Sub interface Ip address over-laping

[mayandamkhwanazi07]

I'm doing a small school project for a small business with 5 departments and each department has 10 employees which makes a total of 50 employees. I used a 192.168.1.0 network address and a /27 as a subnet mask to subnet my network into 5 department which ended up giving me 8 subnets, 32 hosts and 30 usable addresses for each subnet. I had only one problem of assigning Ip address to the sub-interface of a router, I kept getting this error. Please help me solve this problem ! 

Router(config-sub if)#ip address 192.168.1.1 255.255.255.0

Router(config-sub if)#exit

Router(config)#interface gigabit Ethernet 0/0/0.20

Router(config-sub if)#encapsulation dot1Q 20

Router(config-sub if)#ip address 192.168.1.33 255.255.255.0

% 192.168.1.0 overlaps with GigabitEthernet0/0/0.10

Router(config-sub if)#exit

please help !

[Flavio Miranda]

Hi

 You are using the wrong mask

192.168.1.1 255.255.255.0

Should be

192.168.1.1 255.255.255.224

[TotallyTodd]

Hi, the proper subnet mask for a /27 would be 255.255.255.224 to allow for 8 subnets totally. The reason that this overlaps is because the 255.255.255.0 creates 1 subnet with a total of 254 host addresses totally. The rest looks good! 

[Joseph W. Doherty]

"Hi, the proper subnet mask for a /27 would be 255.255.255.224 to allow for 6 subnets totally."

Actually, a /24 provides 8 /27s (as OP correctly noted.)

Otherwise, as both @Flavio Miranda and @TotallyTodd note, you're using a /24 mask, when you need to use a /27 mask.