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VLAN & VLSM Help

I currently work at a school who have a /22 network assigned to them by the state school department. All the schools in the state are connected to each other through a WAN. The network address they got assigned is 10.135.164.0. My boss would like to implement a few VLANS but the problem is they want the 1st VLAN to be a specific IP range.


So far this is what I've planned:


The 1st VLAN is meant to support 100 hosts so i gave it a /25 subnet.

The 2nd VLAN will be the teachers and students VLAN and I gave them a /23 subnet

The 3rd VLAN is for VOIP, which I gave a /26 subnet


These 3 subnets fit easily in


There is also a Admin subnet which is small and uses a completely different subnet which doesnt need to be touched at all.


Now I know from studying CCNA you are meant to use biggest to smallest for VLANS, but the school system REQUIRES the servers, management IP's for switches, printers etc to use the 10.x.x.1 - 10.x.x.100 range.


So my question is, am I able to use the VLANS in this specific order:


VLAN 1: 126 hosts /25

VLAN 2: 510 hosts /23

VLAN 3: 62 hosts /26


What would the VLAN 2 and VLAN 3 subnet come out to be, can I just continue to VLSM as normal after the 1st subnet?

Subnet Name

Size

Address

Mask

Dec Mask

Assignable Range

Broadcast

VLAN 1

126

10.135.164.0

/25

255.255.255.128

10.135.164.1 - 10.135.164.126

10.135.164.127

VLAN 2

510

10.135.164.128

/23

255.255.254.0

10.135.164.129 - 10.135.

VLAN 3

62

/26

255.255.255.192

3 Replies 3

Mahesh Gohil
Level 7
Level 7

Hi,

you have /22 subnet

10.135.164.0/22

If you divide it in two subnet it will be

10.135.164.0/23
10.135.166.0/23

if you further divide in /24 it will be

10.135.164.0/24
10.135.165.0/24

10.135.166.0/24
10.135.167.0/24

vlan1: 10.135.164.0/25 already used so remaining is 10.135.164.128/25


vlan2: you can not use 10.135.164.128/23 it is not valid
       better you use next /23 subnet which is 10.135.166.0/23

vlan3: you have now 10.135.164.128/25 or 10.135.165.0/24 to be used
         if you want of /26

Hope this helps

Regards

Mahesh

Hi Mahesh, thanks for taking the time to look at a solution

For the 3rd VLAN, would it be possible to further subnet down a 10.135.164.128/25 to get:

10.135.164.128/26

10.135.164.129 - 10.135.164.190 range

I just don't want to be using a /24 or /25 for only about 30-50 VOIP phones

So my scheme would look like this:

Subnet Name

Size

Address

Mask

Dec Mask

Assignable Range

Broadcast

VLAN 1

126

10.135.164.0

/25

255.255.255.128

10.135.164.1 - 10.135.164.126

10.135.164.127

VLAN 2

510

10.135.166.0

/23

255.255.254.0

10.135.166.1 - 10.135.167.254

10.135.167.255

VLAN 3

62

10.135.164.128

/26

255.255.255.192

10.135.164.129 - 10.135.164.190
10.135.164.191

Yes you can use a /26, there is no problem with that.

Jon