Hi @wisamani,
If you don’t supply a wildcard then EIGRP will assume you want the whole network to be advertised. Here’s an example:
Router(config)#router eigrp 1
Router(config-router)#no auto-summary
Router(config-router)#network 1.1.1.0
This is what is stored in the running config:
Router#show run | begin router eigrp
router eigrp 1
network 1.0.0.0
1.1.1.0 falls under the class A 1.0.0.0/8 range so that’s what EIGRP adds to the running config. If you don’t want this, you have to add a wildcard:
Router(config)#router eigrp 1
Router(config-router)#no network 1.0.0.0
Router(config-router)#network 1.1.1.0 0.0.0.255
And you will get:
Router#show run | begin router eigrp
router eigrp 1
network 1.1.1.0 0.0.0.255
Even without the wildcard, it would have worked but enabling EIGRP for all 1.x.x.x networks might not be what you want.
I didn’t have to do this for 192.168.12.0 since that’s a class C network. If I used a /25 - /30 subnet mask then I would have to add the correct subnet mask.
Hope this helps!