Why do these ip addresses overlap

[razvan102]

I'm trying to do a lab in PT. and get the following error:

Router(config)#int fa0/0
Router(config-if)#ip add 172.16.136.129 255.255.255.128
Router(config-if)#exit
Router(config)#int fa1/0
Router(config-if)#ip add 172.16.137.1 255.255.224.0
% 172.16.136.0 overlaps with FastEthernet0/0

The last address for 172.16.136.128/25 is 172.16.136.255, which is not an address of 172.16.137.0/19

[Todd Burrell]

fa0/0 would be in this network: 172.16.136.128 /25 so the address range would be 172.16.136.128-172.16.136.255
fa1/0 would be in this network: 172.16.128.0 /19 so the address range would be 172.16.128.0 through 172.16.159.255

Thus these 2 addresses are in subnets that overlap. And I apologize up front for any math errors - I did this quickly.

I would recommend making the subnet mask for FA1/0 255.255.255.0

[martell1000]

fa0/0 would be in this network: 172.16.136.128 /25 so the address range would be 172.16.136.128-172.16.136.255
fa1/0 would be in this network: 172.16.128.0 /19 so the address range would be 172.16.128.0 through 172.16.159.255

Thus these 2 addresses are in subnets that overlap. And I apologize up front for any math errors - I did this quickly.

I would recommend making the subnet mask for FA1/0 255.255.255.0

172.16.136.128 /25 is still part of 172.16.136.0 /24 you will need to divide the 172.16.136.0 /24 subnet into two /25 subnets