round robin.

however,
wred is configurable on a per queue basis. If that is the case explain what the "1" means in this command line.

wrr-queue random-detect min-threshold 1 50 70
wrr-queue random-detect max-threshold 1 75 100

does that "1" not assign these min and max thresholds specifically to queue 1 or am I wrong in thinking this?

lildeezul

the 1 is the queue id..

queue 1

it is saying... when queue 1 reached 50 percent full ,WRED turns on for threshold 1, and for threshold 2, WRED will turn on when queue 1 reaches 70 percent.

then it says, when queue reaches 75 percent congested it will tail drop all frames/packets.

fonque

lildeezul wrote:

the 1 is the queue id..

queue 1

it is saying... when queue 1 reached 50 percent full ,WRED turns on for threshold 1, and for threshold 2, WRED will turn on when queue 1 reaches 70 percent.

then it says, when queue reaches 75 percent congested it will tail drop all frames/packets.

that makes perfect sense.
however, taking into account your explanation of the wrr-queue random-detect command

what does this mean?

wrr-queue cos-map 2 1 4
wrr-queue cos-map 2 2 6

since the random-detect command is configured for queue id 1, then how can the cos-map for queue 2 point to threshold 1 and 2 which have been explicitly configured for queue 1, as described by your previous post?
shouldnt there also be a command like this included in my first example?

wrr-queue random-detect min-threshold "2" 50 70
wrr-queue random-detect max-threshold "2" 75 100

lildeezul

Ok i think your getting confused here.
The wrr-queue cos-map command is for congestion management using custom queuing, (weighted round robin)

with the wrr-queue random-detect command, this is a congestion avoidance tool using WRED.

with the congestion management command (wrr-queue cos-map 2 1 4 ) the meaning of this depends on the switch. the catalyst 3550 uses 1 threshold per queue, so the threshold is implied, therefore the command is saying for queue 2 place frames that are marked with a 1 and 4 into queue 2.

using a 6500 switch, which can have multiple thresholds, the command wrr-queue cos-map 2 1 4 interprets to be, for queue 2 , threshold 1 , place frames marked with a Cos value of 4 into queue 2 threshold 1.

hope this helps.;

waru

BCMSN no longer includes QoS according to http://www.cisco.com/web/learning/le3/current_exams/642-812.html

It is now included in ONT http://www.cisco.com/web/learning/le3/current_exams/642-845.html

Not sure if you meant ONT but thought I better mention it as I also wasted a bit of time on QoS while studying BCMSN.

lildeezul

technically its not, but i do not think its a waste of time to start studying this.

I really struggled with this topic until i finally got it. and i am glad i did.
becuase aftermy ISCW exam, i am going straight to Qos, and then ONT that way i can finish up my CCNP and only be two exams away from CCIP :]

its good learning material stay in there fonque

waru

It would be a waste of his time if he got to the exam expecting to see questions on QoS only to find there werent any!!

lildeezul

Time spent learning and studying new material, along with using brain power, Is not time wasted.
It is good to learn this material for future references, or just to increase his arsenal of knowledge... ect.

its good to know !

waru

lol yeah Im sure you would say that if you turned up to your next exam only to find a good chunk of what you had studied wasnt actually in the exam....

Might not be a waste of time in the long run but it would likely be a waste of money!! Unlikely to pass BCMSN studying the old subjects eh?

fonque

waru wrote:

lol yeah Im sure you would say that if you turned up to your next exam only to find a good chunk of what you had studied wasnt actually in the exam....

Might not be a waste of time in the long run but it would likely be a waste of money!! Unlikely to pass BCMSN studying the old subjects eh?

I am not studying for my exam, i am studying for my career. Any knowledge is good knowlege. I am not going terribly in depth with QoS but I want to stay on top of it since I have 6500/4500s to play around with in my lab at work.