QoS Lab Tips

  • Use MQC if FRTS is not an option and vice-versa
  • SPD or Selective Packet Discard seems very similar to RED, but uses terminology such as headroom. It is a hidden command and will need to refer to the DOCs
  • You can do service-policy within a policy-map , this is typically done under the policymap responsible for class class-default and is referred to as nested maps.
  • Make sure bandwidth matches value given in lab.
  • Bits per Interval, sustained or Burst (BC). To calculate the BC we need to know the TC. For example,  if the CIR is 384Kbps and we have 10 Time slices which is also 100ms (Tc), then the BC is CIR/TC which is 384000 (bits) / 10 = 38400
  • BC is 125ms (1/8th of a second) by default.
  • Bits per interval, excess or Burst Excess (BE). Generally the port speed – CIR, e.g. 512 – 384 = 128. then 128000 (bits) / TC (we are using 10 time slices at 100ms each) = 12800 (bits for excess).
  • If asked to adapt , use shape adaptive.
  • mincir is the value used as the lowest speed if a BECN / congestion notification is received
  • shaping allows queuing so can use shape-max-buffers 2000 (queue 2000 packets that goes over the shape average within, say, a match protocol class-map).
  • Verify QoS with show policy-map [expand with interface].
  • Use nbar if access-lists are not permitted and vice-versa (make sure ip cef is enabled for nbar).
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