GATE | GATE MOCK 2017 | Question 51

A packet addressed to 128.48.64.0 came to a router having routing table as follows.
mock_3

Which interface will it be forwarded to ?

(A) A
(B) B
(C) C
(D) D


Answer: (B)

Explanation:



Logical AND operation between subnet mask and IP address gives the subnet ID.
a)128.48.64.0 & 255.255.255.0 = 128.48.64.0 which is not equal to the destination so the packet will not be forwarded to the interface A.

b) 128.48.64.0 & 255.255.128.0 = 128.48.0.0 so packet can be forwarded to B.
c) 128.48.64.0 & 255.255.0.0 = 128.48.0.0 so packet can be forwarded to C.

If two IP addresses match then the packet should be forwarded to the subnet with more number of 1’s in the subnet mask.

Hence, router will forward the packet to interface B.


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