(CISCO Packet Tracer) Overlap Error

Question

I am trying to set up a network of for different organisational departments based on a given typology:

Using Cisco 2911 routers & 2960-24TT Switches.

With given addressing of:

'EIGRP 101' 172.16.16.0 /16
and
'OSPF 2018' Addressing of 192.168.17.0 /24

from this I created a network addressing scheme:

Using my addressing scheme and based on the given typology - I have attempted to recreate in Packet Tracer the network here:

As you can see in the top left 'Management' department subnet I have managed to set up Router0 through the Gi0/2 interface using the router's CLI. However, using my addressing scheme, I was unable to set up the same router for the 'Engineering' department through Router0's Gi0/1 interface due to a 'overlap' error:

Press RETURN to get started!

Router>en Router#conf terminal  Enter configuration commands, one per
line.  End with CNTL/Z. 
Router(config)#interface gigabitEthernet 0/2 
Router(config-if)#ip address 172.16.16.1 255.255.0.0
Router(config-if)#no shutdown 

Router(config-if)#
%LINK-5-CHANGED: Interface GigabitEthernet0/2, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/2, changed 
state to up

Router(config-if)#do wr
Building configuration...
[OK]
Router(config-if)#exit
Router(config)#interface gigabitEthernet 0/1
Router(config-if)#ip address 172.16.16.65 255.255.0.0
% 172.16.0.0 overlaps with GigabitEthernet0/2
Router(config-if)#

Is my addressing scheme wrong? Or am I using the Packet Tracer or the routers CLI incorrectly?

Thanks!

Answer 1

That is because your networks are part of the same network. Look at your network mask. If you mask the 172.16.x.x addresses with the 255.255.0.0 mask you have assigned, you will see that all those networks are the same network. The same thing applies to the 192.168.17.x network and its 255.255.255.0 mask.

Routers route packets between networks, not from a network back to the same network, so each router interface must be in a different network, but you are assigning the same network to multiple router interfaces, and that will generate an error.

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You need to understand IPv4 network math. See this answer for an explanation of IPv4 address manipulation and subnetting.

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Also, EIGRP and OSPF will not share routes unless you redistribute routes between them, and you would need a router that runs both protocols to do that. Routing protocols do not route, they exchange route information between routers.

Answer 2

its because the two department are on the same network of 0.0 255.255.0.0. Put the two interface router linking management and engineering on different network and do a route.