Alcatel-Lucent NRS II – Wide Area Network Services — Question 11

All links have 1Gbps unreserved bandwidth initially and all LSPs have the least-fill feature enabled. After the two LSPs have been signaled as shown, two new
LSPs are configured. LSP-3 is signaled first with 600Mbps reserved. LSP-4 is signaled after with 800Mbps reserved. All LSPs have the same setup and hold priorities. Which paths will CSPF choose for LSP-3 and LSP-4?

Answer options

• A. LSP-3 takes R1-R3-R5-R6 and LSP-4 takes R1-R2-R4-R6.
• B. LSP-3 takes R1-R2-R4-R6 and LSP-4 takes R1-R3-R5-R6.
• C. LSP-3 takes R1-R3-R5-R6 and LSP-4 has no available path.
• D. LSP-3 takes R1-R2-R4-R6 and LSP-4 has no available path.

Correct answer: C

Explanation

The correct answer is C because LSP-3 reserves 600Mbps and can take the path R1-R3-R5-R6, leaving only 400Mbps available. When LSP-4 attempts to reserve 800Mbps, it finds that no path can accommodate this request, resulting in no available path for LSP-4. The other options incorrectly suggest that both LSPs can be accommodated, which is not possible given the bandwidth constraints.