#vlsm

[ithdo]

VLSM ( Variable Length Subnet Mask)

[routerswitchlab-blog]

Route - IP addressing (part 2)

Subnetting

NOTE:This decimal converted binary value will be use through out this post. 128  64  32  16  8  4  2  1

Before we go to subnetting process. Let us review the IP address and network mask. Let us site an example.

Given 192.168.200.0 /24 ip address block. Let's try to interpret how network device will read this.

Take a look on Network Mask (binary value). Just remember that all

Also, remember that each address should have network address, usable host range and broadcast address. For the network device (such as router) to properly locate the specific host or target.

Let us get started.

Looking at the example above. How do we identify the network,host and broadcast address?

To compute for Network ID (or network address) - we use Logical AND (or we should I say multiply) IP address (binary value) to Network Mask (binary value)

To compute for Broadcast address - Bring down the network address + convert binary host portion to 1

To define the Usable address - the number start after NETWORK ID and it ends before BROADCAST ID. The number of usable address can be computed also by 2n - 2; where "n" = number of host bits.

I hope above information encourage you to know subnetting :). Now let us tackle subnetting.

Subnetting

is the process to create small group of network to maximize the use of IP address block buy borrowing a binary bit/s (called subnet ID) from the host portion (in binary value).

“On this post I will try to explain the proper procedure and the shortcut that I know. It is on your decision which procedure is more convenient for you.”

Subnetting - Proper Method

Procedure:

1. Determine the classful network mask if the prefix is not define. 2. Determine how many subnet bits needed for the required number of networks. Use this formula  2 raise to subnetid = number of required networks. And look for the new network mask (called subnet mask) 3. Determine the Delta (sometimes called Increment); where Delta = to the decimal value of the right most binary 1. 4. Plot the network, usable and broadcast address and its subnet mask

Example1:

Given: 192.168.35.0 How many networks do I need for above diagram? The Answer is 4. (Remember in CCNA each router interface is 1 broadcast domain) What are the IP address I can assign to each router interface and to hosts?

Let us use the procedure above.

1. Determine the classful network mask if the prefix is not define. Answer is 255.255.255.0 (since the given address is part of Class C)

2.Determine how many subnet bits needed for the required number of networks. Use this formula  2 raise to subnetid = number of required networks. And look for the new network mask (called subnet mask)

Needed networks = 4

We are after really about subnet bits.

Therefore;

3. Determine the Delta (sometimes called Increment); where Delta = to the decimal value of the right most binary 1.

The right most  binary 1 is located on the Octet 4. Using 128  64  32  16  8  4  2  1  value, Delta = 64

Subnet mask = 255.255.255.192 (/26)

4. Plot the network, usable and broadcast address using value of Delta and its subnet mask

4.a. plot the Network address;  Delta = 64

4.b. plot the Broadcast address. The last address before the next Network address is  a broadcast address.

4.c. plot the Usable address. These are the adress range between Network Address and Broadcast Address.

Please NOTE that we are not assigning Network and broadcast address to any devices.

Let us assign the IP address to each network device interfaces.

Subnetting - Shortcut method 

( Aha! so may shortcut pala! ) Actually you just need to memorize the procedure, formula and by practice.

Procedure (Looking for numberof network address)

1. Using our hand to compute the subnet bits. Using this Formula 2 4 8 16 32 64 128 256 512 1024 and so on...

2. Look Delta and subnet mask

3. Plot the network address

Example:

Given 192.168.20.0  : Required 16 network.

1. Using our hand to compute the subnet bits. Using this Formula 2 4 8 16 32 64 128 256 512 1024 and so on...

The formula I'm using is counting this on using my starting from  2  4  8  16  32 64 128 256 512 1024 and so on... since I need 16 network, using the formula above how many finger I used.

Above information - means that we need 4 subnet bits to create 16 network.

