Question

Consider a datagram network using 32-bit host addresses. Suppose a router has four links, numbered through 3, and packets are to be forwarded to the link interfaces as follows. Destination Address Range Link Interface 0 11101111010000000000000000000000 through 11101111111111111111111111111111 1 11101111010110000000000000000000 through 11101111010010011111111111111111 11101001 111110000000000000000000 through 11101001 111111111111111111111111 2 otherwise 3 a) Provide a forwarding table that has 4 entries, uses longest prefix matching, and forwards packets to the correct link interfaces. (4 pts) b) Describe how your forwarding table determines the appropriate link interface for datagrams with destination addresses: (3 pts) 111011110100011100001111 00000000 111011110100111100001111 00000000 11111000 11001000 11111111 00000000 HTRE

Answer 1

a)

Prefix Match	Link Interface
11101111	0
11101111 010	1
11101111 11111	2
otherwise	3

b) To find the correct interface we need to find the longest match that a destination address can make.

i) The starting part is 11101111 010 which matched the prefix for interface 1.

ii) The starting part is 11101111 010 which matches the prefix for interface 1 again.

iii) The starting part is 1111 which does not matches any prefix so it will be forwarded to interface 3.

Hope this helps. If you have any queries or suggestions regarding the answers please leave them in the comments section so I can update and improve the answer. Thank you.