IPv4 Supernetting

[zekebashi]

Hello,

I'm trying to expand one of our subnets and wanted to get some input to check and see if I'm doing the calculation properly:

The requirement is to create a /19 subnet (172.18.64.0/19) to use for wireless network; however,  I'd like to use a /23 for the wired network out of this subnet 172.18.64.0/19).  Meaning that I want to be able to carve out a /23 out of the /19 range. Would this be possible?

172.18.64.0/19

172.18.64.0

172.18.64.1 - 172.18.95.254

172.18.95.255

Thanks in advance,

~zK

[balaji.bandi]

yes you can do as below.

172.18.64.0/23 ( 255.255.254.0)

172.18.64.0 - 172.18.65.255

Sorry i misunderstood the question here.. @Georg Pauwen is right. you can not have, but you can split the /19 in to small subnet as example i mentioned.

[Georg Pauwen · Accepted solution]

Hello,

the short answer is: no, you cannot use a smaller subnet, since you would have overlapping address spaces. The router won't even let you configure this...

Router(config-if)#ip address 172.18.64.1 255.255.224.0
*Nov 2 22:38:57.908: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to up
Router(config-if)#ip address 172.18.64.1 255.255.224.0
Router(config-if)#exit
Router(config)#int gigabitEthernet 0/1
Router(config-if)#ip address 172.18.66.1 255.255.254.0
% 172.18.66.0 overlaps with GigabitEthernet0/0

[paul driver · Accepted solution]

Hello

Yes you can but as stated you would need to cidr it off into two /20 then only use a /23 from one of those /20 

Example:

         172.18.64.0 /19
172.18.64.0/20   172.18.64.80/20

          172.18.64.0/20
172.18.64.0/21 172.18.72.0/21

         172.18.64.0/21

172.18.64.0/22 172.18.68.0/22

      172.18.64.0/22

172.18.64.0/23 172.18.66.0/23

172.18.64.0/23 

172.18.64.1 -172.18.65.254