Some QoS Questions

[Thomas Schmitt]

Hello,

I need some help to understand differences in QoS policing configuration on XE platforms.

In each case I'm going to reserve 10% of 1gig interface with 150ms burst for EF/cos5 traffic and I'm using just 1 priority Queue (1P7Q3T)

1. police within priority command

policy-map 1P7Q3T
 class PRIO
  priority level 1 percent 10 1875000
end

2. Police within priority command, but without level

policy-map 1P7Q3T
 class PRIO
  priority percent 10 1875000
end

3. Police in class

policy-map 1P7Q3T
 class PRIO
  priority level 1
  police 100000000 1875000 conform-action transmit  exceed-action drop
end

4. policy in priority command with default burst (200ms) and police command (150ms burst) - what would take precedence?

policy-map MARKING
 class PRIO
  priority percent 10
  police 100000000 1875000 conform-action transmit  exceed-action drop
end

What are the differences between thouse policing methods?

Thanks

[Joseph W. Doherty]

Cannot say whether IOS-XE operates differently from IOS, but on the latter, the LLQ implicit policer only restricted traffic when traffic was queued. The "regular" policer processes traffic based on its actual transmission rate.

If you only have one LLQ defined, I suspect it doesn't matter whether the priority level is defined or not.

I would expect which ever policer has the lower burst size (with the same rate) would "trigger" first.

[Thomas Schmitt]

Hi,

how about BW Reservation for other classes?

For example if I say:

class VOICE-OUT
  priority level 1 percent 10

and  in other classes

 class CLASS-1-OUT
  bandwidth remaining percent 10

then I have 10% from 65%, don't I?

What do I have for the remaining 10%, if I use police command?

class VOICE-OUT
priority level 1 
police cir percent 10

[Joseph W. Doherty]

"then I have 10% from 65%, don't I?"

How to you come by 65%? I believe it's 10% of the remaining 90% and then that would only be true if you've defined the other classes to allocate 100% of the remaining.

"What do I have for the remaining 10%, if I use police command?"

I'm unfamiliar with that particular command syntax but suppose it would police at 10% of whatever it considers the CIR value.

[Thomas Schmitt]

Hi,

65% because = 75% max reserve-able - 10% for LLC

The question was, if I don't preserve 10% for LLC, but police it by 10% - it is the same for BW remaining percent command in other classes or not?

[Joseph W. Doherty · Accepted solution]

"75% max reserve-able"

Where do you find that documented? Very old CBWFQ use to have a default of 75%, but I recall there was a command to change that.

Anyway, understand the bandwidth command sets a ratio with other classes. So, for example, if you had bandwidth 25 percent it would get 1/4 bandwidth assuming the other 75% was allocated and also desired by other classes. If not, it would get ratio relative to other classes wanting bandwidth.

In the case of not defining the LLQ value, if there's not implicit policer then it would assume it operates like PQ. I.e. the priority class could preclude the other classes getting any bandwidth. But whatever they did get, like the PQ limited by a policer should be in the ratio of the class allocations. I.e. if the priority class operates without a limiter, than a class with 25% might not even obtain that.