2. Look Delta and subnet mask

Delta = 16

Subnet Mask = 255.255.255.240 (/28)

Remember that Delta is the right most binary bit 1 (in decimal form) of a new netmask which is 16

For Subnet Mask - 128+64+32+16 = 240

3. Plot the network address

The increment of each subnet is 16 as we seen above. I only look for the NETID (network address) because from there we can identify the usable address and broadcast address.

Network Address for network1            = 192.168.20.0 /28 Usable address for network1           = 192.168.20.(1 - 14) /28 Broadcast address of network1       = 192.168.20.15 /28

Another example: Given: 172.16.0.0 /16 : Required network is 32 Formula: 2 4 8 16 32 64 128 256 512 1024 Answer: Subnet bits = 5

Procedure (Looking for number of host address)

1. Counting again by hand and using this formula again 2 4 8 16 32 64 128 256 512 1024..so on (minus 2 )

2. Plot the host portion

3. Look Delta and subnet mask

4. Plot the network address

Example: 192.168.0.0 ; required 16 hosts per subnet.

1. Counting again by hand and using this formula again 2 4 8 16 32 64 128 256 512 1024..so on (minus 2 )

Using this formula again 2 4 8 16 32 64 128 256 512 1024..so on (minus 2 ) Here, we should focus on the host portion. Means how many host bits (0) do we need to cater 16 hosts per subnet?

This example is tricky! Is it correct that we only need 4 host bits? Answer is NO. Remember, IP address block should have network and broadcast address. That is the reason why we need to subtract 2. because 16 -2  = 14 host only. We need to add another host bit.

And the correct answer should be below.

Host bits = 5 which is 32 -2 = 30 hosts per subnet.

2. Plot the host portion

OK! Now I know the host bits. How will i know the subnet mask ,   and NET ID for each subnet.

Check the given again. 192.168.0.0 is part of class C. Means that the default nework mask is /24 (or 255.255.255.0) Meaning we cannot modify the first 3 octet. Because subnetting is borrowing subnet bits from the host portion. In Class C network. the host portion is Octet4. Procedure here is to plot the "0s" from right to left. The rest make "1s".

3. Look Delta and subnet mask

From above table, we can now determine the other subnetting requirements.

4. Plot the network address

Another example: (This time try to use your mind to get the answer) Given: 10.16.0.0 /8; Required 100 users per subnet.

VLSM (Variable Length Subnet Mask)

This subnetting technique is commonly used by networks today to maximize the use of IP  address block by creating different subnet size. If you will notice, subnetting can divide classful network. But they still found out some waste of usable address. For example we have a IP block with a prefix of /25 - meaning 126 address are the usable address and for point-to-pint connection only 2 address are needed and the rest will be unused. And most of the time engineers are focus on usable address for each block when doing this.

Giving an example:

NOTE:

For VLSM - always create the subnet the largest first to smallest network requirement. The rest are the same with subnetting procedure. Let us start by defining the required network from largetst to smallest.

So we finish the VLSM table. Let us know assign these addresses to our network design above.

In practical world, VLSM is commonly use but you need to give allowance on your computation for your company future expansion. That is the reason, why large company uses class A (10.X.X.X) for their internal network communication.

Try to follow my example until you become familiar with the computation.

Supernetting / CIDR / Route summarization

I would say Supernetting is most commonly use by engineers for route summarization. It is a summarization of a multiple subnets under a common network prefix - also known as CIDR (Classles Inter Domain Routing). Procedure: 1. Plot the network address  in binary value. 2. On all of the network address, look for the significant bit which is common to all network address bits. Count the number of common bits 3. Find the summarize network address prefix and subnetmask

Example: On the diagram below, R1 wants to see a summarize network for each company. In order to provide the requirement. R2 and R3 needs to advertise their summarize network towards R1.

