Hello Takele
Let’s say you have a router R1 with the following configuration:
FastEthernet 0/1 has an IP address of 192.168.10.1/24
FastEthernet 0/2 has an IP address of 10.10.10.1/24
FastEthernet 0/3 has an IP address of 172.16.2.1/24
Here’s the topology:
Now let’s say that we’ve included all three subnets in the EIGRP process using the network command. This means that all updates R1 sends will contain all three subnets. Now by default, EIGRP will sent out hello and update packets out of all of its interfaces. But as you can see in the diagram, there’s no point i sending these updates out of Fe0/2 and Fe0/3 because there are no routers attached to these subnets. So, we can make these two interfaces passive.
Now this doesn’t exclude the networks on these interfaces from participating in EIGRP, but it just says that these physical interfaces will not send out EIGRP hello and update packets. From this you can easily see that R2 will still get an update that contains all three networks. So even networks on passive interfaces are advertised, just not via those interfaces themselves.
I hope this has been helpful!
Laz