Cisco
352-001 · Question #377
352-001 Question #377: Real Exam Question with Answer & Explanation
The correct answer is D: Adjust the OSPF auto-cost reference bandwidth on all routers.. Per-packet load balancing causes out-of-order delivery when equal-cost paths exist; adjusting the OSPF auto-cost reference bandwidth on all routers eliminates ECMP by making link costs unequal.
Question
Refer to the exhibit. After this new OSPF design with per-packet load balancing was implemented, Host A reported that large file downloads from Server A became slow and sometimes failed. The operations team discovered that packets are arriving out of order on R1. Which cost-conscious redesign action will fix the issue?
Exhibit
Options
- AUpgrade all links to 10 Gb/s.
- BAdjust MTU sizes to 1500 on all interfaces.
- CAdjust the OSPF auto-cost reference bandwidth on R4.
- DAdjust the OSPF auto-cost reference bandwidth on all routers.
Explanation
Per-packet load balancing causes out-of-order delivery when equal-cost paths exist; adjusting the OSPF auto-cost reference bandwidth on all routers eliminates ECMP by making link costs unequal.
Common mistakes.
- A. Upgrading all links to 10 Gb/s is not cost-conscious and may not eliminate ECMP if the upgraded links still compute equal OSPF costs.
- B. Setting MTU to 1500 on all interfaces does not affect OSPF cost calculations or path selection and will not stop per-packet load balancing.
- C. Adjusting the reference bandwidth only on R4 produces inconsistent cost calculations relative to the rest of the network, risking routing loops and suboptimal path selection without reliably eliminating ECMP.
Concept tested. OSPF auto-cost reference bandwidth and ECMP path selection
Reference. https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-1.html
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