Here's the question bank on all the computer networks topics.
Consider routing table of an organizations router shown below:Subnet Number Subnet MaskNext Hop12.20.164.0255.255.252.0R112.20.170.0255.255.254.0R212.20.168.0 255.255.254.0 Interface 012.20.166.0255.255.254.0Interface 1 default R3Which of the following prefixes in CIDR notation can be collectively used to correctly aggregate all of the subnets in the routing table?
The correct answer is option 1, option 3.Concept:CIDR notation:CIDR notation (Classless Inter-Domain Routing) is an alternate method of representing a subnet mask. It is simply a count of the number of network bits (bits that are set to 1) in the subnet mask.Explanation:IP prefixes can be aggregated, by merging specific, long prefixes into broader, smaller ones. If filtering is done, we may delete those specific prefixes from the forwarding table and save state information. This is a way to improve routing scalability.1. 12.20.164.0 12.20.10100100.00000000255.255.252.0255.255.11111100.00000000 2. 12.20.170.0 12.20.10101010.00000000255.255.254.0255.255.11111110.000000003.12.20.168.0 12.20.10101000.00000000255.255.254.0255.255.11111110.00000000 4. 12.20.166.0 12.20.10100110.00000000255.255.254.0255.255.11111110.00000000Subnet (2) and (3) can be aggregated.12.20.101010 10.0000000012.20.101010 00.00000000----------------------------------------------------12.20.101010 00.00000000 = 12.20.168.0/22Subnet (1) and (4) can be aggregated.12.20.101001 00.0000000012.20.101001 10.00000000----------------------------------------------12.20.101001 10 .00000000 = 12.20.134.0/22Hence the correct answer is option 2, option 4.
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