IP Addressing

IP Summarization

Which two subnetworks would be included in the summarized address of 172.31.80.0 /20

A)     172.31.17.4 /30

B)      172.31.51.16 /30

C)      172.31.64.0 /18

D)     172.31.80.0 /22

E)      172.31.92.0 /22

F)      172.31.192.0 /18

Solution:

Step 1# 172.31.80.0 /20

Step 2# Convert to binary

      172       .          31      .        80         .       0

1010 1100 . 0001 1111 . 0101 0000 . 0000 0000

Step 3#

 1010 1100 . 0001 1111 . 0101 0000 . 0000 0000

----------------------------  32 bits  -----------------------

32 bits – 20 = 12

2⁴ = 16                                    172.31. 80 – 0 - 0000

                                                                81 – 1 - 0001

                                                                82 – 2 - 0010 

                                                                83 – 3 - 0011

                                                                84 – 4 - 0100

                                                                85 – 5 - 0101 

                           86 – 6 - 0110

                                                                87 – 7 - 0111

                                                                88 – 8 - 1000 

                89 – 9 - 1001

                                                                90 – 10 - 1010

                                                                91 – 11 - 1011 

               172.31. 92 – 12 - 1100

                                                                93 – 13 - 1101

                                                                94 – 14 – 1110

                                                                95 – 15 – 1111

ANSWER: 172.31.80.0 /22

    172.31.92.0 /22