Exam 400-007 topic 1 question 105 discussion

Please take care about the usage of Scavenger traffic. We don't want to limit the traffic all the time. CBWFD should be used mention in the link: https://www.ciscopress.com/articles/article.asp?p=357102&seqNum=5

we want to limit, therefore it has to be policed

limit during congestion

A is correct. Class-based traffic policing is used to enforce a bandwidth limit on a specific traffic class.

We need to limit the scavenger traffic to 2Mbps, so we need policing. CBWFQ can guarantee a min bandwidth per queue only.

Outbound traffic (towards the SP) has to be shaped, inbound traffic (at the SP level) has to be policed

Answer: C https://www.ciscopress.com/articles/article.asp?p=357102&seqNum=5 See 2nd bullet point: Scavenger traffic should be assigned the lowest configurable queuing service; for instance, in Cisco IOS, this means assigning a CBWFQ of 1 percent to Scavenger.

in the above question, it says "must use a QoS technique that limits the scavenger traffic to 2 Mbps, which helps avoid over subscription of the link during times of congestion". The engineer should not limit the traffic to 2Mbps all the time but only during congestion. Hence the engineer should use CBWFQ to allocate the non-scavenger traffic 18Mbps bandwidth and leave 2Mbps for the scavenger traffic. This way scavenger traffic is only limited during the congestion.

limit scavenger traffic during times of congestion

CBWFQ geurentees minimum bandwidth, but there maximum limit is 2 mbps, so policing, option A fits best. "CBWFQ is a scheduling mechanism used to provide a minimum bandwidth guarantee to traffic classes during times of network congestion at an interface. Each of the CBWFQ queues is assigned a weight, and the packets are served from the queues based upon the weight of the queue." https://www.oreilly.com/library/view/implementing-cisco-networking/9781787121782/12fad012-cdd3-4a99-9d27-41a053326b71.xhtml#:~:text=CBWFQ%20is%20a%20scheduling%20mechanism,the%20weight%20of%20the%20queue.

ans is B. traffic shaping is a QoS technique that can be used to control the rate of traffic sent to or from a network device.