5. IP/Datagram Forwarding (20 pt.) (show all the details/work for all questions-

Question

5. IP/Datagram Forwarding (20 pt.) (show all the details/work for all questions-a.b.c) a. Consider an IP subnet with prefix 129.17.129.97/27. Provide the range of IP addresses (of form xxx.xxx.xxx.xxx to yyy.yyy.yyy.yyy) that can be assigned to this subnet. (2 pt) (show all the details/work) b. Suppose an organization owns the block of addresses of the form 129.17.129.97/27. Suppose it wants to create four IP subnets from this block, with each block having the same number of IP addresses. What are the prefixes (of fom xxx.xxx.xxx/y) for the four IP subnets? (8 pt) (show all the details/work - include assumptions made) C. Consider the network shown below. Each of the subnets A-D contains at most 30 hosts; subnet E connects routers R1 and R2. (10 pt) Subnet B: Subnet C: Subnet E: Subnet A: R2 R1 Subnet D: to public Internet via ISP Assign network addresses (of form a.b.c.yyy/x) to the five subnets shown above (that is, write the addresses you have assigned. Note: a, b, & c remain the same (as the left-most 3 octets), but you will work to replace yyy and x). (show all the details/work -include assumptions made)

Explanation / Answer

Answer:-

a) Given IP address 129.17.129.97/27 = 10000001.00010001.10000001.01100001

10000001. 00010001. 10000001. 01100000 to 10000001. 00010001. 10000001. 01111111

or consistently, 129.17.129.96 to 129.17.129.127

b) There are 32 addresses the variety; we give 8 addresses to each block;

Thus, 129.17.129.96 to 129.17.129.103,

129.17.129.104 to 129.17.129.111,

129.17.129.112 to 129.17.129.119, and

129.17.129.120 to 129.17.129.127.

This means 129.17.129.97 -129.17.129.126

so, a total of 126 - 97 +1 = 30 hosts.

c) Each subnet wants to address up to 30 hosts, using the rightmost 5 bits of the address. The five subnet addresses are thus x.y.z...000/27, x.y.z.001/27, x.y.z.010/27, x.y.z.011/27, and where we have shown the first binary digits of the last byte of the addresses openly. More properly, these addresses are x.y.z.0/27, x.y.z.32/27, x.y.z.64/27, x.y.z,96/27, and x.y.z.128/27 in dotted decimal notation. Other answers with different bit values in bits 25, 26 and 27 are also possible, as long as the five three-bit patterns used are single.

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