1. Plot the network address  in binary value.

2. On all of the network address, look for the significant bits which is common to all network address bits. Count the number of common bits

3. Find the summarize network address prefix and subnet mask.

Using the value we got above, we can now use it for R2 and R3 to advertise their summarize attached networks towards R1

In R1 routing table, it should be like this 192.168.0.0 / 19 via R2 directly connected address 172.16.0.0 /17 via R3 directly connected address

Please hit like and follow my blog if this helps you.

[lenorajohnson-blog1]

Online VLSM CIDR Subnet Calculator https://www.vlsmcalculator.online Allocate your ip addresses easily using Online VLSM CIDR Subnet Calculator.

[deredes]

CCNA2 - Clase 4: VLSM (Variable Length Subnet Mask) y CIDR (Classless Interdomain Routing)

Estos videos corresponden a los cursos de instructor CCNA dictados por la Academia de Networking de Cisco perteneciente a la Universidad Tecnológica de Chile INACAP.

[deredes]

CCNA1 - Clase 6: Creación de Subredes con Máscaras de Longitud Variable (VLSM)

Estos videos corresponden a los cursos de instructor CCNA dictados por la Academia de Networking de Cisco perteneciente a la Universidad Tecnológica de Chile INACAP.

[reseausale]

vlsm tutorial

vlsm tutorial and Explained The following procedure shows how VLSM can be used in order to allocate department-wise IP addresses as mentioned in the example.

Step - 1

Make a list of Subnets possible.

Step - 2

Sort the requirements of IPs in descending order (Highest to Lowest).

Sales 100

Purchase 50

Accounts 25

Management 5

Step - 3

Allocate the highest range of IPs to the highest requirement, so let's assign 192.168.1.0 /25 (255.255.255.128) to Sales department. This IP subnet with Network number 192.168.1.0 has 126 valid Host IP addresses which satisfy the requirement of Sales Department. The subnet Mask used for this subnet has 10000000 as the last octet.

Step - 4

Allocate the next highest range, so let's assign 192.168.1.128 /26 (255.255.255.192) to Purchase department. This IP subnet with Network number 192.168.1.128 has 62 valid Host IP Addresses which can be easily assigned to all Purchase department's PCs. The subnet mask used has 11000000 in the last octet.

Step - 5

Allocate the next highest range, i.e. Accounts. The requirement of 25 IPs can be fulfilled with 192.168.1.192 /27 (255.255.255.224) IP subnet, which contains 30 valid host IPs. The network number of Accounts department will be 192.168.1.192. The last octet of subnet mask is 11100000.

Step - 6

Allocate next highest range to Management. The Management department contains only 5 computers. The subnet 192.168.1.224 /29 with Mask 255.255.255.248 has exactly 6 valid host IP addresses. So this can be assigned to Management. The last octet of subnet mask will contain 11111000. By using VLSM, the administrator can subnet the IP subnet such a way that least number of IP addresses are wasted. Even after assigning IPs to every department, the administrator, in this example, still left with plenty of IP addresses which was not possible if he has used CIDR. vlsm Tags: vlsm,VLSM Explained,vlsm tutorial

vlsm tutorial from le monde informatique http://ift.tt/1h4p5RJ

[allankarter]

Protocolos de Roteamento

Boa noite.

 Hoje vamos conhecer um pouco de alguns protocolos de roteamento.

*Imagem meramente ilustrativa.

ClassLess e ClassFull.

Protocolos RIPv1 e IGRP não propagam sua máscara de rede durante sua atualização de rotas, por este motivo eles são considerados CLASSFULL.

Como consequência não suporta: Sub-rede, VLSM, Sumarização.

Com essas dificuldades, teve a necessidade de adotar um protocolo CLASSLESS, o RIPv2 e EIGRP.

 Propaga máscara e suportando: Sub-rede, VLSM, Sumarização

Próxima matéria será sobre o Protocolo RIPv1 e RIPv2.

Até a próxima!

[ark-teleco]

IP subnetting. Direccionamiento VLSM.