--- id: 1777971486-WJIG aliases: - Subnetting (Part 3) tags: [] --- # Subnetting (Part 3 - VLSM) class B Refference table | Prefix | Subnets | Hosts | | ------ | ------- | ----- | | /17 | 2 | 32766 | | /18 | 4 | 16382 | | /19 | 8 | 8190 | | /20 | 16 | 4094 | | /21 | 32 | 2046 | | /22 | 64 | 1022 | | /23 | 128 | 510 | | /24 | 256 | 254 | --- class C Refference table | Prefix | Subnets | Hosts | | ------ | ------- | ----- | | /25 | 2 | 126 | | /26 | 4 | 62 | | /27 | 8 | 30 | | /28 | 16 | 14 | | /29 | 32 | 6 | | /30 | 64 | 2 | | /31 | | (0) | | /32 | | (0)-2 | ## QUIZ Question 1 You have been given the 172.30.0.0/16. your company requires 100 subnets with at least 500 hosts per subnet. What prefix length should you use? I should use 172.168.0.0/23 because it compatible with 100 subnet and 500 hosts subnet mask -> 255.255.254.0 ## Quiz Question 2 What subnet does host 172.21.111.201/20 belong to ? 10101100.00010101.*0110*1111.11001001 172.21.111.201 10101100.00010101.*0110*0000.00000000 172.21.96.0 ## Quiz question 3 What is the broadcast address of the network 192.168.91.78/26 11000000.10101000.10110011.*01*001110 192.168.91.78 11000000.10101000.10110011.*01*111111 192.168.91.127 ## Quiz question 4 You divide the 172.16.0.0/16 network into 4 subnets of equal size. Identify the network and broadcast addresses of the second subnet Subnet 1 : Network address 172.16.0.0/18 10101100.00011010.*00*000000.00000000 broadcast: 172.16.0.0/18 10101100.00011010.*00*111111.00000000 172.16.63.255/18 Subnet 2 : Network address 172.16.64.0/18 10101100.00011010.*01*000000.00000000 broadcast: 172.16.65.0/18 10101100.00011010.*01*111111.00000000 172.16.127.255/18 Subnet 3 : Network address 172.16.128.0/18 10101100.00011010.*10*000000.00000000 broadcast: 172.16.128.0/18 10101100.00011010.*10*111111.00000000 172.16.191.255/18 Subnet 4 : Network address 172.16.192.0/18 10101100.00011010.*11*000000.00000000 broadcast: 172.16.192.0 10101100.00011010.*11*111111.00000000 172.16.255.255/18 ## Quiz question 5 You divide the 172.30.0.0/16 network into subnets of 1000 hosts each. How many subnets are you able to make I'm able to make 64 subnets ## Subentting class A Networks The process of subnetting Class A, Class B and Class C networks is Exactly the same ! ### Example 2 You hace been given the 10.0.0.0/8 network. You must create 2000 subnets which will be distributed to various enterprises. What prefix length must you use ? How many host addresses usable addresses will be in each subnet? 10.0.0.0 00001010.00000000.0000000.0000000 2, 4, 8, 16,32, 64,128,256, 512, 1024, 2048 00001010.*00000000.000*00000.0000000 Answer: 10.0.0.0/19 8192 - 2 = 8190 hosts ### Example 2 PC1 has an IP address of 10.217.182.223/11. Identify the following for PC1's subnet: 1) Network address:10.192.0.0/11 2) Broadcast address: 10.223.255.255 3) First usable address: 10.192.0.1 3) Last usable address:10.223.255.254 3) Nuber of host (usable) address: 2,097,150 10.217.182.223 00001010.*110*11001.10110110.11011111 ## [[VLSM]] Variable-Length Subnet Masks - Until now, we have practiced subentting used FLSM (Fixed-Length Subnet Masks). - This means that all of the subents use the same prefix length (ie. subnetting a class C into 4 subenets using /26). - VLSM (Variable-Length Subnet Masks) is the process of creating subnets of different sizes to make your use of network addresses more eficient - VLSM is more complicated than FLSM, but it's easy if you folow the steps correctly. ### Exaple 1 We must divide 192.168.1.0/24 must divided between 5 subnets Tokyo Lan A = 110 Hosts --- Tokyo Lan B = 8 Hosts | Router | Router | Toronto Lan A = 29 Hosts --- Toronto Lan B = 45 Hosts #### VLSM Steps 1) Assign the largest subnet at the start of the address space. 2) Assign the second- largest subnet after it. 3) Repeat the process until all subnets have been assigned we will do this in this order Tokyo LAN A -> Toronto LAN B -> Toronto LAN A -> Tokyo LAN B -> Point to point ##### Tokyo LAN A Network address: 192.168.1.0/25 Broadcast address: 192.168.1.127/25 First usable address: 192.168.1.1/25 Last usable address: 192.168.1.126/25 Total Number of usable host address: 126 ##### Toronto LAN B if we add 1 to the Tokyo Broadcast address we get the next Network address Network address: 192.168.1.128/26 Broadcast address: 192.168.1.191/26 First usable address: 192.168.1.129/26 Last usable address: 192.168.1.190/26 Total Number of usable host address: 62 ##### Toronto LAN B Network address: 192.168.1.192/27 Broadcast address: 192.168.1.223/27 First usable address:192.168.1.193/27 Last usable address:192.168.1.222/27 Total Number of usable host address:30 ##### Tokyo LAN A Network address: 192.168.1.224/28 Broadcast address: 192.168.1.239/28 First usable address: 192.168.1.225 Last usable address: 192.168.1.239 Total Number of usable host address: 14 ##### Point to Point Network address: 192.168.1.240/30 Broadcast address: 192.168.1.243/30 First usable address: 192.168.1.241/30 Last usable address: 192.168.1.242/3 Total Number of usable host address: 2 ## Additional Practice - https://www.subnettingquestions.com - https://www.subnetting.org - https://www.subnettingpractice.com