Question

Suppose computers A and B have IP addresses 10.105.1.113 and 10.105.1.91 respectively and they both use the same netmask N. Which of the values on N given below should not be used if A and B should belong to the same network?

• A. 255.255.255.192
• B. 255.255.255.0
• C. 255.255.255.224
• D. 255.255.255.128

Answer 1

The correct option is C 255.255.255.224

IP address of A = 10.105.1.113
=10.105.1.01110001
IP address of B = 10.105.1.91
= 10.105.1.01011011
For finding network address we take AND of IP
address with the netmask N. So we check one by one

(a) (i) $\begin{array}{c}\begin{array}{c}\mathrm{255.255.255.0}=N\\ \underset{–}{\mathrm{10.105.1.00000000}}\end{array}]TakingAND\\ \underset{–}{\mathrm{10.105.1.00000000}}\end{array}$

(ii) By taking and with B$\begin{array}{c}255\cdot 255\cdot 255\cdot 00000000\\ 10\cdot 105\cdot 1\cdot 01011011\\ \overline{10\cdot 105\cdot 1\cdot 000000000}\end{array}$

So both belong to same network
(b) (i)$\begin{array}{cc}225\cdot 225\cdot 225\cdot 128& \\ 255\cdot 255\cdot 255\cdot 10000000& \\ 10\cdot 105\cdot 1\cdot 01110001& IPofA\\ \overline{10\cdot 105\cdot 1\cdot 00000000}& \end{array}$

(ii) $\begin{array}{cc}255\cdot 255\cdot 255\cdot 10000000& \\ 10\cdot 105\cdot 1\cdot 01011011& IPofB\\ \overline{10\cdot 105\cdot 1\cdot 00000000}& \end{array}$

So both belong to same N/W
(d) (i) $\begin{array}{cc}255\cdot 255\cdot 255\cdot 11100000& \\ 10\cdot 105\cdot 1\cdot 01110001& IPofA\\ \overline{10\cdot 105\cdot 1\cdot 01100000}& \end{array}$

(ii)$\begin{array}{cc}255\cdot 255\cdot 255\cdot 11100000& \\ 10\cdot 105\cdot 1\cdot 010111011& IPofB\\ \overline{10\cdot 105\cdot 1\cdot 01100000}& \end{array}$
Both are not same so it not belong to same network.