Class B Subnetting
Subnetting Requirement
Host Requirement
2^h ≥ required Hosts “h” Number of Required Zero To get required Hosts
Network Requirement
2^n ≥ Required Network “n” Number of Required One To get required Subnets
172.16.0.0/16 Host requirement is---->1000hosts
2 ^h ≥1000
2^10≥1000 1024 ≥ 1000
I need 10 bits zero in the new subnet mask
Default mask is 255.255.0.0
New mask is 255.255.11111100.00000000 /22 Or 255.255.252.0
Block size ————–> last bit one value 2^2=4
1.172.16.0.0 /22 number of valid host per subnet 2^10-2
2.172.16.4.0 /22 Number Of available subnets 2^6
3.172.16.8.0 /22 1024*64=65536 (full range)
4.172.16.12.0 /22
5.172.16.16.0/22
6.172.16.20.0/22
7.172.16.24.0/22
8.172.16.28.0/22
9.172.16.32.0/22
172.16.0.0/16 Host requirement is---->2000hosts
2 ^h ≥2000
2^11≥2000 2048 ≥ 2000
I need 11 bits zero in the new subnet mask
Default mask is 255.255.0.0
New mask is 255.255.11111000.00000000 /21 Or 255.255.248.0
Block size ————–> last bit one value 2^3 = 8
1.172.16.0.0 /21 number of valid host per subnet 2^11-2
2.172.16.8.0 /21 Number Of available subnets 2^5
3.172.16.16.0 /21 2048*32=65536 (Full Range)
4.172.16.24.0 /21
5.172.16.32.0/21
6.172.16.40.0/21
7.172.16.48.0/21
8.172.16.56.0/21
9.172.16.64.0/21
172.16.0.0/16 Host requirement is---->4000hosts
2 ^h ≥4000
2^12≥1000 4096 ≥ 4000
I need 12 bits zero in the new subnet mask
Default mask is 255.255.0.0
New mask is 255.255.11110000.00000000 /20 Or 255.255.240.0
Block size ————–> last bit one value 2^4=16
1.172.16.0.0 /20 number of valid host per subnet 2^12-2
2.172.16.16.0 /20 Number Of available subnets 2^4
3.172.16.32.0 /20 4096*16=65536 (full range)
4.172.16.48.0 /20
5.172.16.64.0/20
6.172.16.80.0/20
7.172.16.96.0/20
8.172.16.112.0/20
9.172.16.128.0/20
172.16.0.0/16 Host requirement is---->8000hosts
2 ^13 ≥8000
2^13≥8000 8192 ≥ 8000
I need 13 bits zero in the new subnet mask
Default mask is 255.255.0.0
New mask is 255.255.11100000.00000000 /19 Or 255.255.224.0
Block size ————–> last bit one value 2^5 = 32
1.172.16.0.0 /19 number of valid host per subnet 2^13-2
2.172.16.32.0 /19 Number Of available subnets 2^3
3.172.16.64.0 /19 8192*8=65536 (Full Range)
4.172.16.96.0 /19
5.172.16.128.0/19
6.172.16.160.0/19
7.172.16.192.0/19
8.172.16.224.0/19
172.16.0.0/16 requirement is---->4 Subnets
2 ^n ≥4
2^2≥4 4 ≥ 4
I need 2 bits one in the new subnet mask
Default mask is 255.255.0.0
New mask is 255.255.11000000.00000000 /18 Or 255.255.192.0
Block size ————–> last bit one value 2^6=64
1.172.16.0.0 /18 number of valid host per subnet 2^14-2
2.172.16.64.0 /18 number Of available subnets 2^2
3.172.16.128.0 /18 16,384*4=65536 (full range)
4.172.16.192.0 /18
172.16.0.0/16 requirement is---->2 subnets
2 ^n ≥2
2^1≥2 2 ≥ 2
I need 1 bits one in the new subnet mask
Default mask is 255.255.0.0
New mask is 255.255.10000000.00000000 /17 Or 255.255.128.0
Block size ————–> last bit one value 2^7 = 128
1.172.16.0.0 /17 number of valid host per subnet 2^15-2
2.172.16.128.0 /17 number Of available subnets 2^1
32,768*2=65536 (Full Range)