VLSM subnetting question

[Jim79]

Hello, I hope you guys could help me out on a subnetting question I need to work through, Im really confused with VLSM and subnetting

 

How do I use VLSM to split 172.16.0.0/24 into 4 subnets? I need an IP address and subnet mask for router interfaces and sub interfaces (2 VLANs)

Appreciate any help on this, 

Thanks, 

Jim. 

 

[ddennis002]

17 minutes ago, Jim79 said:

Hello, I hope you guys could help me out on a subnetting question I need to work through, Im really confused with VLSM and subnetting

 

How do I use VLSM to split 172.16.0.0/24 into 4 subnets? I need an IP address and subnet mask for router interfaces and sub interfaces (2 VLANs)

Appreciate any help on this, 

Thanks, 

Jim. 

 

How many hosts do you need per subnet?

[ddennis002]

25 minutes ago, Jim79 said:

Hello, I hope you guys could help me out on a subnetting question I need to work through, Im really confused with VLSM and subnetting

 

How do I use VLSM to split 172.16.0.0/24 into 4 subnets? I need an IP address and subnet mask for router interfaces and sub interfaces (2 VLANs)

Appreciate any help on this, 

Thanks, 

Jim. 

 

So say you want to split your whole 172.16.0.0/24 evenly and you don't care how many host are on each Subnet it would look like this

                                                                                                               172.168.x.x

Subnet Name  # of Host    Address          Mask    Dec Mask                Assignable Range         Broadcast Address

           A                 62       172.16.0.0         /26      255.255.255.192      x.x.0.1 - x.x.0.62            172.16.0.63

           B                62        172.16.0.64      /26      255.255.255.192      x.x.0.65 - x.x.0.126         172.16.0.127

          C                 62        172.16.0.128    /26      255.255.255.192     x.x.0.129 - x.x.0.190        172.16.0.191

          D                 62        172.16.0.193    /26      255.255.255.192     x.x.0.193 - x.x.0.254         172.16.0.255

[Jim79]

Hi ddennis002 , thanks for replying. 

 

Its not specified how many host are required per subnet if that makes sense. 

 

Looking at your response, if I need to assign IP address to hosts on a router what address could I use, do I take then form the 

assignable range? 

 

Thanks 

Jim 

[Eniqmatic]

10 minutes ago, Jim79 said:

Hi ddennis002 , thanks for replying. 

 

Its not specified how many host are required per subnet if that makes sense. 

 

Looking at your response, if I need to assign IP address to hosts on a router what address could I use, do I take then form the 

assignable range? 

 

Thanks 

Jim 

Indeed, use one from the range, just do not use the broadcast address.

 

Great answer btw!

[ddennis002]

3 hours ago, Jim79 said:

if I need to assign IP address to hosts on a router what address could I use, do I take then form the 

assignable range? 

Correct! so you can use any address in the assignable rage for your Router, PCs, ect. Usually when I do multiple subnets I use a /16 subnet and leave space in between and leave gaps to increase the number of hosts over time when needed. This helps in a lot of ways such as

improve network performance and speed.

Reduces network congestion.

Helps with network security.

Control over network growth.

Easier administration.

[mynameisjuan]

@Jim79

 

To clear up how he got the 4 subnets.

 

So remember 2^n. Its everwhere in subnetting and very important from number of networks to number of host.  So lets take your example 172.16.0.0/24. That is 24 subnet bits and 8 host bits. Look at it this way before even looking at the network.

 

11111111.1111111.11111111.xxxxxxxx

 

They want you to split it into 4 networks, how many bits does it take to get 4? Remember the formula. 2^2 = 4. To split that address all you need to do is steal 2 host bits.

 

11111111.1111111.11111111.00xxxxxx

 

So now what you are left with is a /26. Out of those two bits you stole you can make 4 networks. 0000000, 01000000, 1000000, 11000000 which in decimal comes out to 0, 64, 128, 192

 

Now just slap on what ever network you like or were given and boom. 172.16.0.0, 172.16.0.64, 172.16.0.128, 172.16.0.192.

 

I hope it clears it up a tad. Subnetting is much simipler than it appears. Just remember that you are just taking a subnet and breaking it down. Always look at it at a high level, dont get caught up with the actual network until the very end. Just take the subnet say a /21 and say "okay to break it into 8 networks, 2^n=8...3 bits need to be stolen from host so now I have 8 /24s. Then you can just take you original network and add the subnet mask for each.

[Jim79]

Folks, really appreciate all of your reply's, its really helped me out. 

 

I may have a some follow up Q's but for now - thank you!