Consider a subnet with 720 routers. If a three level hierarchy is chosen with…
2015
Consider a subnet with 720 routers. If a three level hierarchy is chosen with 8 clusters, each containing 9 regions of 10 routers, then total number of entries in the routing table is _______
- A.
25
- B.
27
- C.
53
- D.
72
Attempted by 96 students.
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Correct answer: A
Solution:
Check total routers: 8 clusters × 9 regions per cluster × 10 routers per region = 720 routers (matches the problem).
Count routing-table entries for a single router using the three-level hierarchy:
Other routers in the same region: 10 - 1 = 9
Region-level entries for the other regions in the same cluster (aggregated): 9 - 1 = 8
Cluster-level entries for the other clusters (aggregated): 8 - 1 = 7
One aggregated/default entry to summarize remaining destinations = 1
Total entries = 9 + 8 + 7 + 1 = 25