06-20-2008 06:56 AM - edited 03-05-2019 11:44 PM
I'm trying to break up a /24 subnet for one of my sites in order to create VLANs.
I want to break up 192.168.100.0/24 like this:
192.168.100.1/26 (for 62 hosts)
192.168.100.65/25 (for 126 hosts)
I know there are portions of the subnet left over but I don't need them currently. When trying to configure the router (Cisco 2651XM) for subinterfaces I get the error:
Router(config)#int f0/0.10
Router(config-subif)#encap dot1q 10
Router(config-subif)#ip address 192.168.100.1 255.255.255.192
Router(config)#int f0/0.11
Router(config-subif)#encap dot1q 11
Router(config-subif)#ip address 192.168.100.65 255.255.255.128
% 192.168.100.0 overlaps with FastEthernet0/0.10
If I'm using VLSM then the /26 subnet I placed on f0/0.10 would range from 192.168.100.0-63 and would leave the 192.168.100.65 address available to put in a different subnet. What am I missing?
06-20-2008 07:00 AM
You can't subnet it the way you have. Change it to
192.168.100.0/25
192.168.100.128/26
192.168.100.0/25 will give you
192.168.100.1 -> 192.168.100.126 with .127 as the broadcast address.
192.168.100.128/26 will give you
192.168.100.129 -> 192.168.100.190 with .191 as the broadcast address.
Edit - have at a look at this thread for why your original subnetting wouldn't work.
Jon
06-20-2008 07:47 AM
Sorry, having a bit of a moment :-)
Here's the link to the thread.
Jon
06-20-2008 07:53 AM
Quinton:
Your statement:
"If I'm using VLSM then the /26 subnet I placed on f0/0.10 would range from 192.168.100.0-63 and would leave the 192.168.100.65 address available to put in a different subnet. What am I missing?"
... demonstrates that you have carefully considered 192.168.100.1/26, but then you transition to assumption.
You need to consider 192.168.100.65/25, and the address space that represents.
You have focussed on "65", whereas your focus should be on the "/25" mask.
As Jon suggested, its best that you reconsider it, and arrive at the understanding yourself.
06-23-2008 12:26 AM
Hi,
As your subnet /25 overlaps the subnet /26.So better will be if u use
192.168.100.0-63 for f0/0.10
&
192.168.100.128-255 for f0/0.11
pls let me know the status.
regards,
Raj
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