GATE CSE 2004 | Question: 55

Question

The routing table of a router  is shown below:
$$\begin{array}{|l|l|l|} \hline \textbf {Destination} & \textbf {Subnet Mask} & \textbf{Interface}  \\\hline \text {128.75.43.0} &  \text{255.255.255.0} & \text{Eth$0$} \\\hline\text {128.75.43.0} &  \text{255.255.255.128} & \text{Eth$1$} \\\hline\text {192.12.17.5} &  \text{255.255.255.255} & \text{Eth$3$}\\\hline \text {Default} &  \text{} & \text{Eth$2$}\\\hline\end{array}$$
On which interface will the router forward packets addressed to destinations $128.75.43.16$ and $192.12.17.10$ respectively?

• A. Eth$1$ and Eth$2$
• B. Eth$0$ and Eth$2$
• C. Eth$0$ and Eth$3$
• D. Eth$1$ and Eth$3$

Comments

No two destination have same IP address but two IP address are in same Network.

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Two destination always have different IP address but more than one IP address can belong to same Network.

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Answer 1

Gabbar is right. But why do we take maximum mask?

Because the mask 255:255:255:128 is included in mask 255:255:255:0

i.e. 2nd destination is part of the 1st destination. So, if we forward directly to 2nd destiantion, the packet may reach the main destination faster.