Cisco
352-001 · Question #380
352-001 Question #380: Real Exam Question with Answer & Explanation
The correct answer is A: Shape traffic to 10 Mb/s on the CE router.. When a GigE CE interface connects to a 10 Mb/s MPLS service, traffic must be shaped to the contracted rate so QoS queuing operates correctly, and DSCP-based WRED should be enabled on AF classes to provide congestion avoidance for data traffic.
Question
A large retail bank is designing a unified communications solution to be deployed to its 200 branches. Its current network traffic consists of a web-based portal, Internet browsing, and general file server access. Each branch has between 15 and 20 users. The current WAN is based on Layer 3 MPLS and the customer manages its own CE routers. The WAN circuit interface to the service provider is Gigabit Ethernet, although the MPLS service that is contracted from the service provider is 10 Mb/s. The design is to use a DSCP-based four-class QoS policy to manage traffic demands. From the options below, which two QoS design options that should be implemented on the customer side will meet the requirement? (Choose two.)
Options
- AShape traffic to 10 Mb/s on the CE router.
- BPolice traffic to drop outbound traffic that exceeds 10 Mb/s.
- CClassify DSCP value EF for call signaling and voice packets, and place traffic in a strict priority
- DPriority queue traffic to demand up to 80% of total bandwidth.
- EEnable DSCP-based WRED on all AF classes.
Explanation
When a GigE CE interface connects to a 10 Mb/s MPLS service, traffic must be shaped to the contracted rate so QoS queuing operates correctly, and DSCP-based WRED should be enabled on AF classes to provide congestion avoidance for data traffic.
Common mistakes.
- B. Policing drops excess packets immediately without buffering, which bypasses the QoS queuing mechanism and introduces bursty packet loss for TCP flows rather than the smooth rate enforcement that shaping provides.
- C. DSCP EF (Expedited Forwarding) should be used only for voice bearer (RTP) traffic; call signaling should be marked AF31 or CS3, and combining both in a single EF priority queue removes the differentiation between signaling and media streams.
- D. Best practice limits the strict priority queue carrying EF-marked voice to no more than 33 percent of total bandwidth to prevent starvation of other classes; allocating 80 percent to priority queuing would starve all non-voice traffic.
Concept tested. CE QoS traffic shaping and WRED for contracted MPLS WAN
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