IP Addressing

In class C, 8 bits are reserved for Host Id and 24 bits are reserved for Network Id. Out of these 24 Network Id bits, the leading 3 bits are fixed as 110. So remaining 21 bits can be used for different networks. See this for more details.

In class C, 8 bits are reserved for Host Id and 24 bits are reserved for Network Id. Out of these 24 Network Id bits, the leading 3 bits are fixed as 110. So remaining 21 bits can be used for different networks. See this for more details.

See Question 4 of http://www.geeksforgeeks.org/computer-networks-set-1/

See question 2 http://www.geeksforgeeks.org/computer-networks-set-4-2/

See Question 3 of http://www.geeksforgeeks.org/computer-networks-set-7/

See question 1 of http://www.geeksforgeeks.org/computer-networks-set-10/

  Background required - Subnetting and SubNet Mask Answer - D Explanation - Suppose we have a host A with IP Address IP_A and Subnet mask of the subnet of which A is a part is M_s. Now when A wants to send packet to a host B with an IP address say IP_B, then A will first AND the subnet-Mask M_s with IP_A to find out the subnet-id ID_N of the subnet in order to identify whether IP_B belongs to the same network. Now if B also belongs to the same network, then IP_B BITWISE-AND M_s must be equal to ID_N which A has calculated. If IP_A and IP_B belongs to same network, we must have

	IPA BITWISE-AND Ms == IPBBITWISE-AND Ms

Out of the 4 options, only option D matches.

128.8.129.43 BITWISE-AND 255.255.31.0 = 128.8.1.0
128.8.161.55 BITWISE-AND 255.255.31.0 = 128.8.1.0

You can check rest of the options. This explanation has been provided by Pranjul Ahuja.

The next hop is decide according to the longest prefix matching.  Refer following link for details. https://www.youtube.com/watch?v=PSC5omE3pX8&list=PLkHsKoi6eZnzJl1qTzmvBwTxrSJW4D2Jj&index=32

10.0.0.1  and 172.16.0.10 are private IP address. Thus cannot be used in WAN.  15.1.5.6 is a public IP address.

192.168.1.255 is a Direct Broadcast Address (DBA),  DBA  can't be used as Source Address. 127.0.0.1 Loopback address again can't be used as the source address. 255.255.255.255 is Limited Broadcast Address, which cannot be used as DBA. 10.0.0.1 can be both used as both source and destination IP address.