• # what have i done wrong in this problem ?

I made up a problem with the following :-
Given network for 192.168.10.0/24 for VLSM :-
IT - 27 Hosts
Sales - 59 Hosts
HR - 20 Hosts
OF - 70 Hosts

Another network 192.168.11.0/24 for R-R connections:-
4 R-R networks

After VLSM i get the following :-

IT - 192.168.10.0/27
Range -> x.1-x.30
BC -> x.31

Sales - 192.168.10.32/26
Range -> x.33 - x.94
BC -> x.95

HR - 192.168.10.96/27
Range -> x.97 - x.126
BC -> x.127

OF - 192.168.10.128/25
Range -> x.129 - x.254
BC -> x.255

But when i go to a sub calculator to verify my VLSM, It shows that i have done the Sales wrong, So i checked by doing the AND operation and the 6th bit is not under the the Subnet mask which is the right cause of the issue.

Now did i come to the right conclusion ? and what is to be done in this case to fix the issue ?

• 6th bit in the 4th octet**

• I made up a problem with the following :-
Given network for 192.168.10.0/24 for VLSM :-
IT - 27 Hosts
Sales - 59 Hosts
HR - 20 Hosts
OF - 70 Hosts

But when i go to a sub calculator to verify my VLSM, It shows that i have done the Sales wrong, So i checked by doing the AND operation and the 6th bit is not under the the Subnet mask which is the right cause of the issue.

Now did i come to the right conclusion ? and what is to be done in this case to fix the issue ?

Here's the unusual things about the way subnetting calculators work. And also logically how we subnet as well. There is an "order" to doing it. That order is start with the largest subnet to smallest subnet.

This is the proper "order?" that works.

1st OF: - 192.168.10.0/25
Range -> x.0 - x.126
BC -> x.127

2nd Sales: -192.168.10.128/26
Range -> x.129 - x.190
BC -> x.191

3rd IT: -192.168.10.192/25
Range -> x.192 - x.222
BC -> x.223

4th HR: -192.168.10.224/25
Range -> x.225 - x.253
BC -> x.254

I do not know the technical term for this...its not an `order of operations` per se but an "value precedence(?)" in binary math that is programmed into the subnet calculators that is correct.

Here is the output of what happens if you do a smaller subnet proceeding a larger subnet:

``````Router(config)#int g0/0
Router(config-if)#no shutdown
Router(config-if)#
*Aug 27 11:25:26.947: %LINK-3-UPDOWN: Interface GigabitEthernet0/0, changed state to up
*Aug 27 11:25:27.948: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet
Router(config-if)#int g0/1
% 192.168.10.0 overlaps with GigabitEthernet0/0
% 192.168.10.0 overlaps with GigabitEthernet0/0
``````

Here is what happens when you do a smaller subnet after a larger subnet:

``````Router(config)#int g0/0
Router(config-if)#no shutdown
Router(config-if)#
*Aug 27 11:25:26.947: %LINK-3-UPDOWN: Interface GigabitEthernet0/0, changed state to up
*Aug 27 11:25:27.948: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet
Router(config-if)#int g0/1
% 192.168.10.0 overlaps with GigabitEthernet0/0
% 192.168.10.0 overlaps with GigabitEthernet0/0
Router(config-if)#no shutdown
Router(config-if)#
*Aug 27 11:28:20.027: %LINK-3-UPDOWN: Interface GigabitEthernet0/1, changed state to up
*Aug 27 11:28:21.027: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to up
Router(config-if)#
``````

Cordially,
Ronnie Wong
Edutainer, ITProTV

*if the post above has answered the question, please mark the topic as solved.
**All "answers" and responses are offered "as is" and my opinion. There is no implied support or guarantee by the ITProTV team.

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