Explain ECMP and how it improves network throughput.

• A. ECMP uses multiple equal-cost routes to balance traffic, increasing throughput and redundancy via hashing across paths.
• B. ECMP uses a single path for all traffic.
• C. ECMP reduces routing table size.
• D. ECMP requires special hardware and never changes path selection.

Answer: (A)

ECMP uses multiple equal-cost paths to move traffic. When a router has more than one next-hop with the same metric, it can split the workload across those paths instead of pushing everything through a single route. A hashing mechanism looks at packet headers or flow identifiers and assigns each flow to a particular path, so packets from the same flow stay on the same route and don’t arrive out of order. This parallel use of several links increases the total available bandwidth, boosting network throughput, and it also provides redundancy because if one path or link fails, the others can continue carrying traffic. Topology changes or different hashing decisions can shift which paths are used over time, but the principle remains: multiple equal-cost options are leveraged to carry more traffic more reliably.

Using a single path would not achieve the same throughput benefits, and reducing routing table size isn’t the goal of ECMP. It also isn’t restricted to special hardware or guaranteed never to change; ECMP can be implemented in standard routing software, and the chosen paths can adapt as the network evolves.