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5Describe 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.
Egress blocking can occur for frames leaving the Frame Relay network going to the main site, because the sum of the access rates of the 20 sites exceeds the access rate at the main site. Egress blocking occurs for packets leaving the Frame Relay network going to an individual remote site, because the access rate at the main site exceeds the access rate at each remote site.
6If 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?
Because Tc = Bc/CIR, the answer is 16,000/256,000, or 62.5 ms.
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.
7Define the terms Tc, Bc, Be, and CIR.
Tc: Time interval, measured in milliseconds, over which the committed burst (Bc) can be sent.
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.
8Explain the goal of the Da and Dc debt processes when using CAR.
CAR attempts to reduce congestion by getting the senders of the traffic to slow down, similar to WRED.
9Describe the concept of traffic-shaping adaption, explaining the two triggers that cause shaping to adapt.
Adaption causes the shaper to reduce the shaping rate during congestion. Shaping can react to frames with the BECN bit set, or to Cisco Foresight congestion messages.
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16Compare and contrast the use of the class-map and map-class commands in terms of how each is used by FRTS and CB shaping.
FRTS uses map-class to create a common set of shaping parameters, which are then applied to an interface, subinterface, or VC. FRTS does not use the class-map command for shaping. Likewise, CB shaping does not use the map-class command. It does, however, use the class-map command for defining classification options. Interestingly, FRTS can use the class-map command indirectly, when using CBWFQ or LLQ. (Example 5-9 shows a sample configuration.)
17Describe 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.)
You can use the service-policy command inside map-class configuration mode.
18Explain 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.)
CB shaping requires a policy map, with class commands inside the policy map. Inside class configuration mode inside the CB shaping policy map, the service-policy command can refer to another policy map, which could enable LLQ for the class.
19Explain 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.)
GTS does not support LLQ as one of its shaping queues.
20GTS has been configured under subinterface s0/0.1. What show command lists statistics for GTS behavior just for that subinterface?
show traffic-shape statistics interface s0/0.1
21DTS has been configured under subinterface s0/0.1. What show command lists statistics for DTS behavior just for that subinterface?
show policy-map interface s0/0.1
22CB shaping has been configured under subinterface s0/0.1. What show command lists statistics for CB shaping behavior just for that subinterface?
show policy-map interface s0/0.1
800 Appendix A: Answers to the “Do I Know This Already?” Quizzes and Q&A Sections
23FRTS has been configured under subinterface s0/0.1. What show command lists statistics for FRTS behavior just for that subinterface?
show traffic-shape statistics interface s0/0.1
24Which of the traffic-shaping tools can be enabled on PPP interfaces?
GTS, DTS, and CB shaping.
25Which of the traffic-shaping tools can be enabled on each VC on a Frame Relay multipoint subinterface?
FRTS.
26Which of the traffic-shaping tools support adaptive shaping?
FRTS, GTS, DTS, and CB shaping.
27For which of the traffic-shaping tools does IOS perform shaping processing on 7500 VIP cards?
DTS.
28Which of the traffic-shaping tools can classify traffic to shape subsets of the traffic on a subinterface?
GTS, DTS, and CB shaping.
29Which shaping tools do not support WFQ and PQ to be used for the shaping queues?
GTS, CB shaping, DTS.
30Which 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?
FRTS.
Traffic-Policing Tools
31Explain the use of the continue keyword as part of CAR policing actions, and the feature CAR provides through the keyword.
CAR allows nested, or cascaded, rate-limit commands. A single packet can match the classification logic of a rate-limit command, but if the action includes the continue keyword, the packet is compared to any additional rate-limit commands, until another one is matched. CAR supports the ability to police a superset of the traffic, and then police a subset of the traffic at a different rate, using the continue keyword.
32CAR has been configured under subinterface s0/0.1. What show command lists statistics for CAR behavior just for that subinterface?
show interfaces s 0/0.1 rate-limit