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+3 votes
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Consider a subnet with 720 routers. If a three level hierarchy is choosen with 8 clusters, each containing9 regions of 10 routers, then total number of entries in the routing table is_______

  1. 25
  2. 27
  3. 53
  4. 72
asked in Computer Networks by (117 points) | 2.2k views

2 Answers

+7 votes

If there is no hierarchy each router needs 720 routing table entries. if the subnet is divided into 24 regions of 30 routers each router needs 30 local+ 23 remote entries for a total of 53 entries.If a 3 level hierarchy is chosen with 8 clusters each containing 9 regions of 10 routers then each router need 10 entries for local router 8 entries for routing to other regions within its own cluster and 7 entries for distant cluster for a total of 10+8+7 =25 entries

answered by Boss (49.6k points)
0
Sir how did you get  7 entries  ?  can you draw a pic ? thanks
0
Yes please explain about 7 entries ?
0 votes
Answer could be like this:

We know that

Cluster * Region * Routers = 720

We use the given formula to find minimum size of Routing table:

( Cluster-1 ) + ( Region-1 ) + Routers

Therefore, here also Cluster = 8, Region = 9 & Routers = 10

( 8-1 ) + ( 9-1 ) + 10 = 7 + 8 + 10 = 25.
answered by (141 points)

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