Suppose you have the following routing table in your router. The Netmask identif

Question

Suppose you have the following routing table in your router. The Netmask identifies the bits we care about in the destination IP address. The Destination column identifies the values for the bits not masked out. Destination,Netmask,NextHop,Interface 0.0.0.0, 0.0.0.0, 100.10.1.1, eth0 128.148.0.0, 255.255.0.0, 128.148.0.1, eth1 128.148.32.0, 255.255.240.0, 128.148.32.1, eth2 128.148.34.128, 255.255.255.128, 128.148.34.129, eth3 What is the next hop for each of these addresses, given that you use longest-prefix matching? a) 128.148.34.192 b) 128.148.34.72 c) 128.148.1.1 d) 192.168.12.14 e) 128.148.38.15

Explanation / Answer

Solution:

1) 0.0.0.0, 0.0.0.0, 0.0.0.0/0

2) 128.148.0.0, 255.255.0.0, 128.148.0.0/16

3) 128.148.32.0, 255.255.240.0, 128.148.32.0/20

4) 128.148.34.128, 255.255.255.128, 128.148.34.128/25

a) 128.148.34.192

It matches 1, 2, 3 and 4

Since It has longest prefix match with 4

Next hop for 128.148.34.192 is 128.148.34.129 via eth3

b) 128.148.34.72

It matches 1, 2, 3

Since It has longest prefix match with 3

Next hop for 128.148.34.72 is 128.148.32.1 via eth2

c) 128.148.1.1

It matches 1 and 2

Since It has longest prefix match with 2

Next hop for 128.148.1.1 is 128.148.0.1 via eth1

d) 192.168.12.14

It matches only 1

so, Next hop for 192.168.12.14 is 100.10.1.1 via eth0

e) 128.148.38.15

It matches 1, 2, and 3

Since It has longest prefix match with 3

Next hop for 128.148.38.15 is 128.148.32.1 via eth2

Please, please upvote and ask your doubts in the comments.

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