SubnettingΒΆ

  • What you need to remember
/24 = 256
/25 = 128
/26 = 64
/27 = 32
/28 = 16
/29 = 8
/30 = 4
/31 = 2
/32 = 1
  • Location
A = /8 - /15
12345678.XXXXXXXX.12345678.12345678

B = /16 - /23
12345678.12345678.XXXXXXX.12345678

C = /24 - /32
12345678.12345678.12345678.XXXXXXXX

When it's located in A or B, shift it to C
ex = /18 shift to /26 (just shift it by 8)
     /9  shift to /17 (Still located in B), shift to /25
  • IP
10.10.10.50/30
20.20.20.50/28
30.30.30.30/19
40.40.40.40/13
  • Question
1. How many IP in subnet ?
2. Subnet Mask ?
3. IP Network, Broadcast, and Range IP Host ?
  • Answer for 10.10.10.50/30
/30 = 4
/30 located in C
1. How many IP in subnet ? 4
2. Subnet Mask ? 256 - 4 = 255.255.255.252
3. IP Network & Broadcast
/30 = 4

    Because its 4 then :
    0 - 3
    4 - 7
      .
      .
    48 - 51 ----> .50 located between 48 - 51

IP Network = 10.10.10.48
IP Broadcast = 10.10.10.51
IP Host = 10.10.10.48 - 10.10.10.50- Answer for 10.10.10.50/30
  • Answer for 20.20.20.50/28
/28 = 16
/28 located in C
1. How many IP in subnet ? 16
2. Subnet Mask ? 256 - 16 = 255.255.255.240
3. IP Network & Broadcast
/28 = 16

    Because its 16 then :
    0 - 15
    16 - 31
      .
      .
    48 - 63 ----> .50 located between 48 - 63

IP Network = 20.20.20.48
IP Broadcast = 20.20.20.63
IP Host = 20.20.20.49 - 20.20.20.62
  • Answer for 30.30.30.30/19
/19 = 32 (shifted /19 + 8 = /27)
/29 located in B
1. How many IP in subnet ? 32 x 256 = 8192
2. Subnet Mask ? 256 - 32 = 255.255.224.0
3. IP Network & Broadcast
/19 = 32

    Because its 32 then :
    0 - 31  ----> .30 located between 0 - 31

IP Network = 30.30.0.0
IP Broadcast = 30.30.31.255
IP Host = 30.30.0.1 - 30.30.31.254
  • Answer for 40.40.40.40/13
/13 = 8 (shifted /13 + 8 = /21 + 8 = /29)
/13 located in A
1. How many IP in subnet ? 8 x 256 x 256 = 524288
2. Subnet Mask ? 256 - 8 = 255.248.0.0
3. IP Network & Broadcast
/13 = 8

    Because its 8 then :
    0 - 7
    8 - 15
      .
      .
    40 - 47  ----> .40 located between 40 - 47

IP Network = 40.40.0.0
IP Broadcast = 40.47.255.255
IP Host = 40.40.0.1 - 40.47.255.254
Sources :
  • ID-Networkers