CCNA-Notes/15. Subnetting (Part 3 - VLSM).md

id, aliases, tags

id	aliases	tags
1777971486-WJIG	Subnetting (Part 3)

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 ?

10101100.00010101.01101111.11001001 172.21.111.201 10101100.00010101.01100000.00000000 172.21.96.0

Quiz question 3

What is the broadcast address of the network 192.168.91.78/26

11000000.10101000.10110011.01001110 192.168.91.78 11000000.10101000.10110011.01111111 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 10101100.00011010.00000000.00000000 broadcast: 172.16.0.0/18 10101100.00011010.00111111.00000000 172.16.63.255/18

Subnet 2 : Network address 172.16.64.0/18 10101100.00011010.01000000.00000000 broadcast: 172.16.65.0/18 10101100.00011010.01111111.00000000 172.16.127.255/18

Subnet 3 : Network address 172.16.128.0/18 10101100.00011010.10000000.00000000 broadcast: 172.16.128.0/18 10101100.00011010.10111111.00000000 172.16.191.255/18

Subnet 4 : Network address 172.16.192.0/18 10101100.00011010.11000000.00000000 broadcast: 172.16.192.0 10101100.00011010.11111111.00000000 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 00001010.00000000.00000000.0000000

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
4. Last usable address:10.223.255.254
5. Nuber of host (usable) address: 2,097,150

10.217.182.223 00001010.11011001.10110110.11011111

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