notes: LLQ

 

The LLQ feature brings strict priority queuing to CBWFQ. Strict priority queuing allows delaysensitive data such as voice to be dequeued and sent first (before packets in other queues are dequeued), giving delay-sensitive data preferential treatment over other traffic.

- LLQ adds the concept of a priority queue to CBWFQ, but without starving other classes.
- The LLQ provides a maximum bandwidth guarantee with low-latency, and optional burst capability.
- LLQ uses only one queue per QOS policy, does allow multiple queues.
- LLQ has a built-in congestion aware policer, preventing the starvation of non-priority traffic.
- The internal policer is ONLY applied during times of congestion, else LLQ traffic may use any excess bandwidth.
- During times of congestion, a priority class cannot use any excess bandwidth, thus any excess traffic will be dropped.
- But during times of non-congestion, traffic exceeding the LLQ is placed into the class default and is not priority "queued".
- This is why it is usually recommended to also add a "police" statement in the LLQ, so that priority traffic gets queued correctly or dropped.
- The queueing strategy will be 'class-based queueing' as with "show interface" command.

 

command:

- Shows the policy map configured with all the counters

sh policy-map interface {int}

- Shows the input and output queue size

- Shows the available bandwidth that can be assigned

sh queueing int {int}

class-map VOIP
match ip rtp 16384 16383

policy-map LLQ
class VOIP
priority {kbps} [burst {bytes}]

police cir {bps} bc {bytes} be {bytes

interface S0/0
service-policy output LLQ - Applies the queueing policy to the interface