VLAN subnetting

justice41

Hello everyone. I've got a bit of problem with the network setup I am making. Quite new to networking, so please excuse me.

I have 10.10.11.0 /24 network but would like to separate it to different subnets.

Namely
VLAN1 - 10.10.11.0 / 28
VLAN2 - 10.10.11.17 / 27
VLAN3 - 10.10.11.50 / 25

However enabling the interfaces throws IP overlap error. What might the mistake here... Thanks!

johnpoz

@justice41 said in VLAN subnetting:

10.10.11.17 / 27

.17/27 would be host address in the network 10.10.11.0-31

and .50/25 host address in .0-127

.17 and .50 are not subnet boundaries

Did you mean
.0/28 = 10.10.11.0 - 10.10.11.15, first host being .1
.16/29 = 10.10.11.16 - 10.10.11.23, first host being .17
.24/29 = 10.10.11.24 - 10.10.11.31, first host being .25

Or maybe
.0/28 = 10.10.11.0 - 10.10.11.15
.16/28 = 10.10.11.16 - 10.10.11.31
.32/28 = 10.10.11.32 - 10.10.11.47

Your vlans there do overlap - /27 and /25 are larger subnets than your /28

Other than a learning exercise, for such subnets.. why would you just not use /24. Was 10.10.11 given to you, and you need to subnet into different vlans all within the .11/24?

Say would be much easier.
10.10.11.0/24
10.10.12.0/24
10.10.13.0/24

You have all of rfc1918 to work with.. why would you use anything other than /24 since they fall on different boundaries that can be difficult to spot unless your very familiar with where they are.. while /24 all break at the 3rd octet 10.10.X, and its very easy for the human eye to spot..

While I am all for using appropriate sized vlans.. Unless you have some constraint you have to work with other than all of rfc1918 space.. /24 is the easiest to use, and most common.

If you wanted to break up your .11 there to those sized subnets
.0/25 would = first half 10.10.11.0 - 10.10.11.127

then you could take the other /25, .128/25 = 10.10.11.128 - 10.10.11.255

And break it up into smaller chunks

.128/26 = 10.10.11.128 - 10.10.11.191
.192/26 = 10.10.11.192 - 10.10.11.255

or say
.128/26 = 10.10.11.128 - 10.10.11.191
.192/27 = 10.10.11.192 - 10.10.11.223

Which would leave you another /27
.224/27 = 10.10.11.224 - 10.10.11.255

Not exactly sure where you want to break up your .11.0/24, how many hosts do you need/want in each vlan?

justice41

Thanks for the reply.

The plan is to chunk 10.10.11.0 / 24 into appropriate sizes and separate to put routing behind. While its easy to just make another /24 network, considering only few hosts would take one network, seems its better just to make subnets.

While at it. It seems that smaller to bigger chunks does not work indeed. Though big to small chunks seemed to work.

So /25 then /27, and /28. Although instead of /27,/28. Would be more ok to do two /26 as you said, so not to waste any space. Since that would be much easier to adjust for future changes.

Anyways. Its ok now. Thank you.

johnpoz

@justice41 said in VLAN subnetting:

considering only few hosts would take one network, seems its better just to make subnets.

True.. I applaud your wanting to use appropriate sized networks. Then again rfc1918 is HUGE.. For any single location.. So what does it matter ;)

Unless for some reason your limited to this 10.10.11/24 for some reason.

You can chunk up your /24 anyway you like in whatever sizes you want.. You could break them up into /30s if you so desire.. But you need to chunk them up so that your subnets don't overlap ;)