Cisco QoS FAQ: Traffic Policing and Shaping
Q1. Explain the points during the process of a single router receiving and forwarding traffic at which shaping and policing can be enabled on a router.
Q2. Compare and contrast the actions that shaping and policing take when a packet exceeds a traffic contract.
Q3. Compare and contrast the effects that shaping and policing have on bandwidth, delay, jitter, and loss.
Q4. Describe the typical locations to enable shaping and policing in an internetwork.
Q5. Describe the reasons behind egress blocking in a Frame Relay network with a T1 access link at the main site, 128-kbps access links at each of 20 remote sites, with 64-kbps CIR VCs from the main site to each remote site.
Q6. If a router has a shaping tool configured, with a shaping rate of 256 kbps, and a Bc of 16,000 bits, what Tc value does the shaping tool use?
If a router has a shaping tool configured, with a shaping rate of 512 kbps, and a Be of 16,000 bits, what Tc value does the shaping tool use?
Tc is not calculated based on Be, so you cannot know the answer with this limited amount of information. The formula to calculate Tc is as follows: Tc = Bc/CIR, where CIR is the shaping rate. If you know Bc and CIR, you can calculate the Tc value.
Q7. Define the terms Tc, Bc, Be, and CIR.
Bc: committed burst size, measured in bits. This is the amount of traffic that can be sent during every interval Tc. Typically also defined in the traffic contract.
Be: Excess burst size, in bits. This is the number of bits beyond Bc that can be sent in the first Tc after a period of inactivity.
CIR: committed information rate, in bits per second, defines the amount of bandwidth that the provider has agree to provide as defined in the traffic contract.
Q8. Explain the goal of the Da and Dc debt processes when using CAR.
Q9. Describe the concept of traffic-shaping adaption, explaining the two triggers that cause shaping to adapt.
Q10. Describe the difference between interface output queues and shaping queues, and explain where the queues could exist on a router with 1 physical interface and 20 subinterfaces.
Q11. What do the following intialisms stand for? FRTS, GTS, DTS, and CB shaping
Q12. List the command, with the correct syntax, that sets a shaped rate of 128 kbps, a Bc of 8000, and a Be of 8000, when using GTS. Do not assume any defaults; explicitly set the values in the command.
Q13. Along with the class-map, policy-map, and service-policy commands, CB shaping requires one specific command that actually sets values used for the shaping function. List the command, with the correct syntax, that sets a shaped rate of 128 kbps, a Bc of 8000, and a Be of 8000, when using CB shaping. Do not assume any defaults; explicitly set the values in the command.
Q14. Along with the class-map, policy-map, and service-policy commands, DTS requires one specific command that actually sets values used for the shaping function. List the command, with the correct syntax, that sets a shaped rate of 128 kbps, a Bc of 8000, and a Be of 8000, when using DTS. Do not assume any defaults; explicitly set the values in the command.
Q15. Many commands are needed to configure FRTS, but the actual shaping parameters, such as CIR and Bc, are set under the map-class frame-relay command. List the map-class subcommands, with the correct syntax, that sets a shaped rate of 128 kbps, a Bc of 8000, and a Be of 8000, when using FRTS, and using multiple commands. Do not assume any defaults; explicitly set the values in the commands.
16 Compare and contrast the use of the class-map and map-class commands in terms of how each is used by FRTS and CB shaping.
Q17. Describe the context inside the configuration mode under which the service-policy command can be used to enable LLQ on an FRTS shaping queue. (“Context” means what part of configuration mode—for instance, global-configuration mode, interface configuration mode, and so on.)
Q18. Explain the context inside the configuration mode under which the service-policy command can be used to enable LLQ on a CB shaping queue. (“Context” means what part of configuration mode—for instance, global-configuration mode, interface configuration mode, and so on.)
Q19. Explain the context inside the configuration mode under which the service-policy command can be used to enable LLQ on a GTS shaping queue. (“Context” means what part of configuration mode—for instance, global-configuration mode, interface configuration mode, and so on.)
Figure: Sample Network Used for GTS Configuration Examples
Q20. GTS has been configured under subinterface s0/0.1. What show command lists statistics for GTS behavior just for that subinterface?
21. DTS has been configured under subinterface s0/0.1. What show command lists statistics for DTS behavior just for that subinterface?
Q22. CB shaping has been configured under subinterface s0/0.1. What show command lists statistics for CB shaping behavior just for that subinterface?
Q23. FRTS has been configured under subinterface s0/0.1. What show command lists statistics for FRTS behavior just for that subinterface?
Q24. Which of the traffic-shaping tools can be enabled on PPP interfaces?
Q25. Which of the traffic-shaping tools can be enabled on each VC on a Frame Relay multipoint subinterface?
Q26. Which of the traffic-shaping tools support adaptive shaping?
Q27. For which of the traffic-shaping tools does IOS perform shaping processing on 7500 VIP cards?
28 Which of the traffic-shaping tools can classify traffic to shape subsets of the traffic on a subinterface?
Q29. Which shaping tools do not support WFQ and PQ to be used for the shaping queues?
Q30 Which shaping tools do not allow WFQ or LLQ to be used for the interface output queuing at the same time as the shaping tool is enabled on the same interface?
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